Clinical Immunology (16-27) Flashcards
1
Q
How can NK cells subsets be identified?
A
identified by expression levels of CD56
- CD56 bright are cytokine producing
- CD56 dim are cytotoxic
- a third subset lacking CD56 has recently been discovered
2
Q
How do NK cells deal with infection?
A
- killing via perforin/granzyme system
–> important for antiviral and antitumour response - produce cytokines such as IFN-gamma to modulate immune responses
3
Q
How are NK cells activated?
A
- NK cells are constantly exposed to activation and inhibition signals
- binding to self MHC inhibits them from being activated
- When self MHC is missing, NK cells usually enter an activated state and release immune mediators or cytotoxic granules to kill their target
4
Q
Is missing self MHC alone enough to induce activation?
A
no, as all blood cells would be lysed
lacking MHC does not activate an NK cell, it simply reduces the activation threshold needed to activate them
other stress molecules such as cytokines activate NK cell
5
Q
When would cells be missing MHC class I?
A
- certain viruses can downregulate MHC class I to prevent antigen presentation
- tumour cells reach equilibrium where their formation rate is the same as their rate of removal by the immune system
- once tumour cells downregulate MHC class I, it allows the tumour to escape the immune response and become malignant
6
Q
How do NK cells synergise w the T cell response?
A
NK cells are able to target infected cells that the T cell would not be able to recognise
NK cells can be activated much easier than CD8 T cells
- do not require antigen presentation in order to activate
7
Q
How do NK cells mediate antibody dependent cellular toxicity?
A
The Fc receptor, FC-gamma-RIII (CD16) on NK cells recognise antibodies bound to target antigen
crosslinking causes NK cell to release intracellular stores of perforin and granzymes
perforin punctures holes in cell membrane allowing granzyme to enter target cells and induce apoptosis
8
Q
What are primary immunodeficiencies (PID)?
A
genetic immune deficiencies
disorders in which part of the immune system is either eliminated or functioning abnormally
leads to increased heightened susceptibility to infection by particular classes of pathogens
different to AID (AIDS), which is a result of external infection or disease treatment
9
Q
What are some genetic characteristics of PIDs?
A
most single gene PIDs are recessive
ie one good gene compensates for a faulty one, more common if parent are genetically related
majority of PIDs are X-linked recessive
- where generally only males show symptoms eg IPEX, X-linked SCID
- X inactivation would preferentially inactivate chromosome with the mutation in the sense that cells that carry the good chromosome are allowed to progress
often complete loss not compatible with life, so mutation may produce gene product w partial function-hypomorphic
10
Q
How can susceptibility to certain types of pathogens give a clue to type of PID?
A
CD4 T cells enhance innate immune responses and types of opportunist infections can gve a clue to type of PID since different types specialise against different ones
eg increased susceptibility to extracellular bacteria may mean a deficiency in Th17
11
Q
What opportunistic infections correlate with what immune cell deficiencies?
A
- intracellular bacteria
- macrophage or T cell defect - extracellular encapsulated bacteria
- defect in antibody, complement, phagocytes or Th17 - fungal
- T cell dysfunction - recurrent herpes viruses
- NK and CTL deficiency
- viral susceptibility might lead to cancer
12
Q
When to think of PID as a diagnosis?
A
- recurrent infections
- opportunistic pathogens
- normally mild infection becomes life threatening
- persistent high WBC counts
- persistent low WBC counts
13
Q
If PID is suspected, as an immunologist what would be the next steps?
A
- haemoglobin levels
- total and differential WBC count
- platelet count
- analysis of lymphocyte subsets for numbers of T, B, and NK cells
- microbiology on organisms isolated
- check antibodies made to commonly used vaccinations
- request tests for severe combined immunodeficiency (SCID)
–> infants w SCID have undetectable or v low levels of T cell receptor excision circles
–> if VDJ recombination does not happen = not T cells as this is required for maturation
14
Q
How can B cell function be evaluated in an individual in vitro?
A
induced antibody production in response to pokeweed mitogen
15
Q
How can T cell function be evaluated in an individual in vitro?
A
proliferation in response to phytohemagglutinin or to tetanus toxoid
16
Q
How can phagocyte function be evaluated in an individual in vitro?
A
phagocytosis of colourless nitroblue tetrazolium will turn phagocyte blue due to release of ROS
if this does not occur then their is a deficiency in the ability of the phagocyte to kill pathogens
used to test for chronic granulomatous disease
17
Q
What are the treatment options for those with PIDs?
A
- treat symptoms
PIDs need antimicrobial therapy to clear and prevent infection - replace what is missing
a) antibody replacement therapy
eg Intravenous Immunoglobulin (IVIG)
IgG antibodies to many different pathogens administered evert 3-4 weeks
after that IgG could be given subcutaneously by self administration
b) complement similarly replace using donor material
18
Q
What are long term treatments for PID?
A
a) replace
stem cell therapy and/or gene therapy
b) activate
phagocytes can be activated w injections of IFN-gamma
c) stimulate proliferation
if neutrophils not produced in normal numbers, granulocyte colony-stimulating factor (G-CSF) raises levels of white cells including granulocytes
19
Q
What is the most common type of SCID and how can it be cured?
A
a mutation in the common gamma chain (CD132) on T cells prevents IL-2 signalling, inhibiting T cell proliferation
activation of B cells does not happen as there are not T cells to induce isotype switching
–> can only produce IgM
–> looking at levels of antibodies is important
can be cured w a bone marrow transplant
results are less satisfactory if the patient has active infections at the time
20
Q
In what situation is gene therapy used to treat PIDs?
A
allowed only if
- no bone marrow match is available OR the patient is too ill to have transplant
AND
- patient has life-threatening infection unresponsive to conventional treatment, including steroid
21
Q
What is agammaglobulinaemia?
A
a type of PID that results in no Igs
due to Bruton tyrosine kinase (BTK) mutation
–> crucial role in B cell development
stop codon found by gene sequencing due to deletion of 4 bps
–> frame shift
–> no mature B lymphocytes
associated w failure of Ig heavy gene rearrangement
22
Q
What is the role of BTK in B cell maturation?
A
signalling insufficient without BTK to induce differentiation into mature peripheral B cells
- BTK overexpression in B cells get uncontrolled Ab production and systemic lupus erythmatosus (SLE)-like disease
–> effective BTK inhibitor is ibrutinib
23
Q
What is chronic granulomatous disease (CDG)
A
phagocytes require NADPH oxidase (PHOX) to digest bacteria they have taken up
–> respiratory burst is critical for killing bacteria
defects in any one of four essential subunits of PHOX can cause CDG of varying severity
formation of granulomas due to phagocytes not being able to kill pathogens they have taken up
24
Q
How can CDG be treated?
A
- continuous antibiotic therapy to help prevent antibacterial infections
–> infections usually require additional antibiotics - corticosteroid drugs for treating granulomatous complications
- IFN gamma
- bone marrow transplants have proven to be successful in some cases
25
If you have a case study where listeria is present what area of the immune system should you suspect?
complement
26
What is Type I hypersensitivity?
IgE- mediated
immediate
27
How are IgE's produced and how do they induce an immune response?
Th2 cells produce IL-4 which induces B cell class switching to IgE
v low level in serum
bound to Fc-epsilon-1 receptors on mast cells
- antigen crosslinking induces degranulation
--> v few IgE molecules needed
- usually antibodies can only bind receptor if it has antigen bound, IgE is an exception
28
What are the two different types of granules in a mast cell?
1. preformed granules
immediate release
2. synthesised after activation
delayed release
29
What molecules are contained in a mast cell?
Cytokines
- IL-3 signals eosinophils to arrive at site and IL-5 promotes degranulation, releasing major basic protein
- IL-4 activates Th2 cells, and more IgE production
- proteolytic enzymes activate components of complement
- histamine promotes smooth muscle contraction in the gut
30
What is the result of intravenous entry of allergen?
IgE mast cells receive systemic delivery of antigen resulting in widespread release of histamine which acts on blood vessels to increase permeability
- leads to hives at low doses (>mg)
- in higher amounts, can lead to anaphylactic shock (mg-g)
31
What is the result of subcutaneous entry of allergen?
causes wheal and flare reaction in skin
wheal: local inflammation
flare: redness around wheal due to vasodilation
32
What is the result of entry of allergen through inhalation?
nhalation causing exposure in upper respiratory tract leads to increased mucous production and nasal irritation
asthma in the lower respiratory tract causes contraction of bronchial smooth muscle
where the allergen gets into the airway is dependent on the size of it as well as the concentration
33
What is the result of entry of allergen through ingestion?
ingestion causes contraction of intestinal smooth muscle, causing vomiting
flow of fluid into the gut causes diarrhoea
- anaphylaxis
34
What is anaphylactic shock?
induced by food: 5-120 minutes
skin eg insect bite: 5-30 minutes
serious allergic reactions such as narrowing of airways, vomiting, sudden blood pressure drop
needs urgent treatment
35
What are the risk genes?
- genes associated with increasing Th2 or Th17 responses
- FceR polymorphisms
- reduced skin barrier function
it is the RISK of allergy that is inherited, not the specific allergy
36
How can allergens be determined?
testing can be done by a skin prick test, where potential allergens are put underneath the skin
37
How can allergy be treated?
1. avoidance
2. antihistamines
--> blocks specific histamine receptors
3. beta2-andrenergic agonists
--> preventing smooth bronchial muscle contraction in asthma
4. epinephrine (adrenaline)
stimulates both alpha and beta adrenergic receptors, decreases vascular permeability, so increases blood pressure, and reverses airway obstruction
--> epipen
38
What are two strategies for allergen immunotherapy and desensitasation?
1. inducing Treg production by increasing dose of antigen through subcutaneous injection
- secrete IL-10
- reduces Th2 activity
- reduces IL-4
- reduces IgE secretion
- specific IgG secretion increases
2. allergenic dose of allergen delivered orally as mouth contains few mast cells
- no allergy symptoms
- induce Tregs
- secrete IL-10
- reduces Th2 activity
- reduces IL-4
- reduces IgE secretion
- specific IgG secretion increases
- eventually leads to reduced allergy symptoms, even when exposed to allergen eg pollen in nose
39
What is Type II hypersensitivity?
other antibody types binding to cell surface antigens
often RBCs
--> immune-mediated haemolysis by activation of complement and/or antibodies opsonize cell
eg penicillin allergy
--> binds to RBC surface, if antibodies react to penicillin they will bind and induce macrophage uptake
40
What is Type III hypersensitivity?
Immune complex (IC) mediated
--> lattices of antigen and antibody
consequence of IgG binding antigen to form an immune complex
eg farmers lung, antibodies against mould spores cause inflammation in the lungs
41
What is Type IV hypersensitivity?
a delayed response, mediated by T cells
--> cellular hypersensitivity
eg T1 diabetes: T cells destroying beta cells in pancreas which produce insulin
42
What is Type V hypersensitivity?
antibody mediated that are specific for cell surface receptors like type II
--> the difference is the response is stimulatory instead of destructive
eg Grave's disease
43
What is Graves' disease?
Type V hypersensitivity
overactive production of thyroxin
--> antibodies stimulate TSH receptor without presence of hormone, which leads to production of thyroid hormones, but the negative feedback loop does not work as autoantibodies are still being made
--> heat intolerance
--> anxiety
--> bulging eyes
44
Why was there a delay in tumour immunotherapy?
due to genetic origins, the immune system was thought not to be involved
45
What was the experiment that first showed that cancer is an immunological disease as well as a genetic one?
both immunodeficient and immunocompetent mice where injected with carcinogens
after 200 days, it was seen that there was a higher percentage of immunodeficient mice with tumours compared to immunocompetent
46
How can tumour immunoediting result in malignant tumours?
- cancer cells downregulate MHC-I
- changing antigens to avoid T cell response
- upregulating non-specific antigen onto MHC to avoid immune response
- can recruit immune cells such as Tregs and M2 macrophages that secrete TGF-beta and IL-10 to dampen immune response
--> macrophage can promote angiogenesis
47
How can monoclonal antibodies be used to target the tumour directly?
block growth factor receptors
eg trastuzumab, binds to HER2
--> improves median survival in breast cancer patients
--> This blockade inhibits HER2-mediated signaling cascades that promote cell proliferation, survival, and angiogenesis
eg rituximba binds CD20, blocking B cell activation
--> treats rheumatoid arthritis and B cell lymphoma
deplete tumour cells expressing tumour associated antignens
eg CD38
48
How can monoclonal antibodies be used to target the tumour immune response?
block checkpoint inhibitors
eg CTLA-4
BiTEs used to enhance T cell function
49
How does mAb binding kill tumour cells?
1. direct killing
binding of mAb causes downstream signalling = apoptosis
2. complement-dependent cytotoxicity (CDC)
- C1q binds Fc = lysis of cell
3. Antibody Dependent Cellular Cytotoxicity (ADCC)
FcyRIII of NK binds Fc on mAb, releasing perforin/granzyme
3. antibody-dependent phagocytosis (ADP)
macrophage FcyR binds mAb intiating phagocytosis
50
What is a cold tumour?
send inhibitory signals that can downplay T cell response, as well as remove B7 from DCs
cancer cells will release anti-inflammatory signals that will cause T cells to upregulate CTLA-4 expression
also upregulate PD-L1 on their own cells which bind PD-1 on T cell, again downregulating them
- generation of antibodies against these will stop this downregulation of T cell activity
exclusion of CD8+ and NK cells from tumour
51
What is a hot tumour?
CD8+ T cells and NK cells are present in tumour
suppression of immunosuppressive cell types
improved prognosis and killing of tumour cells w immunotherapy treatment
PD-1 or CTLA-4 blockades have an effect as T cells are present
52
What are Bispecific T cell engagers (BiTEs)?
fusion proteins consisting of two single chain avriable fragments (scFv) derived from different antibodies
one of the scFvs binds to T cells via the CD3 receptor, and the other to a tumour cell via a tumour specific molecule
this draws T cell and the tumour cell closer together and induces T cell signalling via CD3
other designs include antibody structures to also draw in cells via Fc receptors to help w antigen presentation and phagocytosis
53
What is autologous T cell therapy?
individuals naturally produce an anti-tumour response including generation of anti-tumour T cells
--> some will be better at controlling the tumour than others
--> take T cells and culture them w tumour cells and see which are responding to them
--> expand them and put them back into patient in combination w anti-PD1 or anti CTLA-4
54
How can autologous T cell therapy be improved?
identification of tumour specific antigens (new or overexpressed)
1. vaccinate against antigens
2. engineer T cells that respond to antigen (again in combo w anti-PD1 or anti-CTLA-4)
55
What is a chimeric antigen receptor T cell (CAR-T)?
- Fab region of an antibody
- signalling molecule such as CD28
--> as T cells do not have signalling molecule
this bypasses need for co-stimulation
- can be generated from the patient's own T cells creating an autologous T cell therapy
- kill switches can be built in to aid in the removal of the CAR T cells once the cancer has been cleared
56
What are CAR NK cells?
similar to CAR-T cells
push them to overcome MHC class I signalling that suppresses them
57
How can chemokines be used in cancer therapy?
CCL2/CCR2 axis is important for tumourigenesis
CCL2 upregulated early in tumour development
--> allows tumours to recruit macrophages to help promote tumour growth and immune suppression
ACKR2 scavenges and removes excess CCL2
58
Why is CCR2 important for NK cells for controlling tumours?
needed for migration to tumours to perform cytotoxic functions
59
How can DCs be improved in the tumour response?
inject DCs that have been preloaded w antigen
take cells from bone marrow and culture them w specific signals to induce DC differentiation
only some will express CCR7:
- receptor necessary to migrate to lymph node
- increase in MHC expression
- increase in costimulatory molecule expression
sorting DCs for CCR7 improves their efficacy as a tumour therapy
60
What are two major challenges facing transplantation?
- shortage of organs
- loss of organs due to immune injury
testing of donor and patient needs to be done to match them as closely as possible
--> liver does not as it has high regenerative ability
61
What is ischemia and reperfusion injury (IRI)
a complex pathophysiological phenomenon, inevitable in kidney transplantation and one of the most important mechanisms for non- or delayed function immediately after transplantation
due to organ being outside of the body, some damage is unavoidable
reduced oxygen within tissue
- ednothelial cell damage
- immune cell activation
- chemokine and cytokine release
- more immune cell recruitment
62
What is the allo-immune response?
response against foreign tissue
soluble arm:
- complement activation is a major contributor to IRI
- via alternative and MBL activation pathways
cellular arm:
- neutrophils, macrophages, NK cells
63
What is the cause of foreign tissue rejection?
Human Leukocyte Antigens (HLA)
set of polymorphic molecules on the surface of human white cells
the HLA complex is a set of genes that encode for MHC molecules
- class I, II, and III
at each HLA class I gene locus (A,B, and C) an individual can have 2 alleles
- therefore a max of 6 different class I molecules at the cell surface
for class II, an individual can have max 4 different DR antigens at the cell surface, 4 DQ antigens, 4 DP antigens
- therefore, a max of 12 class II molecules at the cell surface
64
What are the consequences of exposure to foreign HLA?
- T cell activation
--> in transplant setting leads to graft rejection and Graft v Host Disease (GvHD) in haematopoietic stem cell transplantation (HSCT)
--> allorecognition by 3 routes; direct, indirect, and semi-direct
- anti-HLA antibodies may also be produced by exposure to foreign HLA
--> pregnancy
--> transplantation
--> blood transfusion
65
What are the 3 routes of allo-recognition?
direct
--> APC from donor w non-self HLA can be directly recognised by recipient T cells
--> due to leakage from process in thymus where self-recognising T cells are removed
indirect
--> foreign
HLA comes off of donor cell, picked up by APC and presented to T cells
--> like normal immune response
semi-direct
--> HLA antigen is not processed and by some method is presented on an APC
--> "like magic" - lecturer
66
What percentage of the T cell pool activates against foreign tissue?
1-10%
67
What are neoantigens?
antigens generated by tumour cells because of genomic mutations
Neoantigens often represent foreign or altered protein sequences that are not recognized as self by the immune system
can be taken up by B cells which present this to a Th which activates B cell and creates antibodies
also promotes anti-tumour CD8 responses
68
How can anti-HLA antibodies be identified?
semi-quantitative assays such as Luminex
allow us to identify which HLA antibodies are present in a patient's serum and their level
HLA antibodies can cause problems in transplantation
69
What are two broad ways of managing immune responses in transplantation?
1. immunosuppressive drugs
--> given at time of transplant and for lifetime of the graft
2. matching donor and recipient
--> try to reduce how 'foreign' the donor looks to the recipient immune response
70
How is an organ donor's HLA type categorised?
- PCR based methods
- most labs have introduced next generation sequencing (NGS)
71
How likely is a complete HLA match?
rare
HLA-A, B, DR are most important to match
nowadays the immunosuppression methods are better so mismatches are less likely to reject, but still worth typing
72
In what contexts are HLA antibodies relevant?
- as pre-formed donor specific antibodies, present at the time of transplant (females after pregnancy, patients after previous transplant
- as de novo antibodies that develop as a result of HLA mismatched transplant
73
What is the procedure for HLA antibody testing (Luminex)?
- 100 different colour coded polystyrene beads in a single tube
- each bead population coated with selected class I or class II antigens or pool of antigens for screening
1. microbeads coated w HLA antigen incubated w patient serum
2. wash beads
3. incubate w PE conjugates w anti-human IgG
4. wash beads
5. run beads on Luminex - assign assay reactivity and antibody specificities
74
What are the types and causes of rejection?
hyperacute
--> minutes - hours
--> high levels of preformed anti-donor ABO or HLA antibodies and complement
accelerated
--> days
--> reactivation of sensitised T cells/low level of preformed HLA antibodies
acute
--> week/months
--> primary activation of T cells
chronic
--> months
--> de novo HLA antibodies, immune complexes, slow cellular reaction, recurrence of disease
75
What are two ways of crossmatching donor and recipients HLA types?
wet XM: flow cytometry
virtual XM: use donor HLA typing data and patient Luminex HLA antibody data to predict likelihood of a positive XM
76
What is the interesting thing about haematopoietic stem cell transplant (HSCT)?
the donor immune system can recognise recipient as foreign
--> other way round
need as close an HLA type match as possible to reduce risk of GvHD
77
What are the stages of HIV infection?
Acute Primary Infection Syndrome
--> flu-like illness, w high levels of virus replication
--> appearance of anti-HIV CTLs
--> infection is brought under immune control
Asymptomatic infection
--> no outward sign of disease, although there is a slow decline in the CD4 count and v active viral replication
--> this stage can persist for 10+ years
Symptomatic HIV infection and AIDS
--> the immune system ceases to function and disease progresses, resulting in death
78
What are some diseases associated with HIV-1 infection?
- TB is most frequent cause of death in HIV-1 infection
- usually asymptomatic herpesviruses are now symptomatic
- Candida spp. and cryptococcus
- toxoplasmosis
79
How can HIV be diagnosed?
1. screening test (ELISA)
--> high sensitivity
THEN
2. confirmational test (Western Blot)
--> high specificity
THEN
3. course of therapy (quantitative PCR)
80
What are the steps of an indirect ELISA?
1. coating the surface of a microplate well with antigen
2. blocking unbound sites with a blocking buffer to prevent non-specific binding
3. incubation w serum
4. wash to remove any unbound substances
5. incubation w secondary antibody conjugated with a detection enzyme eg horseradish peroxidase
6. washing
7. incubation of substrate causing a reaction with any enzyme present causing a colour change in substrate which can be quantified
81
What is a HIV-1 point of care test (POCT)?
like COVID-19 tests
add sample of whole blood and add chase buffer
detects HIV-1 p24 antigen and HIV-1 antibodies
82
What is HAART?
Highly active anti-retroviral therapy
a combination of many drugs that target different aspects of the HIV-1 virion
- entry inhibitors
- nucleosidic reverse transcriptase inhibitors (NRTIs)
- non-nucleosidic revers transcriptase inhibitors (NNRTIs)
- integrase inhibitors
- protease inhibitors
83
How is HIV-1 diagnosed from a Western Blot?
negative
--> no bands
--> wrong bands
equivocal
--> one or two bands
--> Gag, Pol, or Env
positive
--> at least one band each
--> Gag + Pol + Env
84
What is the concept of One Health?
improving animal health improves human health and vice versa
85
What percentage of all human pathogens are zoonotic?
60%
75% of emerging infectious diseases affecting humans are animal origin
86
Who was the guy that developed the smallpox vaccine?
Edward Jenner in 1796
exposed some boy to cowpox and then infected him with small pox
--> no infection
smallpox eradicated in 1980
87
What was wrong with the "MMR Vaccine and Autism" study published in 1998?
was discredited due to ways experiments were conducted and how results were interpreted
MMR vaccine given before 1 years old, when autism arises
correlation does not equal causation
because of this there was a huge decrease in numbers of people letting their children have the MMR vaccine
--> 2019 has the highest number of measles deaths globally for 23 years
88
What are the pros can cons of live attenuated vaccines, such as the smallpox and measles vaccines?
benefits: induces strong, protective immunity
risks: potential reversion to virulence and/or may not be suitable for immunocompromised individuals
89
What is the target product profile (TPP)?
what is the vaccine aiming to do?
how will it be deployed?
what is target population?
the TPP combine scientific and practical elements
needs to be defined early in vaccine development
primary criteria: safety and efficacy
90
What are the pros and cons of killed/subunit vaccines?
pros: tend to be safer
cons: require adjuvants for efficacy, often require multiple doses and poorer at inducing cellular maturity
91
What are vaccine platform technologies?
generic technologies that can be applied to vaccine development for different infections/diseases
eg
- nanoparticles that incorporate recombinant protein antigens
- vectors that encode antigens of interest
--> antigens from different pathogens can be used, not just viral
--> induces MHCI-CD8 presentation, big barrier for subunit vaccines
- nucleic acid vaccine
--> self-amplifying RNA (saRNA) vaccines offer a low-does alternaitve
--> cheaper
--> not approved for use in humans
best type to use is dependent on the TPP
92
How was the SARS-CoV-2 vaccine developed so quickly?
took 300 days from identification to approval of vaccine
prior knowledge of coronavirus biology, immunology, epidemic preparedness and vaccine platform technologies facilitated the rapid response
93
What is the differences between the different SARS-CoV-2 vaccines?
each platform delivers the same antigen in different ways
--> Wuhan S protein
- mRNA vaccines induces higher antibody levels than those found in convalescent sera
- AdV (Alum-CpG-adjuvated/inactivated) induce cellular responses after primary injection and are better for CD8+ induction
Th1 bias associated w better outcomes
94
What is the clonal selection theory?
lymphocytes express receptors of a single antigenic specificity
--> this specificity is genetically determined and precedes antigen encounter
antigen only stimulates cells w specific receptors and induces clonal expansion of that lymphocyte population
this theory has underpinned the formulation of paradigms that explain immunological self tolerance and immunological memory
95
Why does each lymphocyte only express receptors of a single antigenic specificity?
this is because if there is a second receptor on the lymphocyte that recognises a self antigen, that lymphocyte will be destroyed which means losing the potentially crucial non-self recognising receptor
96
What were the 3 concepts that Pete Medawar proposed to explain why women fail to reject a semi-allogenic foetus?
1. the placenta is a barrier between the mother's immune system and the foetus
2. the foetus does not express the paternal molecules that would be recognised by the maternal immune system
3. the maternal immune system is suppressed
there are varying degrees of truth in all of these but none singularly apply
in its simplest form the clonal selection theory cannot explain mammalian pregnancy
97
What is the type of placenta in humans?
haemochorial
maternal tissue layers all removed, foetal chorion bathed in maternal blood
human placentation is therefore the greatest challenge to the concept of the placenta being a physical barrier to the immune system
- anti RhD antibodies
- syncytiotrophoblasts (epithelial cells) express the neonatal Fc receptor (FcRn) which binds IgG and facilitates antibody transfer across the placenta (passive protection)
but no direct mixing of blood
98
What is the function of the placenta?
despite structural differences between species, function is conserved: to provide nutrients to the foetus and remove waste metabolites
99
What is extravillous trophoblast (EVT) invasion?
invasion of these cells into the decidua is important for opening up the spiral arteries
they are bathed in maternal blood
mediated by certain uNK cells
100
Why does paternal MHC expression not cause foetal rejection?
EVTs express HLA-C, a classical polymorphic locus
HLA-C2 is much rarer than HLA-C1, and is therefore a discriminator
C2 can bind A and B haplotypes
a KIR AA homozygous mother and C2C2 foetus is an inhibitory combination resulting in failure to activate uNK cells
KIR AB heterozygosity or KIR BB homozygosity results in activatory signals
KIR-HLA interactions determine determine uNK activation and function and can therby influence pregnancy outcome
101
What NK cells are present in the pregnant uterus?
uNK cells
CD56 bright, CD16-
as opposed to CD56 dim, CD16+ NK cells that predominate in peripheral blood
activated uNK cells produce factors that are important for remodelling of spiral arteries (VEGF) and trophoblast invasion (GM-CSF)
102
What are Killer Ig-like Receptors (KIRs)?
activatory and inhibitory receptors
nomenclature is based on the number of extracellular Ig-domains eg 2D, and length of the cytoplasmic tail (L, long; S, short)
L domains have immunoreceptor tyrosine-based inhibitory motifs (ITIMs)
S domains have immunoreceptor tyrosine-based activation motifs (ITAMs)
two haplotypes
- A haplotype tends to be inhibitory (more inhibitory genes)
- B haplotype tends to be activatory (more activatory genes)
103
What are the 3 major subpopulations of uNK cells?
High, medium, and low KIR expression (1,2,3)
Low, medium, and high IFN-gamma production (1,2,3)
--> IFN-gamma production is regarded as incompatible w successful pregnancy
uNK1 are most likely responsible for regulating placentation due to their localisation, characteristics, and interactions w EVTs
uNK3 are most likely involved in immune defence
104
How do local mechanisms in the placenta shape the anti-inflammatory environment?
expression of regulatory cytokines predominates (IL-10, TGF-beta)
tryptophan degradation by foetal trophoblast IDO can tolerise maternal CD8+ T cells to paternal antigens
105
Why is it clear that a pregnancy does not result in immunosuppression?
generalised immunosuppression would put the other at risk of infection and disease, this would be disadvantageous for the foetus
however there is evidence that the maternal immune system is modulated during pregnancy
106
How are autoimmune diseases evidence of immune modulation during pregnancy?
- Rheumatoid arthritis (RA) and multiple sclerosis (MS) tend to go into remission during pregnancy
--> associated w Th1/proinflammatory cytokines (IFN-gamma)
- systemic lupus erythmatosus (SLE) tends to flare up
--> associated w Th2/anti-inflammatory cytokines (IL-4,5,13)
oestrogens and progesterone both inhibit Th1 and Th17 responses, while promoting production of Th2 responses
--> RA/MS remission and SLE progression during pregnancy
strong evidence for subtle maternal immune modulation via cytokine production
107
In medical diagnostics, what is test sensitivity and specificity?
test sensitivity: the ability of a test to correctly identify those with the condition/disease (true +ve rate)
--> sensitivity = true positives/true positives + false negatives
test specificity: the ability of the test to correctly identify those without the condition/disease (true -ve rate)
--> specificity = true negatives/true negatives + false positives
108
What 2 conditions does a test require?
1. standard operating procedures: how to carry out a test in a consistent matter
2. controls: need to know if the tests has been carried out correctly and if a positive test could have been achieved
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What are 2 types of sample collection?
1. non-invasive: use of wats products for detection of symptoms
--> urine: compounds, sugar levels
--> faecal matter: blood
--> exhaled breath: alcohol levels, lung capacity, respiratory biomarkers
--> saliva: HepB, HepC, HIV etc
--> microbial cloud; telling of person's environment, may be a diagnostic in the future
2. invasive sample collection: checking of sites to test for infection
--> back of throat
--> nose
--> blood prodcucts
110
What is baseline information?
baseline information from a healthy population/individual, allows us to determine atypical readings or change
111
What are the pros and cons of direct observation?
pro: provides tangible evidence
cons: diagnosis is not binary, if you don't see is, that doesn't mean it's not there
- accuracy of diagnosis is determined by the skill of the microscopist
112
What are the pros and cons of indirect observation?
can utilise several areas of the immune system
- serology
- cytokines
- IFN Gamma Releasing Assays (IGRAs)
- Skin tests (TB, leprosy, allergic reaction)
when using Ig's, they need to be 100% reliable due to how specific they are
- if they are not the whole tests falls apart
113
Why are antibodies utilised in diagnosis?
1. a patients antibodies will provide info on the history of exposure
2. we can use commercially produced antibodies to detect for the presence of an antigen within a patients blood
114
How can diagnosis using indirect ELISA be improved?
using a computer to quantify colour change instead of human opinion
0.9 to 1.1 = borderline: retest to confirm
it may be necessary to perform the test on repeat samples taken from the same host at some time interval (eg 14 days) to document a rising titre of antibodies to that specific antigen (active infection)
115
What considerations need to be taken into account when testing?
1. false positive
2. false negative
mainly due to:
- non-specific binding or cross recognition
- delay in the immune response
116
What are the benefits of a rapid diagnostic tests?
- cheap
- quick
- reliable
- easy to use and interpret
- stable under extreme conditions
- done at home = less risk of spreading disease
currently targeted at:
- HIV
- HepB
- malaria
- syphilis
- trypanosomiasis
- COVID-19
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What is the mechanism of action of the COVID-19 lateral flow tests?
1. material from nasopharynx dropped onto sample pad, which is pulled through by capillary action
2. buffer contains antibodies against SARS-CoV-2 which bind antigen in material
3. Test antibodies bind to antigen
4. control antibodies bind to antibodies in buffer
malaria test works similarly, except blood is used and it can distinguish between the two main causal parasites
--> adaptable to parasite evolution eg response to HRP-2 deletions
118
What is rheumatoid disease?
any disease marked by inflammation and pain in the joints, muscles, or fibrous tissue, especially rheumatoid arthritis
- skin
- blood vessels
- nerves
- muscles
- bones/joints
- internal organs eg heart/lungs
- gut
rheumatoid arthritis is so common becuase we use our hands so much cauing microcuts which can lead to eventual overexpression of IL-17 and Th1 responses
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What is vasculitis?
blood vessel inflammation
different diseases affect different blood vessels
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What is large vessel vasculitis?
blocking of blood vessels supplying the optic nerve by immune cells
swelling of vessels on side of head
eventual loss of site
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Why must rheumatoid arthritis be treated ASAP?
treated aggressively as it can irreversibly stretch the tendons
- deplete B cells: rituximab
- interfere w cytokine function: anti-TNF-alpha, anti-IL-6
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How does dysregulation of Th17 lead to rheumatic disease?
- excessive production of interleukin-17 (IL-17) contributes to chronic inflammation and autoimmune responses in rheumatic diseases like rheumatoid arthritis (RA) and psoriatic arthritis
- Th17-derived IL-17 promotes tissue damage by recruiting immune cells, stimulating autoantibody production, and disrupting the balance with regulatory T cells
- Imbalances between Th17 cells and regulatory T cells exacerbate inflammation and autoimmune pathology in rheumatic diseases, highlighting Th17 cells and IL-17 as potential therapeutic targets
