Infectious diseases/immunology Flashcards
NEWS score 6 components, low risk, urgent ward based response x2, emergency response cut offs) - 4 step process when contacted about a pt
resp rate, sats (including whether theyre on room air, O2 etc), (systolic) blood pressure, consciousness assessed with AVPU or any new onset confusion, and body temp
aggregate score 0-4 is low, needs simple ward based response
red score of 3 is scoring 3 only, but all within one category eg blood pressure; needs urgent ward based response including ABCDE
aggregate of 5/6 also needs urgent ward based response, and in both of these urgent responses must be aware that you may need to escalate to a critical care team/ rap response team
agg 7+ needs an emergency response potentially including staff with critical care skills, including airway management
for all pt requests your process should be -> is this pt covered by my dept? what is their NEWS (ie how critically unwell are they)? are they in shock/sepsis? (by checking the obs); then evaluate
also note all of this applies to new NEWS score - if high level but stable you may not need to do anything
GRASP abx prescribing
check Guidelines, check Renal function and weight, check Allergies, check Sensitivity of organism if available, check Previous abx (if one tried before and not working prob not worth trying again)
antibiotic classes and mechanisms (10 word mnemonic; class that inhibs folate synthesis; class that inhibits DNA replication/synthesis; 4 that inhibit protein synthesis inc acronym; 4 classes that inhibit cell wall synthesis; what is temocillin inc class, good against what, used for treatment of what, not active against what; fusidic acid mechanism)
Antibiotics Can Terminate Protein Synthesis For Microbial Cells Like Germs
Antibiotics = Aminoglycosides = 30s inhib protein synthesis
Can = Cephalosporins = Inhib cell wall synthesis (b lactam)
Terminate = Tetracyclines = 30s inhib protein synthesis
Protein = Penicillins = Inhib cell wall synthesis (b lactam)
Synthesis = Sulfonamides = Inhibit folate synthesis
For = Fluoroquinolones = Inhibit DNA replication - inhibiting bacterial DNA topoisomerase and DNA-gyrase
Microbial = Macrolides = 50s inhib protein synthesis
Cells = Carbapenems = Inhibit cell wall synthesis (b lactam)
Like = Lincosamides = 50s inhib protein synthesis
Germs = Glycopeptides = Inhib cell wall synthesis
Inhibit Folate Synthesis
Sulfonamides are the main class to inhibit folate synthesis.
This can be remembered because both sulFOnamide and FOlate contain “FO”.
Inhibit DNA Replication
Fluoroquinolones are the main class to inhibit DNA replication/synthesis.
Think of quintuplets as having identical copies of DNA (DNA replication).
Use the “QUIN” in fluoroQUINolones and QUINtuplets to help you remember DNA replication inhibition.
Inhibit Protein Synthesis
Macrolides, aminoglycosides, lincosamides, and tetracyclines all inhibit protein synthesis.
Use the acronym “MALT” and think of malt powder that is sometimes found in “protein” shakes.
This will help you remember Macrolides, Aminoglycosides, Lincosamides, and Tetracyclines (MALT) inhibit protein synthesis.
Inhibition Cell Wall Synthesis
Lastly, through process of elimination the final 4 antibiotic classes inhibit cell wall synthesis: cephalosporins, penicillins, carbapenems, and glycopeptides.
note: temocillin is older penicillin type with unusual stability against ESBL β-lactamases used primarily for the treatment of multiple drug-resistant, Gram-negative bacteria, though it has efficacy against various species (not active against g+ve)
fusidic acid - acts as a bacterial protein synthesis inhibitor by preventing the turnover of elongation factor G (EF-G) from the ribosome. Fusidic acid is effective primarily on Gram-positive bacteria and is bacteriostatic
gentamicin - who not to use in x3, standard proph and rx dose (+max single dose and how to round), what kind of weight to use in obese ppl and why, levels (when to take after 1st dose, 3 groups where you need to know pre-dose before giving 2nd dose, how often to check after this (x2), what if pre-dose level raised x4, 2 reasons to discuss with micro, if using for IE standard treatment regime including when to check pre and post dose initially and what they should be then how often to check; 7 toxic outcomes)
Gentamicin should not be used in the
following patient groups:
* Myasthenia Gravis
* Hypersensitvity to aminoglycosides
* Pregnancy
- The standard prophylaxis dose is 3mg/kg
- The standard treatment dose is 5mg/kg OD,
- No single dose of Gentamicin should exceed 520mg
- Doses should be rounded down to the nearest 40mg
- Online gentamicin dose calculator can be used instead of standard dosing if you can work out CrCl
Doesn’t distribute well in fat so use ideal body weight in obese ppl
Take pre dose levels up to one hour before the second dose is given
* Patients >65 years old, or with abnormal renal function or poor urine output: the pre dose gentamicin level must be ≤1mg/litre before any further dose is given; otherwise you can give second dose before result from first is back; if eGFR <60 then you need to wait for pre-dose level
* For patients with normal and stable renal function check pre dose level twice weekly
* For patients with abnormal renal function, check the pre dose gentamicin level before each dose
if pre-dose level >1mg/L then withhold next dose and consider reasons why it might have become high; rpt at 12-24hrs, you can’t give next dose until <1mg/L; you may need to increase dosing interval from 24 hours - seek advice on adjusting from micro; you should check renal function and that sample wasn’t taken from same line used to give gent
discuss with micro if longer than 7 days needed or if eGFR <30
if using gent for IE: 1mg/kg TDS take pre and post (1 hr after) levels before 3rd or 4th dose; pre should be <1mg/kg and post 3-5mg/kg; check levels twice weekly, if outside range seek advice
toxic outcomes: nephrotoxic, hypersensitivity (urticaria, eosinophilia, delayed-type hypersensitivity reaction (Stevens-Johnson syndrome and toxic epidermal necrolysis), angioedema, and anaphylactic shock), ototoxicity on longer courses
vancomycin - who not to use in x3, dosing (normal, adjusting based on age x2), when to initially check levels x2 then how often to check x2; pre-dose target range x3, what to do if pre-dose level is low or high, and 2x to discuss with micro; how to increase doses and when to discuss with micro based on this) toxic outcomes x6
should not be used in the following patients:
* Hypersensitivity to Glycopeptides
* Major Burns (>20% of body surface area)
* Pregnancy
Normal dose 1000mg every 12 hours (750mg if 65-75yo, 500 if >75)
if eGFR <45 then measure level at 24hr and wait for results before giving next dose; otherwise first level check before 3rd or 4th dose and can give next dose before result back; then assay pre-dose every 72 hours unless unstable renal function in which case check before every dose
pre-dose levels 10-15 for serious/deep infections, otherwise 5-15; for some IE and other infections 15-20 may be allowed; if pre-dose levels low then increase dose; if higher than 15 then omit dose and either reduce dose or increase interval, re-checking as per first check above; if very high or renal function worsening then hold until within range and d/c with micro
if increasing doses go to 1.25g in first instance, then 1.5g - if more needed than this then discuss with micro
vancomycin is nephrotoxic, causing AIN or ATN; + characteristic redman syndrome, ototoxicity, DRESS and anaphylaxsis
bacti classes (2:5:2:5) and g+ve vs g-ve structure
g+ cocci - strep, staph
g+ bacilli - Actinomyces Bacillus Clostridia, (corynebacterium) diphtheria, listeria
g- cocci - Neisseria, moraxella
g- bacilli - Most other bacteria! E. coli, Klebsiella, Salmonella, Shigella, Haemophilus
also non staining ones
Gram-positive bacteria
Have a thick layer of peptidoglycan in their cell wall, and lack an outer membrane. This thick layer retains crystal violet stain during the Gram stain test, causing gram-positive bacteria to appear purple under a microscope.
Gram-negative bacteria
Have a thin layer of peptidoglycan in their cell wall, surrounded by an outer membrane containing lipopolysaccharides. During the Gram stain test, the alcohol used to decolorize the sample degrades the outer membrane of gram-negative bacteria, making it more porous and unable to retain the crystal violet stain
bacti types - G+ cocci sorting based on catalase, coag, and haemolysis tests; G+B mnemonic 5 bugs; GP anaerobes x4; atypical pneumonia mnemonic x5; common G- x7
G+ cocci: catalase pos is staph, coag pos is staph aureus, coag neg is spidermidis or saprophyticus;
cat neg is strep, beta haem (clear) is GAS (pyogenes) or GBS (agalactiae), gamma haem (none) is enterococ, alpha haem (green) is pneumoniae or viridans
G+ bacillus: corney Mike’s list of basic cars”:
Corney – Corneybacteria
Mike’s – Mycobacteria (but not really)
List of – Listeria
Basic – Bacillus
Cars – Nocardia
GP anaerobes: Use the mnemonic “CLAP”:
C – Clostridium
L – Lactobacillus
A – Actinomyces
P – Propionibacterium
atypical bacteria that cause atypical pneumonia can be remembered using the mnemonic “legions of psittaci MCQs”:
Legions – Legionella pneumophila (g-)
Psittaci – Chlamydia psittaci
M – Mycoplasma pneumoniae (g-)
C – Chlamydydophila pneumoniae
Qs – Q fever (coxiella burneti) (g-)
Common gram negative organisms are:
Neisseria meningitis
Neisseria gonorrhoea
Haemophilus influenza
E. coli
Klebsiella
Pseudomonas aeruginosa
Moraxella catarrhalis
notifiable diseases - what notably isn’t, 6 things that are
NOT HIV
Most likely to be relevant to SAQ: TB, meningitis, encephalitis, malaria, infectious diarrhoea, food poisoning
managing tetanus risk with injuries - 3 routes (1:2:2 including definition of wound risk criteria 3:5:3)
Patient has had a full course of tetanus vaccines, with the last dose < 10 years ago
no vaccine nor tetanus immunoglobulin is required, regardless of the wound severity
Patient has had a full course of tetanus vaccines, with the last dose > 10 years ago
if tetanus prone wound: reinforcing dose of vaccine
high-risk wounds (e.g. compound fractures, delayed surgical intervention, significant degree of devitalised tissue): reinforcing dose of vaccine + tetanus immunoglobulin
If vaccination history is incomplete or unknown
reinforcing dose of vaccine, regardless of the wound severity
for tetanus prone and high-risk wounds: reinforcing dose of vaccine + tetanus immunoglobulin
Clean wounds are less than 6 hours old, non-penetrating and have negligible tissue damage
Tetanus-prone wounds include compound fractures, certain animal bites and scratches, puncture-type injuries acquired in a contaminated environment, wounds or burns with systemic sepsis, and wounds containing foreign bodies—this list is not exhaustive.
High-risk tetanus-prone wounds include any tetanus-prone wounds or burns that either show extensive devitalised tissue or require surgical intervention that is delayed more than 6 hours, or wounds that are heavily contaminated with material likely to contain tetanus spores (such as soil or manure).
sepsis definitions - SIRS definition, newer definition (and how key component defined plus screening for high risk -> what counts as raised and what to do if raised), why was definition changed
old definition based on meeting SIRS criteria + a source of infection; but since 2016 consensus definition has been life-threatening organ dysfunction caused by a dysregulated host response to infection, with organ dysfunction defined as acute increase in total SOFA score, and qSOFA as a way to identify those with infection who are likely to dev sepsis - qSOFA is positive if 2/3 of altered mental state (GCS <15), sysBP <100, RR >22 (and if qSOFA increases by 2 or more then suspect sepsis/organ dysfunction)
an increase of two or more in the qSOFA score should create a suspicion of sepsis, and organ dysfunction assessment should be conducted; if qSOFA >2 (or less but still think it might be sepsis) then do full SOFA, and if that is greater than or equal to 2 then it is sepsis, if not then monitor and re-evaluate
definition changed as many states may show SIRS like appearance and would be managed quite differently to sepsis; by old definition, almost all infection accompanied by symptoms of systemic inflammatory reaction will be diagnosed as sepsis, most of which, in fact, can be easily cured; SIRS has low sensitivity and specificity in discriminating sepsis and non-complicated infection
sepsis resus (6 steps - 3:1(3 choices):3:2:3:3)
large bore cannula, 2x blood cultures, and start abx
then 30 ml/kg IV fluid - start with plasmalyte/hartmanns, can do 20% albumin - possible but debatable mortality benefits but at least get haemodynamic stability faster, blood only to get Hb >70
arterial line and central line, titrate MAP - start norad if ScvO2, urine output, lactate clearance etc still not good enough
dobutamine or adr can be added as inotrope if still not improving
if still refractory despite adequate preload and contractility support and norad not working alone then add vasopressin, hydrocortisone, and consider possibility of toxic shock (add IVIg and clindamycin)
if still not then bicarb if pH <7.15, can consider ionised Ca, angiotensin II - at this point less well-evidenced but worth a try
sepsis mx kids - assess (2 scoring systems), 11 things in first 15 mins (inc 13-15 bloods), 7 in 15-30 (inc 9 ix), 3 things after this inc fluids max (2 limits) and lactate target + inotrope options (inc when to start earlier, how to give, 4 things to exclude if no response, 2ndry options if 1st choice not working 2:3, another alt, and discuss with who; how fast to start inotropes if fluids not working), 8 after this, final resort (2 indications)
assess with traffic light system and PEWS score
in first 15 mins: give O2, have continuous sats + ECG monitoring and BP cuff set to 3 minute cycle, get senior r/v, get bloods (culture, gas, CRP, FBC, U&Es, LFTs, bone profile, Mg, glucose, coags (+ D-Dimer/FDPs), G&S, ASOT, viral and bacti blood PCR)
give 10ml/kg bolus of Hartmanns or plasmalyte (Push by hand, can use normal saline if that’s what you have), re-assess and give 2nd if needed (fluid resistant if not responding to 40ml/kg); broad spectrum abx (ceftriaxone; if <1mo then cefotaxime + amox; if indwelling line/VP shunt add vanc; if TSS signs add clinda), treat any hypoglyc with 5mls/kg 10% dex (+add hydrocortisone), start aciclovir if suspect possible HSV or <1mo, add dexamethasone if meningitis and old enough
15-30mins: ventilate as needed - note avoid propofol due to haemodynamic effects (but use ketamine), ITU/anaesthetic help (priority call), 2nd IV access; if after 1st fluid bolus still hypotensive, prolonged CRT, raised lactate then give second bolus; prepare inotropes, alert transfer service; get urine dip, send viral PCR (serum plus NPA swab), throat swab for rapid GAS test, COVID and flu swabs, sputum culture, CXR, consider LP based on nice guidelines and presence of contras
30-60mins: catheter, can repeat fluid boluses up to 60ml/kg if no hepatomeg, crackles, iWOB, or gallop rhythm - aim is to see lactate falling by >10% every hour - pts can require 100-200ml/kg in total but beware overload; start peripheral dose norad (warm shock) or adr (cold shock) (start earlier if above fluid overload/heart failure signs seen), can add 2nd inotrope + hydrocort (if 2nd inotrope or hypoglyc seen); both start at 0.1mcg/kg/min and titrate up to 1mcg/kg/min max) ;if you have IO or central access then give central doses of inotropes - IO and PVC admin need frequent monitoring for extravasation; if no response then exclude tamponade, PTX, ongoing blood loss or intracranial pathology and give hydrocort; 2nd options discuss with transport but for cold could do norad or milrinone, for warm could do adr followed by vasopressin or milrinone; dopamine is an option instead of adr/norad; ideally start inotropes within 15mins if fluids not working
60mins: arterial line or central line, aim for Ca >1.1, Hb >70, transfuse plats if <20, give vit K if PT prolonged, if fibrinogen low suggests DIC so give cryoprecipitate 5-10ml/kg
bicarb generally only if pH <7.15 or known renal failure, correct hypomag
if completely refractory or devs RDS then may need ECMO
long-term sepsis mx kids (how long does fluid shift/hypotension continue and 4 things to titrate fluids against; 3 options if pt is fluid overloaded’ 7 complications; warm vs cold shock inc normal order, commoner in which age ranges)
Fluid shift & hypotension secondary to capillary leak can continue for several days.
Continued fluid administration should be titrated against clinical end points such as serum lactate, urine output, heart rate, MAP
diuretics, peritoneal dialysis or continuous veno veno haemofiltration (CVVH) can be used for those patients who are fluid overloaded & unable to maintain fluid balance
complications:
ARDS
Acute/chronic renal injury
DIC
Mesenteric ischemia
Acute liver failure
Myocardial dysfunction
Multiple organ failure
warm in an earlier, more compensated state where BP maintained, will have warm extremities, bounding pulses, CRT <1s; cold as begin to become decompensated and BP falls with cold extremities, prolonged CRP and weak pulses; most adolescents/adults have warm shock only (unless cardiogenic etc), babies and young kids tend more towards cold shock due to worse ability to compensate by changing CO
toxic shock syndrome (what pt also often has; 2 commonest toxins, consider in which 2 groups, how do superantigens work; what else causes damage; how many criteria needed for definite diagnosis (+4 major crit and 3 minor + what test might show it); strep TSS phase features 8 (inc 2 dd for if in limb):3:1; blood cultures more likely in which kind of TSS?; abx choice for both inc mechanism of second agent + another med to give
pt will often have, or progress to, sepsis
TSS is caused by exotoxin producing cocci. TTS Toxin type-1 (TSST-1) and Staphylococcal enterotoxin B are the most commonly implicated toxins responsible for TSS; consider in any unwell pt with staph (abscesses, burns, surgery etc) or group A strep; superantigens seem to bind MHC class II outside of antigen groove and TCR to bypass antigen limited cell activation giving massive immune response - the large number of activated T-cells secrete large amounts of cytokines, the most important of which is Interferon gamma. This excess amount of IFN-gamma in turn activates the macrophages. The activated macrophages, in turn, over-produce proinflammatory cytokines such as IL-1, IL-6 and TNF-alpha; other toxins (eg DNase and tissue destroying enzymes) and virulence factors can also cause damage
confirmed staph TSS case is defined by the presence of all major criteria and three or more minor criteria, along with exclusionary evidence of other disease processes. Major criteria are fever ≥38.8 °C, a diffuse, macular erythrodermic rash, skin desquamation 1–2 weeks after onset of illness (particularly palms and soles), and hypotension. Minor criteria include the involvement of three or more organ systems (eg weakness with raised CK, confusion, liver dysfunction, vomiting etc); other sources of bacti/viral infection will be negative, blood cultures may also be negative - can consider MRSA pcr screen which might show it
strep TSS usually 3 phases; first phase which precedes the onset of severe hypotension by 24–48 h. is a severe influenza-like illness characterized by high fever, myalgia, headaches, and chills. Nonspecific digestive symptoms such as nausea, vomiting, and diarrhea. delirium is reported in roughly half of patients. Skin lesions as possible streptococcal infection may be present inc cuts, bulla, erythema, transient macular rash may be present, predominating on the upper chest, or desquamation on palms/soles; infected area (limb, abdo, thorax etc) often much more painful than clinically would suggest - this discrepancy should raise suspicion; painful limb would raise suspicion of nec fasc -> look for gas bubbles, nec fasc also tends to feel tense/woody vs softer strep infection; also consider compartment syndrome (pressure monitoring, myoglobin in urine)
systemic manifestations, such as tachycardia, tachypnea, and high fever make up the second phase; third phase is progression to shock
blood cultures more likely to be positive in iGAS TSS than in staph TSS
IV abx - vanc ets for staph, PenG (benpen)for strep; + clinda which inhibits protein synthesis by blocking the 50S sub-unit of the bacterial ribosome to reduce production of the destructive toxins and superantigens; also consider IVIg for staph and strep TSS to neutralise the toxins and opsonise bacti
PIMS-TS - what it is and 2x things it shares featues with, 3 things to trigger you to think of it, 8 features, discuss with who, 10mx
a significant inflam response to COVID19, sharing features with kawasakis and TSS; COVID testing may be pos or neg
fever >38.5deg lasting 3+ days w abnormal FBC or CRP levels and no clear cause should trigger you to consider PIMS
criteria is fever 38.5+ for 3+ days + 2 of hypotension, rash/conjunctivitis, coagulopathy, GI sx, myocardial dysfunction (echo trop or proBNP) + raised inflam markers/WCC + no other cause inc TSS or sepsis
discuss with rheum and immunology/ID
cover with cef +/- clinda, get ECHO within 24hrs, abdo USS and surgical r/v if abdo sx, give IV methylpred 10mg/kg and IVIg 2g/kg; give asprin 3-5mg/kg and if d-dimer >5x upper limit of normal then anticoagulate; rheum advice on switch IV to oral steroid and wean, and f/up in PIMS-TS clinic; follow up ECHO monitoring will be needed too; will need daily ECG while inpatient
line sepsis
cultures ideally pre abx
Paired line and peripheral blood cultures taken and clearly labelled, including separate and labelled culture from each lumen of a multilumen port
review for other source of infection as line infection may be secondary
check previous cultures and early senior review including whether to try and salvage line (not recommended generally)
usually remove line and send tip for culture
Line salvage therapy should only be considered when it is thought to be in the best interests of the patient and the benefits associated with this are thought to outweigh the risks. For example, in patients with multiple previous lines, limited ongoing options for vascular access, or a significant bleeding risk; need to weigh up against risk of ongoing or recurrent infection or sepsis
if attempting to salvage you need to do abx lock, guided by cultures and ideally a different class to the one infused systemically; taurolock, vanc, gent, cipro and others used - make up to specific volume, place in line, leave and don’t flush, and then aspirate it from line prior to using it for anything else; don’t leave it sitting for more than 24 hours, consult guidelines or specialists for specific choice and length of time to leave in; systemic abx should be given through the suspect line with locks in between; if line to be removed give abx through alternate access
post line removal discuss with micro/PID re: length of abx therapy to continue - often 7-14 days
septic shower occurs when bugs released from a place theyre growing into the system, can be from eg endocarditis but also line infection, can get unwell quite quickly including septic shock, and then either dies or recovers
MRSA and PVL screening and decolonisation
high risk groups:
ITU/CCU/NICU
Paeds HDU and ITU
Paeds cardiology/cardiothoracics
Anyone with history of MRSA
Any pt with (or planned to have) a PICC or midline
intermediate risk:
paeds onc
low risk:
all other paeds pt
all high risk need MRSA screening within 6 hours of admission and topical suppression with daily chlorhexidine wash + nasal mupirocin
intermediate need only daily wash
low need nothing
alternative to mupirocin is naseptin but contains peanut ingredients so caution in allergy
neonatal sepsis 8 risk factors and how these inform mx - 3 options and 4ix/1mx (2 choices of combo)
Vaginal GBS colonisation
GBS sepsis in a previous baby
Maternal sepsis, chorioamnionitis or fever > 38ºC
Prematurity (less than 37 weeks)
Early (premature) rupture of membrane
Prolonged rupture of membranes (PROM)
red flag risk factor: multiple babies one of which has sepsis
assess for red and amber flag features of neonatal sepsis (also note kaiser pathway system another way of scoring risk and deciding if to start abx)
If there is one risk factor or amber clinical feature, monitor the observations and clinical condition for at least 12 hours
If there are two or more risk factors or amber clinical feature of neonatal sepsis (or one red flag) start antibiotics
Antibiotics should be started if there is a single red flag
Antibiotics should be given within 1 hour of making the decision to start them
Blood cultures should be taken before antibiotics are given
Check a baseline FBC and CRP
Perform a lumbar puncture if infection is strongly suspected or there are features of meningitis (e.g. seizures)
benzylpenicillin and gentamicin; if after 72 hours flux and gent
fever in a child - inc how to measure in <4 weeks old; 7 things to get in history; scoring systems to use x2 (how one informs decision to admit, inc 4 reasons to admit), what if fever >5 days, 13 red flag features. antipyretic x2 and crit to start/stop, dehydration 4 signs and 2mx, school advice)
<4wks electronic thermometer in axilla; older can use that or infrared tympanic
other symptoms, perinatal and obstetric history (if an infant), immunization history, foreign travel, contact with anyone who has an illness; any family experiences with fevers (inc ICE)
PEWS + NICE traffic light system: red features call ambulance/admit; amber features consider admission (<3mo with suspected uti, unwell for a while but no obvious cause, significant parental anxiety), otherwise safety net
if fever for >5 days beware possibility of kawasaki disease
red flag features: pale/ashen/mottled/cyanotic, no response to social cues, cant stay awake, weak high pitched or continuous cry, appears very ill, grunting, RR >60bpm, moderate + chest indrawing, reduced skin turgor, fever >38deg and pt <3mo old, status epilepticus, FNS, signs of meningitis
management - paracetamol or ibuprofen to reduce distress from fever, stop once calmed and dont use aspirin; dehydrated and hypovol maybe dont use ibuprofen; dont give both at same time; if monotherapy is ineffective then alternate; keep watch for poor urine output, sunken fontanelle, dry mouth, absent tears; regular fluid intake, higher if dehydrated; continue breast feeding; check regularly inc at night; keep off nursery/school until better
traffic light system what to do for each colour
If green:
Child can be managed at home with appropriate care advice, including when to seek further help
If amber:
provide parents with a safety net or refer to a paediatric specialist for further assessment
a safety net includes verbal or written information on warning symptoms and how further healthcare can be accessed, a follow-up appointment, liaison with other healthcare professionals, e.g. out-of-hours providers, for further follow-up
If red:
refer child urgently to a paediatric specialist
7 ix to do if <3mo w fever, LP 3 times to do if <3mo, 3 times to give abx if <3mo (what to give); if >3mo with red features on traffic light then 8ix, what to do in children >3mo with fever but no apparent source and how to re-assess children with amber/red features
Full blood count
Blood culture
C-reactive protein
Urine testing for urinary tract infection
Chest radiograph only if respiratory signs are present
Stool culture, if diarrhoea is present
Resp swab
also do LP if:
infants younger than 1 month
all infants aged 1–3 months who appear unwell
infants aged 1–3 months with a white blood cell count (WBC) less than 5 × 109/litre or greater than 15 × 109/litre
and give parenteral abx to
infants younger than 1 month with fever
all infants aged 1–3 months with fever who appear unwell
infants aged 1–3 months with WBC less than 5 × 109/litre or greater than 15 × 109/litre
should give cefotaxime + amoxicillin
if >3mo w red features on NICE fever guidance for <5yos then do:
full blood count
blood culture
C-reactive protein
urine testing for urinary tract infection
consider
lumbar puncture in children of all ages (if not contraindicated)
chest X-ray irrespective of body temperature and WBC
serum electrolytes and blood gas
if amber features can still test urine, do bloods as above, LP if <1yo, in a child with a fever greater than 39°C and WBC greater than 20 × 109/litre
if in green group then no CXR or bloods
In children aged 3 months or older with fever without apparent source, a period of observation in hospital (with or without investigations) should be considered as part of the assessment to help differentiate non-serious from serious illness
When a child has been given antipyretics, do not rely on a decrease or lack of decrease in temperature at 1–2 hours to differentiate between serious and non-serious illness. Nevertheless, in order to detect possible clinical deterioration, all children in hospital with ‘amber’ or ‘red’ features should still be reassessed after 1–2 hours
immediate mx of child w fever in hospital - immediate requirement for fluid and what to give, 3 times for immediate IV abx (+ choice), when to give aciclovir, when to start O2, what else is urgently needed if giving fluids or starting immediate abx, how and when to control fever (and how not to)
Children with fever and shock presenting to specialist paediatric care or an emergency department should be:
given an immediate intravenous fluid bolus of 10-20 ml/kg; the initial fluid should normally be 0.9% sodium chloride or ideally a balanced crystalloid if available quickly
Give immediate parenteral antibiotics to children with fever presenting to specialist paediatric care or an emergency department if they are:
shocked
unrousable
showing signs of meningococcal disease
Immediate parenteral antibiotics should be considered for children with fever and reduced levels of consciousness. In these cases symptoms and signs of meningitis and herpes simplex encephalitis should be sought
for abx use cefotaxime + amox if <3mo or ceftriaxone if >3mo
Give intravenous aciclovir to children with fever and symptoms and signs suggestive of herpes simplex encephalitis
Oxygen should be given to children with fever who have signs of shock or oxygen saturation (SpO2) of less than 92% when breathing air
Children with fever who are shocked, unrousable or showing signs of meningococcal disease should be urgently reviewed by an experienced paediatrician and consideration given to referral to paediatric intensive care
tepid sponging and under/overdressing not recommended to control fever, but can give antipyretics (paracetamol or ibuprofen) if child appears distressed - note youre trying to alleviate the distress, not bring down the temp so only use as long as kid seems distressed and dont give both
home guidance for managing child w fever - antipyretics, 6 things to advise parents, 6 reasons for parents to re-seek advice
antipyretics as per guidance for in hospital mx
Advise parents or carers looking after a feverish child at home:
to offer the child regular fluids (where a baby or child is breastfed the most appropriate fluid is breast milk)
how to detect signs of dehydration by looking for the following features:
sunken fontanelle
dry mouth
sunken eyes
absence of tears
poor overall appearance
to encourage their child to drink more fluids and consider seeking further advice if they detect signs of dehydration
how to identify a non-blanching rash
to check their child during the night
to keep their child away from nursery or school while the child’s fever persists but to notify the school or nursery of the illness.
Following contact with a healthcare professional, parents and carers who are looking after their feverish child at home should seek further advice if:
the child has a fit
the child develops a non-blanching rash
the parent or carer feels that the child is less well than when they previously sought advice
the parent or carer is more worried than when they previously sought advice
the fever lasts 5 days or longer
the parent or carer is distressed, or concerned that they are unable to look after their child
You are the paediatric SHO and you have been called to A&E to see a child referred by the GP. Hannah is 8 months old and has had a fever for the past 24 h. Her mother tells you that Hannah has become lethargic and seems irritable, unable to settle - 8 dd (2:5:2 and 1 for rest):, hist (19Qs), exam 15 things, 10 ix
dd - 1 Serious bacterial infection, e.g. meningitis, septicaemia. 2 Localized infection, e.g. otitis media, pneumonia, UTI, gastroenteritis, osteomyelitis. 3 Viral infection: self-limiting URTI or specific infection (e.g. chickenpox) 4 Other systemic infection, e.g. malaria. 5 Inflammatory disorders, e.g. inflammatory bowel disease. 6 Autoimmune disorders, e.g. juvenile idiopathic arthritis. 7 Malignancy. 8 Kawasaki’s disease
hist - when did she become unwell? what were the temperatures? any systemic upset (irritable, lethargy, not responding to surroundings), any change in cry? any rashes? any D&V, cough, rhinorrhoea, pulling at ears, holding limbs in unusual position? feeding normally? wetting her nappies? obstetric and delivery history? any pmh inc things that could causes immunodef like HIV, sickle cell; any recent infections? are imms up to date? any foreign travel? anyone else at home or close contacts unwell?
examination - AVPU, pupil responses, temp and resp rate, signs of resp distress, signs of shock (pulse, BP, crt, periph temp); is skin pale, flushed, mottled?; is there a rash? any meningism or raised icp features? feel ant fontanelle, look for focal neuro signs, feel abdo, look for frog leg position or hot/swollen joints, ENT exam (save to last)
ix - LP if need to rule out mening and icp not raised; cultures, FBC, diff WCC, U&Es, CRP, urine sample for dip and MCS, resp virus swab (inc flu, COVID), CXR if resp signs, stool culture + calprotectin
Nathaniel is a 3-month-old Afro-Caribbean baby who is brought to A&E by his parents after developing a fever. They tell you that Nathaniel is off his feeds and is unusually sleepy. His crying has become high pitched - 4 dd, 12 hist, 11 exam, 8ix, 3mx
dd - Meningitis. 2 Encephalitis. 3 Other focal bacterial infection, e.g. pneumonia, UTI, otitis media. 4 Viral infection
hist - when/what was wrong first? what have temps been? any vomiting? any loc/convulsions? any rash/cough/dyspnoea or ear pulling? how much feed in last 24h? wet nappies? had other illnesses, any vaccinations? obs/labour history; any infectious contacts at home?
look for avpu, rash, behaviour eg drowsy, irritable; signs of dehydration, raised icp (ant font, unequal pupils, hypertens w bradycard (cushing), rarely papillo); kernigs, brudzinskis, lying with arched back; do resp and ent system exam
blood cultures and PCR, FBC, U&Es, blood glucose, MSU, rapid antigen test on blood/csf or urine, then when stable LP sending csf for cyto, micro, biochem
broad spectrum abx (with listeria cover if <1mo), iv fluid resus, dexameth
meningitis rash caused by what, LP indication x3, steroids (reason to give, how given, what age)
non-blanching rash” that everybody worries about as it indicates the infection has caused disseminated intravascular coagulopathy (DIC)
and subcutaneous haemorrhages.
NICE recommend lumbar puncture as part of the investigations for all children:
Under 1 months presenting with fever
1 – 3 months with fever and are unwell
Under 1 years with unexplained fever
Steroids are also used in bacterial meningitis to reduce the frequency and severity of hearing loss and neurological damage. Dexamethasone is
given if the lumbar puncture is suggestive of bacterial meningitis
meningitis mx kids - abx choice inc why not the normal one if <3mo, consider steroids x4 and what age not to give, 3 more things needed + 1 more abx to add and 2 reasons why
Antibiotics
< 3 months: IV amoxicillin (or ampicillin) + IV cefotaxime - note no ceftriaxone if <3mo as it displaces bilirubin from albumin binding sites, resulting in higher levels of bilirubin that accumulate in the tissues
> 3 months: IV cefotaxime (or ceftriaxone)
- Steroids
NICE advise against giving corticosteroids in children younger than 3 months
dexamethsone should be considered if the lumbar puncture reveals any of the following:
frankly purulent CSF
CSF white blood cell count greater than 1000/microlitre
raised CSF white blood cell count with protein concentration greater than 1 g/litre
bacteria on Gram stain - Fluids
treat any shock, e.g. with colloid - Cerebral monitoring
mechanical ventilation if respiratory impairment - Public health notification and antibiotic prophylaxis of contacts: ciprofloxacin is now preferred over rifampicin
also: If you’re treating empirically for suspected bacterial meningitis (either contracted abroad or from a patient who has spent extended duration abroad in recent history or have had prolonged or multiple exposure to antibiotics (within the past 3 months)) and you haven’t yet identified the causative organism, you need to take into account the possibility of penicillin-resistant Streptococcus pneumonia and add vancomycin. this is because because in the UK Pneumococcal penicillin resistant is exceedingly rare, whereas around many other parts of the world it is common enough that you can’t afford to not cover for it in the case of meningitis. This is largely driven by the over-use of penicillin-based antibiotics (both by prescribers and over-the-counter). once cultures and sensitivities are back you can stop the vanc
further mx (prophylaxis, who to inform) and potential complications (6) of confirmed meningitis
proph abx for all members of household and other close contacts (rifampicin - cipro now preferred)
notifiable disease - let consultant in communicable disease control know
complications: * Deafness: Due to inflammatory damage to the hair cells. All children with meningitis should have their hearing checked after recovery. * Cranial nerve palsies: Due to local vasculitis. * Cerebral abscesses: Cause rapid deterioration with a high fever and features of raised intracranial pressure. They require surgical drainage. * Epilepsy: May be caused by an abscess or local infarction. * Hydrocephalus: The presence of inflammation and exudates may block the reabsorption of CSF. A ventriculoperitoneal shunt may be needed. * Mental impairment: Permanent brain damage may result, although this is much less common with meningococcal rather than pneumococcal meningitis
what are contras to LP? (4)
Signs of raised intracranial pressure, e.g. papilloedema. * Cardiorespiratory instability. * Local infection at the site of the lumbar puncture. * Coagulation disorder or thrombocytopaenia
common LP contaminant
coagulase negative staph (CONS)
egs: S. epidermidis, S. capitis, S. hominis, S. warneri, and S. haemolyticus
3 markers of inflammation (inc what CRP levels tell you about therpay efficacy, and 4 reasons to use the newest marker)
crp: CRP is recommended over ESR to detect acute phase inflammation in patients with undiagnosed conditions because it is more sensitive and specific than ESR; concentrations change rapidly within the first 6-8 hours after injury, peak after 48 hours, and return to normal levels once the issue has resolve; CRP levels fall quickly once the cause of inflammation has resolved, CRP is a useful marker for monitoring disease activity: levels should decrease during the first 48 hours if treatment is adequate; increases in CRP concentrations during the first 48 hours suggest inadequate therapy - wait at least 24 hours to repeat
esr: fibrinogen released in blood causing RBCs to stick together which raises esr; Because the ESR depends on several proteins with varying half-lives, the rate rises and falls more slowly than do CRP concentrations; useful for select conditions, esp to do with bone, PMR, temp arteritis etc: presence of an ESR/CRP mismatch - you see this in SLE where a massive ESR and a modest CRP would push me towards disease activity rather than infection. You don’t tend to get mahoosive CRPs in SLE unless they have infection/serositis. Obviously the usual caveat of “never say never” in medicine applies here. You may also see a disproportionately high ESR in conditions like Sjogren’s or myeloma due to hypergammaglobulinaemia (polyclonal in Sjogren’s, monoclonal in haem issues); very unusual to have PMR, and even more so GCA when both ESR and CRP are normal (but can have it if only a mild raise in one or both)
procalcitonin: newer, more selective for bacterial cause: most often induced by bacterial infection; however, increases can also result from other causes, including severe viral infection, pancreatitis, tissue trauma, and certain autoimmune disorders; PCT levels halve daily when the infection is controlled, and levels correlate well with disease burden; rise over 2 tests suggests bacti infection and if not suggests other cause but not definite; main uses:
To differentiate systemic bacterial infection from non-infectious systemic inflammatory response syndrome (SIRS) (diagnostic marker) or suggests eg septic arthritis in face of equivocal aspirate vs rheumatic cause like reactive arth that would also inc CRP
* To ascertain the severity of illness of bacterial sepsis (prognostic marker)
* To monitor response to therapy of systemic bacterial infections
* To guide discontinuation of antibiotics during systemic bacterial infections - different guides exist based on different studies but eg withhold antibiotics for patients with procalcitonin values of ≤0.25 µg/L or stop antibiotics if procalcitonin levels decreased by ≥80% when the initial procalcitonin was >5–10 µg/L
* For cases of CAP and acute exacerbations of COPD to exclude a bacterial aetiology
markers of cell damage - 2 main ones and causes (7:5) and 3 more specific)
LDH is general marker of cell damage/death which may be raised in wide variety of conditions: liver disease, heart attack, anemia, muscle trauma, bone fractures, cancers, and infections (esp serious)
CK generally is muscle damage which can be from a direct damage to the muscle inc myopathies, or can result from eg infection causing damage; can be raised in various electrolyte abnorms and endocrine problems, due to medications, or due to surgery or exercise
other markers may inc GGT, AST/ALT, troponins etc
fever in returning traveller - 17 things to ask; exposures - freshwater 2 things, mosquito 2 things, animal bites 1 thing, tick bites 1 thing, rocky mountains 1 thing, drunk water 4 things, unpasteurised milk 2 things, cruises/air-con 1 thing, sex contact 6 things, healthcare 3 things, damp conditions or prison 1 thing; 14 ix
in DH ask if had chemoprophylaxis on recent trip
occupation may be relevant; any close contacts ill;
travel: when and for how long? move between countries? rural or urban? what kind of accom eg hotels, camping etc; what purpose, what activities while there; do pt have idea where may have come from - ask about tattoos, sexual activity, contact with sick person, drug use; what did they eat/drink? prophylaxis?
sexual history inc when last std check, ever positive?
freshwater - schisto, lepto; mosquito bites - malaria, dengue; animal bites -rabies; tick bites - lyme disease; rocky mountains - rickettsia
contaminated water - giardia, enteric fever, salmonella and campylobacter; unpasteurised milk - salmonella, listeria; cruises, air-con - listeria
sex contacts - HIV, hepatitis, chlam, gon, syph, warts etc
work in healthcare - TB, HIV, hepatitis
damp conditions or prison - TB
FBCs (differential white cell count)/U&Es/LFTs/CRP; if malaria then thick and thin blood films; HIV +/- viral hep test; cultures; PCR for some viruses; urine and stool for culture; CXR; if seizures or focal neuro then CT head; organomegaly then USS of these organs for eg abscess/amoeba
stats for causes in fever in returning traveller, infectious high fever w/o localising signs, neutrophil leucocytosis 3 things, if not how to interpret CRP
common + serious (30%): HIV, TB, malaria
common bacti (30%): Staphylococcus aureus bacteraemia, Streptococcus pneumoniae bacteraemia/meningitis, Neisseria meningitidis bacteraemia/meningitis
common viral (30%): EBV, flu etc
rare: haemorrhagic fevers, salmonella typhi or paratyphi, brucella, ricketssia, spirochaetes, dengue, amoebic liver abscesses, helminths
high fever without local symptoms or signs is often intracellular infection
in general CRP 100-130 is equivocal with over this more likely bacti, lower could also be either; can be useful to see how fast it is going up -> bacti tends to rise much quicker
if neutrophil leucocytosis then extracellular organisms more likely (bacti, spirochaetes, amoeba); if not then is CRP >100 (think eg salmonella, brucellosis), <30 (usually viral), 30-100 (almost anything)
eosinophilia algorithm (8 steps)
eosins >0.6x10^9/L (obtain previous FBCs if you can to see when it started)
if pt has atopy or urticaria identify provoking allergens, if asthma + skin/renal/nerve involvement consider churg strauss (ANCA test)
it no atopy/urti did it occur after pt took a drug? document history of drug exposure -> eosin, if poss discontinue drug and monitor eosin
if not then did occur after travel to developing country? if yes investigate for helminths, discuss with infectious disease; CXR, stool microscopy; if fresh water exposure then schisto so urine micro; if soil exposure then toxocara, stronglyoides so duodenal biopsy; if undercooked pork then trichinella or cysticercosis so CPK; if dogs then echinococcus so liver uss; if mosquitoes then filariasis so blood film, skin biopsy, opthalm assessment
if not then blistering skin rash? (biopsy for pemphigus or dermatitis herpetiformis)
if not then B symptoms? (lymphoma)
if not then renal/urine symptoms or purpura? (polyarteritis nodosa)
if not then abnormal CXR? (pneumo/haemothorax, sarcoidosis, lung helminths, drug induced pulm eosin)
if not consider rare causes: hypereosin syndrome, eosin leukaemia, coccidioidomycosis, hypoadrenalism
corticosteroids (5 metabolic actions, 7 anti-inflam actions (+effect on healing), how signalling through glucocort receptor works, 3 other effects
many actions inc: decrease glucose uptake by muscle/fat, inc gluconeogensis, inc protein metabolism, dec protein anabolism, redistribution of fat
also antiinflam actions inc: dec activity/influx of leucocytes, dec activity of monocytes, dec clonal expansion of T/B cells, switch from Th1 to Th2, dec pro-inflam cytokine production, dec eicosanoid production, inc release of antiinflam factors; will get reduced healing
bind to glucocorticoid receptor in cytoplasm which is bound to hsp90 (and other proteins), ligand binding causes hsp90 to dissociate and r’s to form homodimers which translocate to nucleus to transactivate/repress up to 1% of genome, thus drugs very broad spectrum with side effects; either binds to positive glucocorticoid response element within promoter, bind to negative GRE to displace tfs etc
also rapid non-genomic effects that arent well understood eg hydrocortisone rapidly inhibs neutrophil degranulation and GR antags dont stop this, same for IgE mediated mast cell degranulation and IV betamethasone reduces nasal itching after pollen applied within 10 mins, too fast to be genomic effects
10 corticosteroid side effects, whats given to minimise (inc indication)
oppurtunistic infection due to suppressed immune system, thinning of skin and impaired wound healing, oral thrush due to local anti-infection mechanisms suppressed when taken orally, osteoporosis due to severeal reasons including inc osteoclast and dec oestoblast activity, hyperglycaemia, muscle wasting, stomach ulcer, avascular necrosis of femoral head (rare, need hip replacement); long term use can get cushings syndrome + suppression of HPA so sudden withdrawal after >1week of use can result in acute adrenal insufficiency
other drugs given to reduce eg PPI and a bisphosphonate to protect bone
for bisphos: (In all men and women aged > 65 years who take corticosteroids of any dose for more than 3 months, including high dose inhaled corticosteroids or patients on 3/4 courses of prednisolone in a year.)
for PPI: if older, pmh of GI ulcer/bleed, or other meds/risk factors for upper GI problems present (antigoags/plats, SSRIs, NSAIDs, cav blockers)
steroid weaning
As a general principle, short courses of oral corticosteroids (less than 3 weeks) can be stopped abruptly as long as underlying symptoms allow. Gradual withdrawal should be considered for people whose disease is unlikely to relapse and who have:
Taken more than 40 mg oral prednisolone daily or equivalent for more than 1 week.
Taken repeated evening doses of corticosteroids.
Received more than 3 weeks of corticosteroid treatment.
Recently received repeated courses of corticosteroids (especially if taken for longer than 3 weeks), such as short courses repeatedly prescribed for the treatment of acute exacerbations of asthma.
A history of previous long-term therapy (months or years).
Other possible causes of adrenal suppression, such as excessive alcohol consumption or stress.
If stress, for example caused by infection, trauma, or surgery, occurs up to 1 week after stopping the corticosteroid, additional corticosteroid cover should be prescribed to compensate for any potential adrenal suppression.
During withdrawal, the dose of oral corticosteroids may be reduced rapidly down to physiological doses (about 7.5 mg of prednisolone or equivalent (as this is roughly equiv to normal physiological dose of 10mg/m^2 hydrocortisone a day ie should prevent adrenal suppression) and reduced more slowly thereafter.
Unlikely to have adrenal suppression if less than 2-3 weeks course even higher doses, and so generally no need to wean (or fast taper eg 25% per day); nevertheless be wary of adrenal insufficiency sx
Normal secretion generally takes 6-8 weeks to resume but may take 6-12mo; different tapering plans and no strict rules could eg wean to 10mg/m^2 hydrocort a day over eg 4-6 weeks or as sx allow then by a further 10-20% ie initially 2mg/m^2 every 1-2 weeks; when at physiological dose switch from dex/pred to hydrocort, shorter half life may help adrenal function recover
lethargy/depression suggests go back up and switch to slower wean over eg 6 months Check early morning serum cortisol 24-48 hours after stopping hydrocortisone - if adrenal insuff present restart and get endo advice for prolonged wean, and if borderline result seek advice likewise; for one year after still have clinical suspicion for adrenal crisis as gland function may not be fully recovered even with normal morning levels
3 common protective cellular pathways
stress kinase pathways activated by wide range of factors eg osmotic stress, oxidative stress, heat, UV, DNA cleavage) which activate heterodimeric transcription factors eg AP1 that re-programme transcription which may lead to shutdown of protein synthesis, apoptosis or necrosis depending on additional factor
heat shock response is reaction to injury in all living cells where stresses cause dissociation of cytosolic heat shock factors (proteins) from complexes which normally keep them inactive, these HSFs translocate to the nucleus and suppress transcription of some genes but promote HSPs, chaperone proteins which refold partially denatured proteins to allow cell to maintain function: HSPs thus responsible for preconditioning where cells exposed to minor injury become resistant to more major stresses
unfolded protein response (ER [protein] in active cell can reach 100mg/ml, which can allow unwanted precipitation/aggregation of proteins unless folded correctly and chaperoned), this process ensures rate of protein synthesis doesn’t exceed cells capacity to complete the folding process by activating signalling cascades that increase synthesis of folding chaperones, enhance proteasomal protein degradation and slows translation; UPR is usually reversible and part of process called ‘host cell shut down’, a primitive reversible response that acts within minutes to suppress DNA/RNA synthesis and inhibit many enzyme-catalysed reactions
apoptosis
intrinsic pathway: activated when the cell undergoes stress from the inside due to various factors such as DNA damage from x-ray or UV light exposure, chemotherapeutic agents, hypoxia, the accumulation of misfolded proteins inside the cell as seen in conditions such as Alzheimer’s disease, Parkinson’s disease, or Huntington disease, among others. When the cell undergoes stress, cytochrome c leaks from the intermembrane space of mitochondria into the cytosol, which leads to the activation of caspases 9. The regulation of this pathway is governed by the Bcl-2 and TP53 genes
extrinsic pathway: triggered when the cell receives death signals from the other cells, ultimately activating caspase 8; TNFa is main extrinsic trigger
Initiator caspases include caspases 2, 8, 9, and 10. When activated, the initiator caspases activate the effector caspases.
Effector caspases encompass caspases 3, 6, and 7. Active effector caspases cleave several proteins in the cell, leading to cell death and, ultimately, phagocytosis and removal of cellular debris
types of necrosis
Coagulative necrosis: Ischemia in most organs except the brain can lead to coagulative necrosis. In this type of necrosis, the cell architecture remains preserved. Under the microscope, the cells appear anucleate, eosinophilic, with preserved structure. Eventually, the dead cells are cleared by phagocytosis and leukocytes
Liquefactive necrosis: This morphology is most commonly observed in the central nervous system as less connective tissue and many digestive enzymes present. The dying cells are digested by hydrolytic enzymes and hence lose their structural integrity and turn into a viscous mass. This is also typical of bacterial, or sometimes fungal, infections because of their ability to stimulate an inflammatory response
Caseous necrosis: The term caseous means “cheese-like,” which refers to the whitish appearance of the necrotic area. This necrosis takes place in tuberculous infection, and the necrotic area is surrounded by a granuloma
Gangrenous necrosis: This is not a morphological pattern but rather a clinical term for ischemic necrosis of the limbs. It has two types i) dry (ischemia leading to coagulative necrosis), and ii) wet (ischemia with superimposed bacterial infection leading to liquefactive necrosis)
Fat necrosis: This type of necrosis occurs in acute pancreatitis. The release of pancreatic enzymes leads to liquefaction of the fat cells in the peritoneal cavity. These liquified fat cells then combine with calcium and are identified as chalky white areas. This process is referred to as saponification
Fibrinoid necrosis: This type of necrosis occurs in blood vessels due to the deposition of immune complexes in blood vessel walls leading to leakage of fibrin
inflammation (activating step, neurogenic inflam (inc 2 things released) dermatographic urticaria is what and treated by which 2 things, factor XII activation (by what, 4 things it produces, what the first 2 products produce), 2 cells that arrive later
PAMPs and DAMPs bind to PRR on macros, DCs, mast cells in tissue which activates them; lysis of host cells releases inflam mediators like atp;
neurogenic: stimulating nerve results in APs along central trunk up to brain, and along other branches from central trunk to give inflam; these branches release calcitonin gene related peptide CGRP and substance P, which directly cause vasodilation and SP is potent activator of mast cell degranulation which leads to local production of histamine
dermatographic urticaria (2-5% pop) is condition where triple response is exaggerated, is largely idiopathic and treated with H1r antagonists and the monoclonal antibody omalizumab which recognises IgE and acts to decrease mast cell activation
factor XII activated by contacting negative substances like collagen, becomes XIIa which produces thrombin (intrinsic pathway), plasmin, fibrin and bradykinin (activates kallikrein); first two hydrolyse C3 to produce C3a/b thus complement, coagulation, fibrinolytic, and kinin systems interact; complement (inc C3a/5a activating mast cells)
neutrophil migration + monocyte migration later attracted by chemotactic agents released by macros
histamine (inc what 4 cells its in), 3 mast cell receptors and common pathway for inducing degranulation, 4 histamine receptors
2-(1H-imidazol-4-yl)ethanamine; formed from histidine by histidine decarboxylase and found in mast cells, basophils, enterochromaffin-like cells (in gut) and histaminergic neurons
increase in cellular [Ca] causes degranulation: C3a/C5ar are Gi coupled with bg subunit activating PLCbeta, inducing intracellular Ca release via IP3; SP primarily induces via receptors which are Gq coupled, again acting via PLCbeta; allergens induce cross-linking of IgE with high affinity FceRI receptor which induces phospho of adapter protein linker for activation of T cells LAT and that causes activation of PLCgamma (IP3->Ca)
4 GPCR receptors; H1 -> Gq - PLCbeta - IP3/DAG/PKC (important for inflam); H2 - Gs - cAMP up (gastric acid); H3 - Gi - cAMP down (inhib autoreceptor in CNS); H4 - Gi - cAMP down (chemotaxis/cytokine release); so get smooth muscle contraction (ileum, bronchioles, uterus), blood vessel dilation via eNOS, itching by H1 activation of pruritoceptors, H1 triple response, H2 increase HR/gastric acid secretion
anti-histamine and anti mast cell action - 4 drugs + H1r antags first gen (and problems), second gen (and problems), third gen
sodium cromoglycate is mast cell stabiliser with unclear mechanism but observed to decrease Ca influx, a proposed mechanism is inhib of an inwards Cl conductance required to maintain -ve enough PM pot to sustain Ca influx
raising cAMP also stops degranulation so beta2 agonists (salbutamol, formoterol) and PDE inhibitors (theophylline) in treatment of asthma helps, though main affect via bronchodilation; omalizumab stops by stopping IgE binding to FceRI
h1r antags - classical antihistamines, used to treat histamine inflam; first gen like mepyramine, diphenhydramine (benadryl) permeated BBB and caused drowsiness so not suitable for systemic use, though still used topically for insect bites, and in some cold/flu remedies to aid sleeping; 2nd gen couldnt cross BBB so terfenadine, big in the 1980s but found it inhibited Kv11.1/hERG resulting in long QT interval and possibly sudden cardiac death: terfenadine is prodrug metabolised to active fexofenadine by 3A4 isoform of cytochrome P450 so enhanced risk of death if this enzymes inhibited, and this enzyme inhibited by grapefruit juice and many drugs; every new drug now screened for activity against hERG; 3rd gen are non-drowsy, lack cardiac side effects and include fexofenadine and loratadine; theyre used to treat hay fever, allergies and uticaria
bradykinin (formed by what, inactivated by what, B1 and B2r coupled to what, difference in expression, causes production of what two things which increase what two signalling molecules and effect of this), other affect of activating Br, role of C1Ei and 2 types of HAE, 2 things that treat it)
bradykinin first identified as slow contractor of ileal smooth muscle; formed by kallikrein on kininogens (can be HMW or LMW); hageman factor (factor XII) activated by contacting -ve charged surface (collagen, BM, LPS) after leaking out of blood vessels during inflam, then converts prekallikrein to kallikrein which clips HMW kininogen to bradykinin and LMW kininogen to kallidin; bradykinin further clipped to inactivate by eg kininase 2 aka ACE
B1r and B2r both Gq coupled with B1r upregulated during inflam by cytokines like IL1, B2r constitutively expressed and potently activated by bradykinin/kallidin; activating these r in vascular endothelium causes increased Ca which activates cytosolic phospholipase A2, causing prostacyclin (PGI2) production and eNOS activity; PGI2 and NO diffuse to smooth muscle, increase cAMP and cGMP respectively and mediate vasodilation (ACEi cause more bradykinin which thus causes vasodilation via this mechanism); activating Br also drives nociception (activates and sensitises) as Gq -> PKC -> phospho of ion channels involved in pain sensation
kallikrein inhibited by C1-esterase inhibitor and in hereditary angioedema (HAE) mutation in C1INH causes excessive bradykinin leading to periods of severe/painful swelling; type I HAE compromises synthesis/secretion, type II allows inactive HAE to be produced; ACEi angioedema has 5x higher prevalence in african americans, possibly linked to variation in genes that control immune system; ecallantide is inhibitor of kallikrein that can treat HAE, as is recombinant C1INH, may also treat ACEi angioedema
prostanoids (why named prostaglandin, how COX makes prostaglandins - 2 reactions, difference in COX expression, what the 2 in the names means, then how specific prostaglandins made)
named prostaglandin as first discovered in semen (from prostate gland); COX makes prostaglandins from arachidonic acid in 2 reactions, first acid cyclised and oxygenated to form endoperoxide PGG2, then hydroperoxyl reduced to form PGH2; COX1 constitutively expressed in many types of cells, COX2 also to small extent though mainly induced by inflam
cell specific enzymes then produce specific prostaglandins or thromboxanes from PGH2 eg PGE2, PGI2, TXA2 (2 means 2 C=C bonds, if eicosatrienoic acid instead at first step get PGE1 etc and if eicosapentanoic acid then PGE3 etc); PGE/I2 tend to be produced locally by tissues/blood vessels, PGD2 mainly mast cells, and PGE2/TXA2 mainly by macros in chronic inflam (the specific enzymes are called eg PGD synthase)
innate response overview (inc roles of mast and dendritic cells and 3 things that activate mast cells)
Innate immunity is the first immunological, non-specific mechanism for fighting against infections, to eliminate initial cause of cell injury, remove damaged/necrotic tissue and initiate repair; has phagocytosis, cytokine secretion and complement activation; leucocytes and acute inflammatory exudate (soluble factors) recruited to site of injury and may eliminate pathogen, and in more serious cases acute phase (systemic) responses occur and consist of fever, neutrophilia (increased numbers of circulating neutrophils) and increase in acute phase proteins in plasma
mast cells: key role in inflam, containing mediators of inflam eg histamine, with function to rapidly induce inflam and can degranulate within seconds of activation by a wide range of factors including allergens (IgE), danger signals (PAMPs/DAMPs) and complement components (C3a/C5a), and these cells are resident under epithelial surfaces along with macrophages where they function as sentinel cells to sense tissue damage
dendritic cells bridge innate and adaptive systems, recognising pathogens at site of infection in periphery and carrying this info to the draining lymph nodes to initiate the adaptive response
acute-phase proteins (activation, 13 positive (and function), 4 negative)
After stimulation with proinflammatory cytokines (including IL-6), Kupffer cells produce IL-6 in the liver and present it to the hepatocytes. IL-6 is the major mediator for the hepatocytic secretion of APPs. Synthesis of APP can also be regulated indirectly by cortisol. Cortisol can enhance expression of IL-6 receptors in liver cells
acute phase proteins that are produced more include CRP (opsonisation - bind dead/dying cells and bacteria to activate complement), MBL, complement, ferritin (dec fe availability), caeruloplasmin (oxidise iron to facilitate ferritin binding), serum amyloid A (recruit inflam cells, induce enzymes to degrade ecm), haptoglobin (bind haem so less iron available), fibrinogen, prothrombin, plasminogen-activator inhibitor, hepcidin (dec fe availability), a2 macroglobulin (inhib thrombin and plasmin), a1 antitrypsin (reduce inflammation)
produced less: albumin, transferrin, antithrombin, C3 levels often down due to increased turnover but production actually increased
neutrophil left shift
Left shift or blood shift is an increase in the number of immature cell types among the blood cells in a sample of blood. Many (perhaps most) clinical mentions of left shift refer to the white blood cell lineage, particularly neutrophils
Less commonly, left shift may also refer to a similar phenomenon in the red blood cell lineage in severe anemia, when increased reticulocytes and immature erythrocyte-precursor cells appear
In any acute inflammation, an increase in neutrophils is often seen. Infection most common but also increases may be seen after a heart attack (or other infarct), necrosis, exercise, anxiety, and other stressors.
lymphopenia due to infection (and 2 means by which steroids cause)
Seven different mechanisms were involved in lymphopenia caused by viral infections, including cell death, elevated cytokines, chemokines and growth factors, inhibition of lymphopoiesis, lymphocyte trafficking, up-regulated expression of co-inhibitory molecules, metabolic disorders (lactic acidosis can suppress proliferation of lymphocytes) and elevated glucocorticoids.
one major part is lymphocytes migrating from blood to tissue eg sequestration in lungs during viral lung infection like COVID or RSV; rapidly correct the low levels when infection resolves as they reenter blood
Corticosteroids cause lymphopenia via two mechanisms: in the short term, they shift lymphocytes out of the circulating pool; over the long term, they decrease lymphopoiesis.
Severe infection (bacterial or viral) can cause lymphopenia because lymphocytes move from the circulating pool into the tissues. Endotoxemia and septicemia can lead to lymphopenia, mostly as a result of the increase in corticosteroids that occurs in response to inflammation.
phagocytes (neuts (2 things they do), macros - inc subtypes and the 4 receptor types they have)
neutrophils most abundant, mobilised to sites of infection and phagocytose microorganisms and then die, being very short lived, they can also extrude DNA forming neutrophil extracellular traps NETs that trap microbes, which is seen as pus
macrophages resident in CT, lining of tracts, and liver, engulf microbes and dispose of cell debris with two proposed effector subsets: M1 secrete cytokines/pro-inflammatory mediators to stimulate acute inflam response, M2/alternatively activated are associated with tissue repair and killing/expulsion of parasites, though this two subset model is probably an over-simplification, have lectins/scavenger receptors/complement receptors/TLRs with first 3 recognising bacti/fungi (eg LPS) to trigger phagocytosis, latter binds PAMPs, leading to phospho of inhibitor of NFkB to induce cytokine production
NK cells (what they are, 2 ways theyre activated including important eg of one)
along with complement and phagocytes are 3rd major part of innate system, circulating in blood in partially activated state to facilitate immediate response and can move into affected tissue and proliferate; they’re especially important to viral infections where they kill infected cells and maintain/increase state of inflam
NKs recognise infection/cell damage through receptors signalling: loss of molecules normally expressed (missing-self), expression of molecules induced in stressed cells (induced-self) with response dependent on balance between activating and inhibitory receptors with activating receptors detecting perturbations in infected/stressed cells; inhibitory receptor signals dominate in healthy cells, major signal from MHC class I molecules present on the surface of most healthy cells and which present peptide fragments derived from cytosolic pathogens (eg viruses) to T cells, signalling the cell should be killed, thus viruses evolved means to prevent MHC class I expression and NKs see this missing-self and activate; induced self during infection/stress relies on cells expressing surface ligands for activating receptors on the NK, usually requiring signals from several different kinds of activating receptors
NK cell functions (3 things that virus infected cells do, how NK cells and macros interact, what NK cells do, how NK cells and DCs interact)
virus infected cells produce cytokines (type I IFNs) that encode an anti-viral state by inducing resistance to viral replication in surrounding cells, increasing expression of ligands recognised by NK receptors and activate NKs; local macrophages produce cytokines (CXCL8 and IL-12) that recruit and activate NKs and cause their proliferation; activated NK cells produce cytokines (IFNgamma) that activate macrophages and upregulate their killing capacity; together these steps ensure NKs induced to kill virus-infected cells and macrophages activated to phagocytose viral particles and infected cells the NKs killed
kill target directly by releasing cytoplasmic granules containing perforin which forms pores in PM allowing apoptosis inducing granzymes into cell; antibody dependent cell cytotoxicity where NKs have receptors for Fc portion of antibodies and kill cells bound to the antibodies with signalling through the Fc receptor strong enough to activate the NK by itself;
when NK cells outnumber DCs can kill them, if dont (ie innate response insufficient) then drive DCs to mature/migrate
interferons (what they are, three main types, where produced and what they do, what therapeutic uses they have, 2 of the general mechanisms they use to achieve their goal)
group of protein signals made and released by host cells in response to viral infection
type of cytokines
IFN 1a/b produced by fibroblasts, macrophages, lymphocytes, endothelial cells and more and cause target cells to express proteins that make it hard for viruses to replicate in them; ifn 1a used for HBV/HCV and ifn 1b for MS
IFNg released by CD8 and Th1 cells, blocking Th2 response and driving greater Th1 response
among various mechanisms, IFNs increase p53 activity which promotes apoptosis in virus infected cells, and causes MHC class I and II expression to increase
Hemophagocytic lymphohistiocytosis (HLH) - 2 main types, (5 sub-causes for 2nd), 9 sx, 5 ix + other way to diagnose, mx)
primary - genetic mutations fully eliminate the function of cytotoxic T cells and NK cells
secondary - external triggers like infection, malignancy, rheumatologic disease, postallogeneic hematopoietic stem cell transplantation (HSCT), drug hypersensitivity etc; commonest cause is EBV infection (or in adults, reactivation of EBV when immunosuppressed); how these triggers cause not fully clear but linked to overproduction of cytokines; secondary is still also usually in children
common sx inc fever (oft high, persistent), organomegaly, lymphadenopathy, neurologic involvement (more often seen in pediatric HLH and includes seizures, meningismus, peripheral neuropathy, cranial nerve involvement, ataxia, dysarthria, lethargy, encephalopathy, and coma), pancytopenia, and coagulopathy (hemorrhage, petechiae, ecchymosis, purpura, and disseminated intravascular coagulation); edema, rashes, and gastrointestinal symptoms like diarrhea, nausea, vomiting, and abdominal pain may also be seen.
acute phase proteins all up except fibrinogen down, triglycerides up, cytopenia; scoring system for likelihood, biopsy of marrow/spleen/LNs may demonstrate
presentation overlaps with sepsis and must consider if sepsis not responding to mx; two may co-exist (sepsis may trigger HLH); clues pointing to HLH inc organomeg, v high ferritin, cytopenia, hypofibrinogen, thrombocytopenia without DIC; DRESS may also overlap, as can atypical infections of various kinds, and in neonates storage diseases or liver failure
mx is with immunosuppression
soluble inter-related plasma protein systems
complement system cascades activated by numerous mechanisms, result in opsonisation, membrane attack complex formation and generation of anaphylatoxins
fibrinolytic system via Hageman factor results in generation of plasmin, a protease which degrades fibrin into chemotactic products for neutrophils and activates complement C3
kinin system via Hageman factor results in bradykinin generation to increase vascular permeability, vasodilation, smooth muscle contraction and activates complement C3 and C5
clotting system via Hageman factor via thrombin to convert fibrinogen into fibrin and fibrinopeptides, former to form a clot to limit spread of infection and latter to induce vascular permeability and neutrophil chemotaxis, thrombin also cleaves C3/C5 into C3a/C5a; Hageman factor stimulated by tissue damage
complement system (what it is inc where made and how distributed, 7 things it does, how C3 works inc its 2 subunits; complement receptors inc 2 CR1 roles and how C5a helps
made of ~30 soluble and membrane associated proteins mainly made in liver and widely distributed in tissues and fluids as zymogens with many components involved in sequential proteolytic cleavage reactions to generate enzymatic products in an explosive amplification
activates inflam, opsonisation of microbes and lysis of target cells, clearance of immune complexes and apoptotic cells and stimulating adaptive responses, plus chemotaxis; facilitates uptake and killing of pathogen by phagocytic cells, via complement receptors
C3 is key: unusual internal thioester bond which is exposed upon cleavage in the C3b fragment and can react with hydroxyl/amino groups, with subsequent covalent linkage to pathogen opsonising it for phagocytosis and leading to generation of more C3b; C3a is an anaphylotoxin and stimulates local inflam
complement receptors recognise proteolytic cleavage derivatives of C3, with CR1/3 esp important for phagocytosis of complement tagged bacteria: CR1 binds directly to C3b; C5a (through C5a receptor) delivers additional signal necessary for macrophages to begin phagocytosis and promotes neutrophil chemotaxis; CR1 also highly expressed on erythrocytes and binds C3b attached to antibody/antigen immune complexes to remove them from the blood for clearance in the liver, and individuals with low CR1 levels suffer from immune-complex disease
5 chemotactic agents
besides CXCL8, there are lipids derived from arachidonic acid, C5a, certain peptides made by degradation of bacteria, and other CXCs
alternative pathway for complement + MAC formation and what its effective against
first to act, reliant on spontaneous conform changes in C3 to expose thioester group, which in water usually leads to generation of C3H2O, allowing it to associate with factor B, which then becomes susceptible to the serine protease factor D; Bb remains associated to form C3(H2O)Bb, itself a protease (called aqueous/fluid phase C3 convertase) which cleaves C3 into C3a/C3b, role to produce enough C3b that some will attach to activating surface of pathogen (microbial surfaces are activating in general as they lack regulatory mechanism to deactivate complement), then once C3b bound can bind factor B and generate surface bound C3bBb, the alternative pathway C3 convertase which can generate more C3b bound to membranes and soluble C3a; surface bound C3b acts as an opsonin and provides +ve feedback loop
instead of binding to surface C3b can remain attached to C3bBb forming C3b2Bb, the alternative C5 convertase which cleaves C5 to start the formation of the membrane-attack complex: binding of C6/7 to C5b allows C7 to insert into lipid membranes and binding of C8 to C5b67 allows insertion into membrane and subsequent polymerisation of C9 subunits to form membrane pore, effective against many gram negative bacteria and enveloped viruses
lectin pathway
complement, second to act, activated by mannose binding lectin (MBL) and M,H or L -ficolin; MBL is a collectin, comprised of collagen and lectin domains and is also a soluble pattern recognition receptor that binds the close-knit arrays of mannose/fucose residues found on microbial surface of bacteria, yeast, fungi and some viruses
MBL and ficolins circulate in plasma associated with 2 serine proteases: MBL-associated serine protease (MASP) 1 and 2; upon binding pathogen surface, MASP activity is initiated, cleaving C4 and then C2; C4 has internal thioester bound and C4b can attach to pathogen surface, joined by C2a to form C4bC2a, the classical C3 convertase which begins cleaving C3
classical complement pathway
activated if pathogen surface is recognised by antibody or c-reactive protein, which recognises bacteria, fungi, yeast and parasites; binding of antibody to surface exposes binding site for C1q present in Fc region of some antibody isotypes; C1q binds to several Fc regions and undergos conform change to activate C1r/C1s subunits; C1s cleaves C4 to expose thioester group allowing covalent attachment of C4b to pathogen surface; activated C1 associates with and cleaves c2, depositing C2a on C4b to form C4bC2a which cleaves C3 depositing C3b on the surface; membrane associated C3b generated by classical and lectin pathways can utilisie alternative pathway ampllfication loop by binding factor B; classical C3 convertase can associate with C3b to generate C4bC2aC3b, classical C5 convertase
5 complement deficiencies - defects in C1-4, defects in C3a/b, deficiency of Factor I/H, deficiency in C5-9, reduced GPI synthesis)
early components of classical pathway facilitate clearance of soluble immune complexes by coating them with C4b/C3b so defects in C1-4 fail to clear these and have immune-complex disease
activated C3 is important opsonin for bacteria phagocytosis so defects in it or its activation result in susceptibility to pyogenic (pus-forming) infections eg Staphylococcus/Streptococcus; depletion of C3 due to uncontrolled alternative pathway activation (FactorI/H deficiency) leads to similar susceptibility;
complement mediated lysis is most effective defence against Neisseria so individuals with deficiencies in MAC components C5-9 suffer from recurrent Neisseria infections
DAP and protectin are GPI anchored proteins so reduced GPI synthesis gives reduced expression of DAP/protectin on RBCs causing autoimmune-like conditions such as paroxysmal nocturnal haemoglobinuria due to complement mediated lysis of RBCs
triggers for inflam - 3x sentinel cells and how they sense damage, 4 broad things they release, 5 specific cytokines and their role
sentinel cells (mast cells, macrophages, dendritic cells) resident in tissues help sense damage/infection by expressing pattern recognition receptors which recognise molecules associated with pathogens: pathognen associated molecular patterns (PAMPs) or cellular damage damage associated molecular patterns (DAMPs), with these cells then releasing cytokines and other inflam mediators
mast cells contain granules of preformed inflam mediators (eg histamine, heparin, leukotrienes, prostaglandins); in addition to phagocytosis, macrophages produce range of cytokines (inc endogenous pyrogens which induce fever) that have local effect on vascular endothelium and systemic effects such as IL-6 and acute phase protein response; macrophages also synthesise prostaglandins and leukotrienes; inc dilation and permeability and activation of endothelium results in recruitment of acute inflam exudate
IL-1beta activates vascular endothelium and lymphocytes and increases access of effector cells locally as well as systemically promoting fever and IL-6 production
TNF-alpha activates endo and inc its permeability leading to inc entry of IgG, complement and cells and inc lymph drainage locally, as well as systemically promoting fever, mobilisation of metabolites and shock
IL-6 inc antibody production and activates lymphocytes as well as inducing acute phase protein production and fever
CXCL8 is a chemotactic factor recruiting neutrophils, basophils and T cells
IL-12 activates NK cells and induces differentiation of CD4 T cells into TH1 cells
4 stages of neutrophil recruitment to site of inflam (+ what else is recruited and how long it takes) (and disease when mutation affects neutrophil oxidative burst, what enzyme affected and result)(and LAD)
chronic granulomatous disease NADPH oxidase means neutrophils dont make superoxides, bacti not cleared and granulomas form
neutrophils/monocytes recruited either by binding to adhesion molecules on endothelial cells and by chemo-attractants produced in response to infection; first step is rolling adhesion/weak tethering is thrombin (from blood) and histamine (from mast cells) induce P-selectin on endothelial cells, released from intracellular stores called weibel-palade bodies; E-selectin appears 1-2 hrs later, induced by IL-1 and TNFa, then the selectins bind to glycoprotein ligands (on neutrophils in low affinity interactions broken by the force of blood flow, resulting in neutrophils rolling along endothelium
tight adhesion results from interaction between integrin lymphocyte function adhesion antigen 1 (LFA-1) binding to intercellular adhesion molecules ICAMs on the endothelium, with initial weak adhesions which strengthen due to conform change in LFA-1 resulting in high affinity binding state due to signalling through chemokine receptors eg CXCL8
extravasation follows with leukocytes squeezing between gaps in endothelial cells into tissues due to interactions between LFA-1 and CD31 on endothelial cell, with neutrophils secreting enzymes like elastase that degrade the basement membrane; neutrophil then follows gradient of CXCL8 (secreted by active macrophages) to site of infection, with the CXCL8 sticking to extracellular matrix to form this gradient
leukocyte adhesion deficiency is rare immunodeficiency caused by defect in recruitment of neutrophils: LAD1 caused by defect in CD18, the beta chain subunit of LFA1, and it results in recurrent life threatening bacterial infection in infants
monocytes also recruited but takes 24hrs
TNFa and sepsis (local role, when is too much released, 2 consequences)
bloodclotting caused by local expression of TNFa prevent pathogens entering blood and spreading; however, if pathogen is widespread (severe skin burns) infection can spread with endotoxins such as LPS provoking widespread TNFa release; when pathogens enter bloodstream sepsis occurs, macrophages in liver/spleen secrete TNFa into circulation with potentially catastrophic consequences as the vasodilationtriggered by TNFa leads to septic shock, loss of BP and heart failure; the TNFa also triggers clotting in small vessels throughout body (disseminated intravascular coagulation) with failure of major organs
3 functions of antibodies
antibodies work via neutralisation (blocks biological activity of target molecule), opsonisation (coat antigen and interact with receptors on phagocytes allowing more efficient recognition of antigen) and complemet activation (recruits complement to antibody-coated antigen, possibly causing direct lysis or facilitating complement opsonin activity)
T cell intro - where made and where mature, what happens with TCR, what TCR recognises (and how theyre made), MHC classes and how these link to T cells
arise in bone marrow, mature in thymus where genes encoding TCR rearrange to generate clones with different specificities
TCR only recognises degraded proteins complexed with MHC, antigen processing by antigen presenting cells generating these peptides for display; 2 major classes based on function, accessory molecule expression and type of MHC presenting; MHC class I on most cells (except eg RBCs) and associates with peptides produced in cytosol, and complex recognised by class I restricted T cells expressing co-receptor CD8, maturing into cytotoxic T cells and important in targeting virus infected/tumour cells; MHC class II (using external peptide) restricted T cells express CD4 and mature into T helper cells to help B cells/cytotoxic T cells; class II primarily on professional APCs; both types also produce cytokines
naive T and B cell activation
T: in peripheral/secondary lympoid organs, where nodes/spleen designed to optimise interaction between APC and T/B lymphocytes: lymphatics drain fluid containing antigens and dendritic cells from tissues and collect via afferent vessels to pass through macrophage lined sinuses where antigens/microbes captured to stop passing into the blood; lymphocytes enter node through specialised high endothelial venules, dendritic cells from periphery having captured antigens, naive T cells then survey antigen displayed on MHC molecules of dendritic cells and those which recognise the antigen/MHC complex retained and stimulated to differentiate into effector T cells
B: cells with receptors specific for antigen helped by activated T effector cells and stimulated to produce antibody; some B cells concentrate into areas around follicular dendritic cells (not to be confused with dendritic cells), guided by chemokine CXCL13; FDCs use receptors for IgB and complement to trap antigens in antigen/antibody/C3b complexes, don’t process it but do hold it for long periods of time on their surface for screening by B cells with those cells that have highest affinity for antigen preferentially induced to proliferate in process called affinity maturation; localisation of APCs, B cells and T cells maximises chance of B-T cell co-operation
antibody structure and classes
pairs of heavy/light chains held together by covalent disulphide bridges and non-covalent forces, with both chains constructed from structurally related Ig fold domains; light chains have 1 constant and 1 variable domain and present as 1 of 2 types (kappa 2/3 and lambda 1/3); heavy chains have 1 variable and either 3 (IgG, IgA, IgD) or 4 (IgE, IgM) constant domains
5 main classes of antibody (IgA/D/E/G/M) distinguished by heavy chains denoted alpha/delta/epsilon/gamma/mu with the heavy chain determining the function of the antibody
hinge region gives molecule flexibility to interact with antigen, with flexibility also present at the V-C junction and likened to ball-socket joint
antigen binding site: formed by interaction between light/heavy variable domains, with variation concentrated in 3 complementarity determining regions (CDRs)
IgG subclasses
4 distinct subclasses. The evolution of IgG subclass switches is regulated by interaction with T cells and follows a 1-way direction (IgG3 → IgG1 → IgG2 → IgG4)
the response to proteic antigens is prevalently mediated by IgG1 and IgG3, while IgG2 mediates the response to polysaccharide antigens; IgG1 is the most abundant and is biggest contributor to total IgG
IgG3 and IgG1 exhibit the most efficient activation of the classical complement cascade. Under conditions of high antibody titer or high antigen density, IgG2 is capable of activating complement as well, but IgG4 is generally incapable
as a result of above IgG2 is most important for dealing with encapsulated bacteria and its deficiency incs risk if strep pneumoniae, Hib, and neisseria infections (matures late hence why children <2yo more vulnerable to encapsulated bacti infections)
IgG def presents as recu OM, sinusitis, pneumonia
antibodies and the placenta
IgG is the only antibody class that significantly crosses the human placenta. This crossing is mediated by FcRn expressed on syncytiotrophoblast cells. There is evidence that IgG transfer depends on the following: (i) maternal levels of total IgG and specific antibodies, (ii) gestational age, (iii) placental integrity, (iv) IgG subclass, and (v) nature of antigen, being more intense for thymus-dependent ones
In some situations, such as mothers with primary immunodeficiencies, exogenous IgG acquired by intravenous immunoglobulin therapy crosses the placenta in similar patterns to endogenous immunoglobulins and may also protect the offspring from infections in early life. Inversely, harmful autoantibodies may cross the placenta and cause transitory autoimmune disease in the neonate
maternal antibody levels then gradually wane, generally gone by 6mo but sometimes persisting slightly beyond this
affinity maturation and isotype switching
in a primary response, B cells with receptors for antigen internalise, process and present it to T helper cells which then activate B cells to produce antibody, usually of relatively low affinity; antibody binds and clears antigen, so only B cells with highest affinity continue to capture and present antigen to T helper cells, and thus are stimulated further to proliferate and predominate; is a fast evolution system, doing in days what would take classic evolution thousands of years, and enables immune system to keep up with rapidly mutating pathogens
mature naive B cells initially produce IgM/IgD isotypes, only types produced at same time; isotype/class switching then allows change in constant region isotype; AID (activation induced cytidine deaminase) made only by stimulated naive cell, targets switch sequence in C gene to which cell will be switched; patients lacking AID only make low affinity IgM - hyper-IgM syndrome; isotype switched to determined by cytokines expressed by Th cells eg IL4 IgE, ifng IgG1
opsonisation by antibodies (what it is, 2 things that bind the bound Ig, what macros/neuts express, IgM main thing that it activates and how it is cleared, and ADCC [4 cells that express FcgRIII, how ADCC activates in 2 diff kinds of cells)
coating surface of antigen to enhance phagoctyosis, with receptors for Ig or complement components (C3b) able to bind antibody/complement opsonised antigen; macrophages and neutrophils express Fcg receptors which efficiently recognise Fc of IgG, particularly IgG1; receptor engagement leads to phagocyte activation and results in enhanced antigen uptake/degradation; IgM activates complement very efficiently and can be recognised by C3br; binding of antigen/antibody complexes by C3br present on RBCs delivers the complexes to the liver/spleen for removal by macrophages
adcc is antibody dependent cell-mediated cytotoxicity; NK cells, neutrophils, eosinophils, and phagocytes express FcgRIII, and ligation of this receptor on NK cells triggers release of cytoplasmic granules containing lytic enzymes; ADCC cannot be triggered by free Ig, but requires complexes of antibody/antigen to provide multiple Fc regions for recognition; eosinophils mediate unique form of ADCC to defend against helminths with IgE binding to surface of worms and recognised by FceRI, a high affinity receptor for IgE; the eosinophils then release granules containing proteins that are toxic to helminths, this is esp important as parasites may be too big for phagocytes to ingest
mast cell/basophil Ig receptors and response (and humoral response reg)
Mast cells/basophils have FceRI, binding IgE very strongly, with cross-linking of these receptors when antigen binds signalling for release of inflam mediators into surrounding tissues; the degranulation occurs in seconds and is associated with synthesis/release of lipid and cytokines, prostaglandins, leukotrienes and TNFa; this response is also triggered by allergic reactions when allergens bind to IgE on mast cells; FceRI has prebound IgE for binding of the target antigens
antibody responses shut down by B cells using negative feedback: antibody produced in response to antigen binds and forms immune complexes, B cells specific for the antigen can bind the complexes with FcgRIIb (to bind antibody) and BCR (to bind antigen) at same time, providing a negative signal which terminates the B cell response
MHC - where the gene locus is, what MHC are and what their role is (for each class) and how they differ from Ig/TCRs, how many genes for each class and what is meant by polymorphism, how the loci are inherited and expressed (and why this is advantageous)
MHC is large locus on chromosome 6 coding for MHC I/II and many other proteins involved in antigen processing/presentation; class I/II are cell surface glycoproteins whose function is to present peptides to T cells; have similar 3D structure but significant biochem diffs; class I presents intracellular pathogens, II extracellular; specific binding sites for CD4/8 co-receptors
unlike antibodies/TCRs, single MHC can bind broad range of peptides composed of diff aa combos - promiscuous binding specificity
MHC molecules (Human leukocyte antigens HLA) must be able to present peptides from potentially any pathogen to T cells; polygeny refers to expression of multiple independent loci encoding class I/II genes, three class I (HLA-A/B/C) and 3 class II (HLA-DP/DQ/DR) isotypes; polymorphism refers to existence of many alternative forms of same gene within human pop, with MHC genes being most polymorphic known with large numbers of alleles at each locus, sometimes in excess of 3000;
loci are closely linked genetically and in 97% cases inherited as set of alleles (haplotype); allele expression is co-dominant meaning both mat and pat expressed on same cell; due to polymorphism at each locus, in outbred pops it is virtually impossible for 2 individuals to express same combo of MHC alleles, this advantageous as heterozygotes can present more peptides and activate more T cells than homozygotes
MHC peptide presentation and interaction
each MHC molecule binds different characteristic set of peptides with aa at certain positions on peptide conserved because they need to make specific contacts with pockets in the binding groove, these referred to as anchor residues and together they determine peptide-binding motif for that MHC molecule; aa at non-anchor positions are not as strictly constrained and may show considerable variability, accounting for the diverse range of peptides presented by a single MHC molecule
in the absence of infection, MHC molecules are occupied by self-peptides; peptide presentation requires balance in binding stringency as low results in large no of diff peptides binding giving only a small number of any particular peptide-MHC allele combo at cell surface but high stringency gives many copies of same complex at surface but pathogens with small genome may not have a suitable peptide for presentation by host’s MHC molecules; typically cell with 100,000 MHC class I of single allotype presents >1000 diff peptides; roughly 1/1000-1/10000 random peptides are able to bind a particular MHC allele; individual MHC-peptide complexes may be present at 1-5000 molecules per cell with mean of 100; T cells may be activated by a single MHC-peptide complex but may require up to a few thousand
MHC class I antigen processing - present what, how do proteins end up on MHC I, IFNg effect
present endogenous peptides to CD8 cytotoxic T cells
proteins in cytosol continually degraded into peptides, primarily by proteasome, which are then moved into ER by transporter associated with antigen processing TAP; peptides of suitable length/sequence loaded onto partially folded class I molecules in complex process assisted by range of chaperone proteins; fully loaded MHC peptide complexes released from chaperones and pass through golgi, following secretory pathway to cell surface
IFNg changes proteasome in cells it binds to, so it produces peptides which can bind to MHC class I; genetic non functional tap causes MHC class I deficiency giving feeble CD8 response
MHC class II antigen processing pathway
class II molecules pass through ER during biosynthesis, and binding of peptides in ER prevented by a/b chains associating with third invariant chain Ii which blocks peptide binding groove, acts as a folding chaperone and targets class II/Ii complexes into the endocytic pathway; II Ii complexes pass through golgi and sorted into endocytic pathway where Ii is partially removed leaving a small protein called CLIP in the peptide binding groove; antigens are taken into cell by endocytosis and degraded into peptides by proteases; within protein loading MIIC compartments, CLIP peptide is removed and antigen derived peptides with appropriate binding motifs are loaded into empty class II molecules; MHC class II/peptide complexes are then transported to cell surface for presentation to CD4 T cells; hep C mount CD8 response but this needs macros/DCs to present antigens on MHC I but hep C only infects hepatocytes so phagocytose, present on MHC II, cross presentation to get it onto MHC I - maybe transfer from dead cell to macro in phagocytosis, maybe from endocytic vescile to cytosol allowing usual class I presentation route
T cell subtypes - 2 main types, what each binds and does (4 for first, 4 for second)
specificity controlled by TCR which sees fragmented antigenic peptides bound to MHC molecules; 2 main subsets distinguished by CD4/CD8 expression, effector function and MHC restriction
CD8/TCR bind class I releases cytokines like IFN-g, inhibits viral replication, activates macrophages, kills virus-infected cells and tumour cells; CD4/TCR binds class II, helps naive B cells, activates macrophages, helps CD8 cells and secretes cytokines
T cell selection
selected for: successful beta chain rearrangement, positive selection, negative selection with overall aim to eliminate harmful and reject useless types with only about 1-2% of double positive (CD4+/CD8+) thymocytes surviving selection; negative selection helps prevent autoimmunity by deleting autoreactive cells while positive selection ensures peripheral T cells will be useful since cells that can not recognise self MHC cannot become activated
pos: unique to T cells, newly arranged TCR tested against self-peptide/MHC complexes expressed on cortical epithelial cells in thymus, and those with moderate affinity receive a positive signal to continue maturation with lack of interaction resulting in death by neglect; expression of CD4/8 co-receptors is altered to match MHC restriction - the class to which positive selection took place - with surviving cells being CD4+ single positive if selected against class II complexes or CD8+ single positive if selected against class I complexes
neg: potentially autoreactive thymocytes expressing TCRs with high affinity for MHC/self peptide are eliminated by apoptosis, and negative selection cannot eliminate T cells with receptors recognising combos not expressed in thymus, these instead dealt with by peripheral mechanisms; thus low affinity die by neglect and high affinity negatively selected, so only those with moderate selectivity survive
T cell activation
mature naive T cells have TCRs which recognise MHC/peptide complexes but require additional stim to activate with 2 signal hypothesis proposing that signal 1 is TCR engagement with MHC and co-stim molecules giving signal 2 eg CD28 interacts with B7.1(CD80) and B7.2(CD86) on the APC and CD40L on T cell interacts with CD40 on APC; both sets of molecules deliver essential signals to T cells without which they don’t become activated; expression of co-stim molecules is defining feature of pAPCs; some CD8 need DC and activated CD4 for same virus (make IL2) in order to be activated
