Immunology Flashcards
What type of virus is HIV
RNA retrovirus single stranded
Belongs to lentivirus family
Which cells do HIV infect
CD4+
- t helper cells
- macrophages
Pathogenesis of HIV
Attaches to CD4 via GP120 but uses co receptor either CCR5 or CXCR4
Replicates via a DNA intermediate
Integrates into host genome
HIV DNA transcribed to viral mRNA
Viral RNA translated to viral proteins
Packaging and release of mature virus
What can predict HIV disease progression
Initial viral burden after primary infection settles
What CD4 count defines AIDS
Less than 200
Response when recognise PAMP
Th1 and h17
How does immune system respond to toxins and helminthes
Detect a loss of function then get Th2 response
What are inborn errors of immunity
Heterogenous group of genetic disorders resulting in immune dysfunction and ill health
485 single defects already identified
What is the most common form of inborn errors of immunity
Antibody deficiency or B cell function
What gene defects result in suceptibility to mycobacterial and BCG infection
Gene defects in generation of IL-12 adn response to IFN-gamma
Leads to reduced production of TNF to activate oxidative pathways
What gives rise in critical influenza pneumonia susceptibility
Defects in TLR3 which is sensor of influenza A
What is in mucous from membranes which protects against microorganisms
IgA prevents bacteria and viruses from binding to epithelial cells
Lysozyme which breaks down cell walls
Lactoferrin which starves bacteria of iron
Which cells form part of innate immune response
Polymorphonuclear cells
Dendritic cells
Monocytes and macrophages
NK cells
Where are granulocytes produced
Bone marrow then migrate to site of injury
Other than cells what is included in the innate immune system
Complement
Acute phase proteins
Cytokins and chemokins
What are examples of pattern recognition receptors
TLR
RIG-1
What are monocytes and macrophages
Monocytes are produced by bone marrow and migrate to tissues where differentiate into macrophages
Function of macrophages
Phagocytosis
Present processed antigens to T-cells
What are mannose receptors
C-type lectin receptor found innate cells which detects pattern
What type of receptors are those detecting PAMPs
Fc receptors
What is opsonisation
Enables phagocytosis by marking the pathogen and making a bridge between it and phagocyte receptor
What are examples opsonins
Antibodies
Complement components
Acute phase proteins
What are 2 types of microbial killing
Non-oxidative- release bacteriocidal enzymes into phagolyosome
Oxidative- produce hydrochlorous acid
What forms pus
Phagocytosis depletes neutrophil glycogen store which results in cell death
As cell dies enzymes are released causing liquefaction of adjacent tissue
What is function of dendritic cells prior to phagocytosis
Found in peripheral tissue
Express Fc receptors for Ig to detect immune complexes
What mediates migration of dendritic cells to lymph node
CCR7
What are the components of the adaptive immune system
Humoral immunity
Cellular immunity
Chemokines and cytokines
What makes up humoral immunity versus cellular
Humoral- B lymphocytes and antibodies
Cellular- T lymphocytes
What are the primary lymphoid organs
Organs where lymphocytes develop
Bone marrow- both T and B haemopatoetic stem cells and where B cells mature
Thymus- where T cells mature
What are the secondary lymphoid organs
Sites where naive lymphocytes and microorganisms interact
Spleen
Lymph nodes
MALT
What do all T cells express
CD3+
When is the thymus most active
Foetal and neonatal stages of life
Involutes after pregnancy
HLA class 1 proteins
A, B, C
HLA class 2 proteins
THINK QPR:
DR, DQ, DP
Most important HLA matches
THINK DR. British Airways (BA)
In order
DR
B
A
When matching donors you want to minimise HLA differences
What does
- isograft
- allograft
- xenograft
- split graft mean
Iso- from a twin
Allo- from same species
Xeno- from different species
Split- shared by 2 recipients (liver)
Complications of Stem Cell Transplant (SCT)
Graft failure
Infections
Graft vs Host Disease (GVHD)
Relapse
What is Graft Vs Host Disease (GVHD)
Where donor cells recognise the patient as foreign
Acute GVHD presentation
Rash which can blister
GI- D&V with bloody diarrhoea
Liver- jaundice
Days to weeks
How is acute GVHD prevented
Methotrexate
Corticosteroids
Cyclosporin
Main prognostic factor for acute GVHD
Previous acute GVHD
What is pathology behind allergic reaction triggering
Normal epithelial function affected- breaking of epithelial barrier
Which route of transmission promtoes IgE sensitisation
Skin
Resp tract
If its oral it promotes IgG immune tolerance
What causes rapid onset symptoms in allergic reactions
Cross linking of IgE on the surface of mast cells and basophils
- release of histamine from granules
- release and synthesis of leukotrienes and prostaglandins
- pro-inflam cytokines which recruits inflam cells
- increases lymphatic flow to regional lymph nodes
- contraction of muscles in lungs and activation of sneezes and itches
What results in delayed symptoms of allergic reactions
Eosinophlic related tissue damage and cytokine release from Th2 T-cells (IL4, IL5, IL13)
What is most appropriate initial investigation for suspected peanut allergy giving urticaria and angioedema
Skin prick test
What allergic diseases will present in infancy and childhood
Dermatitis
Food allergy
Presentation of IgE allergic responses
Within 3-4 hours after exposure
Skin-angioedema, urticaria
Resp tract- cough, wheeze, nasal congestion
GI- D&V
Blood vessels- fainting, sense of impending doom
What is refractory anaphylaxis
No improvement in resp and cardio symptoms in response to 2 doses of IM adrenaline
What is the best lab test to diagnose anaphylaxis
Mast cell tryptase taken 30mins-2 hours after the initial symptoms start
What demotes a positive skin prick test
Wheal 3mm greater than negative control
What do sensitisation blood tests do
Detect IgE to whole allergen or a component of the allergen
What is function of compnoent resolved diagnostics
Test for IgE against the specific protein within a whole allergen
In essence identifies the exact protein to which someone is allergic to
How are allergic diseases diagnosed
Is made by a clinican based on epidemiology, history, exam, skin prick test (SPT) etc NOT a blood sensitisation test
These are necessary but not sufficient
If have a raised mast cell tryptase which fails to return to baseline afer anaphylaxis what could be causes
Systemic mastocytosis
Hereditary alpha tryptassaemia
What is gold standard for diagnosing food and drug allergies
Double blind oral food challenge tests
Anaphylaxis guidelines
ABCDE
Call for HELP
Remove trigger
Lie patient flat
IM adrenaline in anterolateral aspect of thigh
Establish airway and give oxygen
If no response
-IM adrenaline
- fluid bolus
Difference between food allergy and food intolerance
Allergy- adverse health effect arising from a specific immune response
Food intolerance- non-immune reactions which include pharmacological, metabolic
Examples of food intolerances
Food poisoning
Enzyme deficiencies- lactase
Pharmacological- caffeine, tyramine
Allergy mechanism in atopic dermatitis
IgE
Allergy mechanism in contact dermatitis
T cell mediated
What can differentiate between IgE sensitisation and IgE mediated allergy
Component resolved diagnostics
What can give delayed food induced anaphylaxis
Occur 3-6 hours after eating red meat
IgE antibody to alpha-1-3-galactose
What is the mechanism of oral allergy syndrome
When have hayfever, get cross reaction to some homologous proteins in apples, pears, carrots and nuts but not cooked
Presentation of oral allergy syndrome
Swelling and itch of lips and mouth
What does a positive blood sensitisation/SPT suggest
Sensitisation not allergy!
Most commmon cause of secondary immunodeficiency worldwide
Malnutrition
Causes of secondary immunodeficiency
Malnutrition
Measles- get immune defects lasting months to years
TB
HIV
COvid
Haem cancers
Drugs
Drugs which cause immunodeficiency
Steroids
Cytotoxic agents- methotrexate, mycophenolate, cyclophosophamide, azathioprine
Calcineurin inhibitors- cyclosporine, tacrolimus
Anti-epileptics
DMARD
JAK inhibitors
Biologics
What is goods syndrome
Combined T and B cell defect with thymoma and antibody deficiency
What infections are those with Goods syndrome susceptible to
CMV
PJP
Mucocutaneous candida
Natural history of HIV
Acute phase where can have flu like illness
Asymptomatic but progressive
AIDS
Difference in transmission of HIV across disease course
Related to viral load in plasma
High in acute and aids but drops in asymptomatic
What is acute immune response to HIV
Induction of HIV-1 antibodies
CD8 T cell activation
How is HIV diagnosed if under 18 months
HIV RNA or DNA tests
What tests are done which can determine HIV treatment
Test for HLAB5701 to avoid prescribing abacavir as severe risk of SJS
Tropism test for CCR5 to determine if CCR5 antagonist therapy would work
What is first line for HIV in the UK
2 NRTI and 1 NNRTI
OR
2NRTI and INI
Mainly will change treatment due to drug toxicity rather than response
When likely to see PJP, toxoplasma and mycobacterium avium complex in HIV
PJP- CD4 less than 200
Toxoplasma- 100
MAC- 75
What is chronic benign neutropenia
Get a mild/moderate neutropenia common in african and middle eastern groups
Asymptomatic with no further investigation required
What is familial neutropenia
Adult onset severe neutropenia
Specific organ autoimmune disease
No increased infection risk
Which conditions give a severe congenital neutropenia
Kostmann syndrome
Cyclic neutropenia
What is genetic defect in cyclic neutropenia
Autosomal dominant- Neutrophil elastase
What is genetic defect of Kostmann syndrome
Autosomal recessive- HCLS-1 associated protein X-1 which prevents maturation of neutrophils
How do severe congenital neutropenias present
Present in first 3 months
Susceptible to oral, cutaneous and epithelial s. aureus infections, g-enteric bacteria and fungal infections
How are severe congenital neutropenias treated
G-CSF support
Stem cell transplantation
Pathophysiology of neutrophil leukocyte adhesion deficiency
Deficiency in CD18 which is used to remove neutrophils from circulation
What is result of luekocyte adhesion deficiency
delayed separation of umbilical cord
very high neutrophil counts in blood (20-100 x106/L)
Absence of pus formation
Pathophysiology of chronic granulomatous disease
Deficiency in NADPH oxidase which used to generate free radicals as such fail to kill certain bacteria
Get excessive inflammation from persistent recruitment of neutrophils and phagocytes causing granuloma formation
Presentation of chronic granulomatous disease
Granulomas
Hepatomegaly and lymphadenopathy
THINK: PLACESS where you don’t want granulomas
Recurrent infections from PLACESS often affecting skin
Pseudomonas
Listeria
Aspergillosis
Candida
Ecoli
S aureus
Serratia
Treatment of chronic granulomatous disease
Interferon gamma
Test for chronic granulomatous disease
Dihydrorhodamine (DHR) flow cytometry test. DHR is oxidized to rhodamine, which is strongly fluorescent, following interaction with hydrogen peroxide.
What are the 3 triggers for complement pathway
Immune complexes (antigen-antibody)
Bacterial endotoxin
Mannose binding lectin
How does classical complement system work
Immune complexes trigger C1 which begins cascade involving C1, C2 and C4. Ultimately activate C3
Pathophysiology of classical component deficiencies
These include deficiencies in C1q,2 and 4
This means that is failure to activate the complement system causing increased susceptibility to infections
What is link of classical complement deficiencies and SLE
If have deficiency of classical complement pathway then is accumulation of immune complexes which can deposit in the joints, skin and kidneys
Presentation of classical complement deficiencies
Susceptibility to infections namely Hib and strep pneumoniae
Severe skin disease
Co-existing SLE
Pathophysiology of alternative pathway deficiencies
Lack of factor B, D and P (properdin) mean less activation of terminal pathway from alternative pathway
Susceptibility of alternative pathway deficiencies
Encapsulated bacteria
Presentation of C3 deficiency
Increased suscpetibility to encapsulated bacteria infection
What are the types of C3 deficiency
Primary from genetic deficiency
Secondary- get autoantibodies against C3
What is associated with C3 deficiency
Membranoproliferative glomerulonephritis
What is significance of mannose binding lectin deficiency
Very common however does not affect susceptibility to infection unless coinciding factor causing immunodeficiency like chemo or premature infant
Pathophysiology of Severe Combined ImmunoDeficiency (SCID)
Encompassing term for various mechanistic pathways however all relate to defects in the generation of lymphoid precursors in the bone marrow
Presentation of SCID
Present by 3 months of age
Opportunistic infections
Live vaccine infected (BcG and rotavirus)
Persistent candida infection
Failure to thrive
Peristent diarrhoea
Which infections are SCID normally susceptible
THINK: Opportunistic infections like in Goods Syndrome
Opportunistic- candida, PJP, CMV
Viral chest and GI infections- adenovirus, parainfluenza
RARELY BACTERIAL
Treatment for SCID
Stem cell transplant
Pathophysiology of DiGeorge syndrome
22q11 deletion
Congenital features of DiGeorge syndrome
CATCH
Cardiac abnormalities (TOF)
Atresia (oesophageal)
Thymic aplasia
Craniofacial defects (cleft palate)
Hypocalcaemia from hypoparathyroidism
Immune problems of DiGeorge syndrome
Thymic hypoplasia leading to reduced T cell counts
Increased incidence of autoimmune conditions and sino-pulmonary infections
How is IgA deficiency diagnosed
Serum IgA under 0.07g/L with normal Ig and B cell counts
Presentation of IgA deficiency
Most asymptomatic
Increased prevalence of allergic disorders and autoimmune diseases
Recurrent sino-pulmonary and GI infections
What is pathogenesis of common variable immune deficiency
Heterogenous conditions were is defect in B cell develpoment, maturation or function and fail to produce protective antibodies
Presentation of CVID
PRESENTS IN ADULTS
Recurrent sino-pulmonary infections with encapsulated bacteria
These can be so bad get bronchiectasis
Otitis media
Hib conjunctivitis
Enteric infections
Skin cellulitis, abscess HSV and VZV
Viral resp infections
Granulomatous infiltration
Autoimmune conditions common
Increased risk of B cell NHL and gastric cancers
Hallmarks of CVID
Increased infection susceptibility
Autoimmune conditions more prevalent
Granulomatous infiltration
Lymphoproliferative conditions common
Management of CVID
Normal human IVIG
Pathogenesis of X-linked agammaglobulinaemia
Mutation in bruton tyrosine kinase which is key in maturation of B cells
Presentation of x-linked agammaglobulinaemia
Presentation under 5
Recurrent bacterial infection of ENT, resp and GI
Encapsulated bacteria
Management of x linked agammaglobulinaemia
Normal human IVIg
Blood findings of x linked agammaglobulinaemia
Neutropenia
Reduction or absence of b cells
Absent of all Ig
MOst common cause of death in X linked agammaglobulinaemia
Acute or chronic lung disease
MOst common antibody deficiency
Selective IgA deficiency