Immuno Flashcards
Components of classical complement pathway
Activated by antigen-Ab immune complex
C1q –> C1
C2
C4
Define somatic hypermutation
Part of germinal centre reaction
B cell receptor edited on successive rounds of antigen engagement
Continues until very high affinity
Components of mannose-binding lectin complement pathway
MBL - directly binds to microbial cell surface carbohydrates
Stimulates classical pathway C2, C4 (NOT C1)
Define isotope switching
Part of germinal centre reaction
Switch from IgM to plasma cells secreting IgG, IgE or IgA
Components of alternative complement pathway
C3 - binds to bacterial cell wall components
Factors B, I, P
Components of final common complement pathway
C3 - all pathways converge here
C5-9
Membrane attack complex
Oxidative killing mechanism
NADPH oxidase complex converts O2 into reactive oxygen species – superoxide, hydrogen peroxide
Myeloperoxidase catalyses production of hydrochlorous acid (very potent antimicrobial/oxidant) from hydrogen peroxide + chloride
Non-oxidative killing mechanism
Release of bactericidal enzymes e.g., lysozyme, lactoferrin into phagolysosome
Each enzyme has unique antimicrobial spectrum –> broad coverage (bacterial + fungi)
Small molecule drugs causing secondary immune deficiency
Glucocorticoids & mineralocorticoids
Cytotoxic agents -
methotrexate, mycophenolate, cyclophosphamide, azathioprine
Calcineurin (IL-2) inhibitors -
cyclosporine, tacrolimus
Anti-epileptic drugs - phenytoin, carbamazepine, levetiracetam
DMARDs -
sulfasalazine, leflunomide
Good’s syndrome - mechanism & presentation
T cell defect (thymoma) + B cell defect (loss of Ab secretion, absent B cells)
Presents with:
CMV PJP
Muco-cutaneous candida
AI disease (due to lack of tolerance) - pure RBC aplasia, myasthenia graves, lichen planus
Patterns of Immunoglobulin deficiency
Isolated IgG reduction - prednisolone use (>10mg/day) or protein losing enteropathy
IgM & IgG reduction - B cell neoplasm, rituximab Tx
IgA & IgG reduction - primary Ab deficiency?
Investigations for secondary immune deficiency
FISH
Full blood count
Immunoglobulins - IgG, A, M, E
Serum complement - C3, C4
HIV test (18-80 yrs)
Indications for IgG replacement in secondary immunodeficiency
- Underlying cause of hypogammaglobulinaemia CANNOT be reversed OR reversal CONTRAINDICATED
OR
- hypogammaglobulinaemia associated with: drugs, monoclonal Abs targeted at B or plasma cells, post-HCST, NHL, CLL, MM or other B cell ca.
AND
3a. recurrent or severe bacterial infection despite continuous oral Abx for 6 months
3b. IgG <4
3c. Failure of response to pneumococcal/other polysaccharide vaccine challenge
Purpose of HLA-B*5701 blood test in HIV
Should avoid prescribing Abacavir in those with allele (~8% of NW London)
Risk of severe systemic hypersensitivity syndrome –> toxic epidermal necrolysis + liver toxicity
What factors influence the viral load ‘set point’ in HIV infection?
viral genotype
CD8 T cell immune response
Host genetics - HLA, CCR5 polymorphisms
Mechanism of ‘cure’ in Berlin/London patient?
Allogeneic stem cell transplant from CCR5 mutant HLA matched donor
Important infections & CD4 thresholds in HIV infection
Kaposi’s sarcoma - CD4 400
Pulmonary TB, herpes zoster, hairy leukoplakia - CD4 300-350
Pneumocystis jirovecii - CD4 200
Mycobacterium avid complex (MAC) disease - CD4 75
Innate primary immunodeficiencies of phagocytes:
Conditions with failure to produce neutrophils + their mechanism?
Reticular dysgenesis (severe SCID) - failure of stem cells to differentiate along myeloid or lymphoid lineage (so also an ADAPTIVE condition)
kostmann syndrome - specific failure of neutrophil maturation
cyclic neutropenia - specific failure of neutrophil maturation
Innate primary immumodeficiencies of phagocytes:
Conditions with defect of phagocyte migration + mechanism?
Leucocyte adhesion deficiency - neutrophil failure to exit bloodstream due to deficiency of CD18 beta-2-integrin subunit
Innate primary immunodeficiencies of phagocytes:
Condition with failure of oxidative killing?
Chronic granulomatous disease
- NADPH oxidase component deficiency = absent respiratory burst
- persistent neutrophil/macrophage accumulation + failure of antigen degradation = excessive inflammation, granuloma
Innate primary immunodeficiencies of phagocytes:
Conditions with cytokine deficiency + mechanism?
IL12, IL12R, IFN-y, IFN-y-R deficiencies
Cytokine network important for mycobacterial defence so deficiency = TB, atypical mycobacteria infections
Investigation results in innate primary immunodeficiencies of phagocytes
Kostmann syndrome - absent neutrophils, normal leucocyte adhesion markers, no neutrophils for NBT/DHR test
leucocyte adhesion deficiency - increased neutrophils (during infection), absent CD18, normal NBT/DHR test
Chronic granulomatous disease - normal neutrophils, normal leucocyte adhesion markers, abnormal NBT/DHR test
IL-12/IFN-y pathway deficiency - all normal
Treatment of innate primary immunodeficiencies
Prophylaxis:
- vaccination
- abx?
Aggressive Tx of infections
- abx e.g. septrin
- antifungs e.g. itraconazole
- antivirals e.g. acyclovir
Definitive = haematopoetic stem cell transplantation
Specific Tx:
- interferon gamma therapy for chronic granulomatous disease
- cytokines to stimulate NK cytotoxic function
Innate primary immunodeficiencies of NK cells:
Conditions + mechanism?
Classical NK deficiency - Absence of NK cells in peripheral blood, GATA1 or MCM4 gene abnormalities
Functional NK deficiency - NK cells present but abnormal activity,
FCGR3A gene abnormality
Innate primary immunodeficiencies of complement:
Conditions + presentation
Complement deficiency (C5-9, Properidin) - bacterial infections esp encapsulated, Neisseria meningitides
Classical pathway deficiency (C2, C1q) - susceptibility to SLE (failure to clear dead cells + immune complexes)
MBL deficiency - mutations common, does not usually cause disease
NOTE: SLE can also cause complement deficiency - uses up components + forms autoantibodies against C3
Investigation results in innate primary immunodeficiencies of complement
C1q deficiency - C3+, C4+, CH50-, AP50+
Properidin deficiency - C3+, C4+, CH50+, AP50?
C9 deficiency - C3+, C4+, CH50-, AP50-
(SLE - C3+/-, C4-, CH50+/-, AP50+)
Adaptive primary immunodeficiencies - SCIDs
Condition + mechanism?
Reticular dysgenesis - failure of myeloid + lymphoid differentiation, most severe SCID, also INNATE condition
X-linked SCID - inability to respond to cytokines arrests T, NK & B cell development, mutations of common gamma chain
Other SCIDs - various pathways e.g. cytokine receptor, signalling molecule, metabolic
ADA deficiency - very low/absent T, NK and B cells, mutation in ADA enzyme needed for lymphocyte metabolism
Phenotype of severe combined immunodeficiency (SCID)
Presents ~ 3 months - before this, protected by passive transfer of maternal IgG across placenta/in colostrum
Infections
Failure to throve
Persistent diarrhoea
Skin disease - colonisation of empty BM by maternal lymphocytes (form of GvHD)
Personal/family Hx early infant death
Adaptive primary immunodeficiencies of T cells:
Condition + mechanism?
22q11.2 deletion syndrome (Di George) - failure of T cell maturation in underdeveloped thymus + syndromic features
MHC Class II deficiency (Bare lymphocyte type 2) - MHC class II molecules absent on cells, profound CD4+ T cell deficiency, normal B cell numbers but cannot produce IgA/IgG (need CD4 help for this)
MHC Class I deficiency - same features but low CD8+ T cells
T cell effector defects - variable e.g. IFN production, cytotoxicity, T/B cell communication
Investigation results in Adaptive primary immunodeficiencies of T cells
SCID: CD4-, CD8-, B cells+/-, IgM+/-, IgG-
DiGeorge (22q11.2): CD4-, CD8-, B cells+, IgM+, IgG-
Bare lymphocyte type 2/MHC Class II deficiency - CD4-, CD8+, B cells+. IgM+. IgG-
Treatment of adaptive primary immunodeficiencies
Aggressive prophylaxis + Tx of infections
Haematopoietic stem cell transplant
Specific:
- PEG-ADA enzyme replacement for ADA SCID
- thymic transpant (cultured donor tissue into quadriceps) for DiGeorge
- immunoglobulin replacement (B cell types)
- immunisation for selective IgA only (other B cell types cannot mount IgG response)
Adaptive primary immunodeficiencies of B cells
Condition + mechanism?
Bruton’s X linked hypogammaglobulinaemia - preB cells cannot develop into mature B cells, no IgG production, abnormal B cell tyrosine kinase
Hyper IgM syndrome - no germinal centre development, failure of isotype switching, CD40 ligand mutation
Common variable immune deficiency - heterogeneous, low IgG (+ others), poor response to immunisation
Selective IgA deficiency - cause unknown, only 1/3 symptomatic
Investigation results in adaptive primary immunodeficiencies of B cells
Bruton’s X linked: CD4+, CD8+, B cell-, IgM-, IgG-, IgA-
Hyper IgM: CD4+, CD8+, Bcell+, IgM++, IgG-, IgA-
Common variable immune deficiency: CD4+, CD8+, Bcell+, IgM+, IgG-, IgA-
Selective IgA deficiency: CD4+, CD8+, B cell+, IgM+, IgG+, IgA-
CD4+ T cell effector subsets (and their polarising cytokines)
IL-12 & IFN-y produce Th1
IL-6 & TGF-b produce Th17
TGFb produce Treg
IL-6, IL-1b, TNFa produce TFh
IL-4, IL-6 produce Th2
Treatment of T cell mediated Transplant rejection
Steroids!!
- methylprednisolone 3x pulses IV 60mg/kg
- 3 days in a row
- followed by oral taper
Anti-thymocyte globulin - ATG/OKT3
Treatment of B cell mediated rejection
Remove Abs- plasma exchange
IV Ig
Anti CD5?
Anti CD20
How does route of allergen exposure affect outcome?
Oral exposure promotes immune tolerance
Skin & respiratory exposure promotes sensitisation (specific IgE formation)
Monogenic auto inflammatory disease
Familial Mediterranean fever
TNF receptor associated periodic syndrome (TRAPS)
Muckle Wells syndrome
Hyper IgD with periodic fever syndrome (HIDS)
Polygenic auto inflammatory disease
IBD - Crohn’s disease, Ulcerative colitis
Osteoarthritis
Giant cell arteritis
Takayasu’s arteritis
Monogenic auto-immune disease
APS-1
APECED
ALPA
IPEX
Polygenic autoimmune disease
Rheumatoid arthritis SLE Myaesthenia gravis Pernicious anaemia Graves' disease Primary biliary cirrhosis ANCA associated vasculitis Goodpasture disease
Complication of familial Mediterranean fever?
AA amyloidosis
Excess serum amyloid A produced due to inflammation
Deposits in kidneys, liver, spleen
Presents with nephrotic syndrome (proteinuria) + renal failure
IPEX clinical features
‘Diarrhoea, diabetes & dermatitis’
Pancreas autoAbs –> DM
Thyroid autoAb –> hypothyroidism
Enteropathy
ALPS (Auto-immune lymphoproliferative syndrome) clinical features
Large spleen, lymph nodes
AI disease - esp cytopenias
Lymphoma
Genetic polymorphisms/associations in Polygenic Autoimmune disease
T cell activation polymorphisms:
PTPN 22 - SLE, Rh arthritis, T1DM
CTLA4 - SLE, AI thyroid disease, T1DM
HLA susceptibility alleles:
HLA-DR15 - Goodpasture’s disease
HLA-DR3 - Graves’ disease, SLE, T1DM
HLA-DR4 - T1DM, Rh arthritis
Gel & Coomb’s Hypersensitivity Reactions
Type 1 = Anaphylactic, immediate, IgE mediated
Type 2 = cytotoxic, Ab reacts with cellular antigen
Type 3 = immune complex, Ab reacts with soluble antigen to form complex
Type 4 = delayed, T cell mediated
Autoantigens/Abs in Type II Hypersensitivity Auto-immune disease
Goodpasture = non Collagenous domain of basement membrane collagen type IV
Pemphigus vulgaris = epidermal cadherin
Graves’ = Thyroid stimulating hormone (TSH) receptor
Hashimoto’s thyroiditis = anti-thyroid peroxidase (TPO), anti-thyroglobulin
Myaesthenia gravis = Acetylcholine receptor
Pernicious anaemia = Anti Intrinsic factor, anti gastric parietal cell
Autoantigens/Abs in Type 3 Hypersensitivity Autoimmune disease
SLE = all Antinuclear Abs
Specifically:
- dsDNA!! highly specific, useful to identify relapse
- Extractable nuclear antigens: Ro, La, Sm, ribonucleoproteins (RNP) may occur, also found in Sjogren’s, not useful for disease monitoring
- topoisomerase Scl70
- centromere
Autoantigens/Abs in Type 4 hypersensitivity Autoimmune disease
T1DM = Anti islet cell, anti-insulin, anti-GAD, anti-IA2
3-4 Abs = highly likely to develop disease (but not used for Dx)
Key features of Goodpasture’s syndrome (clinical & Ix)
Clinical:
- Haemoptysis, pulmonary haemorrhage
Ix:
- Biopsy –> crescentic glomerulonephritis
- Urine dip –> microscopic haematuria, proteinuria
- Immunofluorescence –> linear Ab position along glomerular basement membrane
Other important autoantigens/Abs
Coeliac = anti TTG, anti-endomysial
AI hepatitis = antinuclear (ANA), smooth muscle (SMA), anti-liver kidney microsomal proteins (anti-LKM), anti-neutrophil cytoplasmic antibody perinuclear staining (pANCA)
Primary biliary cholangitis = ANA, antimitochondrial (AMA), pANCA
Microscopic polyangiitis / Eosinophilic granulomatosis with polyangiitis = pANCA
Granulomatosis with polyangiitis = cANCA (cytoplasmic staining)
Investigations for Antiphospholipid Syndrome
Lupus anticoagulant - cannot be assessed if taking anticoagulant Tx
Anti-cardiolipin Ab
Anti-B2 glycoprotein 1 Ab
Clinical Features of Limited Cutaneous Systemic Sclerosis
CREST Calcinosis Raynaud's Oesophageal dysmotility Sclerodactyly Telangiectasia
+ primary pulmonary HTN
Clinical Features of Diffuse cutaneous systemic sclerosis
CREST features plus:
more extensive GI disease
Interstitial pulmonary disease
Scleroderma of kidney –> renal crisis
Skin involvement progresses beyond forearms (unlike CREST)
Autoantibodies seen in Systemic Sclerosis
Extractable nuclear antigen +ve
Specifically:
Limited = anti centromere
Diffuse:
- anti topoisomerase Scl70
- RNA polymerase
- Fibrillarin
Autoantibodies seen in Idiopathic inflammatory myopathy
Anti-aminoacyl transfer RNA synthetase Ab e.g. Jo1 (cytoplasmic)!!
Others:
ANA - some patients
Anti-signal recognition peptide Ab (nuclear & cytoplasmic)
Anti-Mi2 (nuclear) - more in dermatomyositis vs polymyositis
What cytokine drives clonal expansion of T cells following antigen exposure?
IL-2
Live vaccines
MMR BCG Yellow fever Typhoid (oral) Polio (Sabin oral) Influenza (Fluenz tetra for children 2-17yrs)
Inactivated vaccines
Influenza (inactivated quadrivalent) Cholera Bubonic plague Polio (Salk) Hep A Pertussis Rabies
Component/subunit vaccines
Influenza (recombinant quadrivalent) - less common
HPV - uses capsid
Hep B (HbSAg)
Toxoid vaccines
Diphtheria
Tetanus
Conjugate vaccines
Haemophilus Influenzae B
Meningococcus
Pneumococcus (Prevenar)
Which primary antibody deficiencies are treated with human normal Ig?
X-linked agammaglobulinaemia
X linked hyperIgM syndrome
Common variable immune deficiency
Examples of specific human immunoglobulin Tx?
Hep B - following needle stick, bite, sexual contact (with HepBSAg +ve individual)
Rabies - injected around bite site
Varicella Zoster - women <20 weeks pregnant OR immunosuppressed + acyclovir/valaciclovir contraindicated
Important monoclonal Abs & their targets
Ipilimumab = anti CTLA-4 - advanced melanoma
Nivolumab = anti PD-1 - advanced melanoma, renal cell ca.
Important cytokine-based Tx
PRO-IMMUNE:
Interferon gamma = Chronic granulomatous disease (neutrophil immunodeficiency)
Interferon alpha = Classical or Functional NK deficiency, Hep B or C (with ribavirin)
IL-2 = renal cell ca.
PRO-REGULATION:
Interferon alpha 2a = Behcet’s
Corticosteroids MOA
On prostaglandins:
- inhibits phospholipase A2
- less Arachidonic acid –> less leukotrienes, prostaglandins
- less inflammation
On phagocytes:
- decreased expression of adhesion molecules on endothelium –> less immune cell traffic to tissues
- decreased phagocytosis
- decreased release of proteolytic enzymes
On lymphocytes:
- sequestration in lymphoid tissue
- blocks cytokine gene expression
- decreased Ab production
- promotes apoptosis
Cyclophosphamide side effects
- BM depression
- hair loss
- irreversible infertility (M>F)
- haemorrhagic cystitis
- malignancy: bladder, haemolytic, non melanoma skin ca.
- Pneumocystis jiroveci infection
Azathioprine side effects
BM suppression
- TPMT polymorphism = unable to metabolise azathioprine so check before starting!
- always check FBC before starting
Hepatotoxicity
- uncommon
Infection - but less than cyclophosphamide
Mycophenolate mofetil side effects
BM suppression
Infection - herpes reactivation, progressive multifocal leukoencephalopathy (JC virus)
Indications for plasmapharesis
Goodpasture syndrome
Severe acute myaesthenia gravis
Antibody mediated transplant rejection / ABO incompatibility
Indications for Calcineurin inhibitors
E.g. ciclosporin, tacrolimus
Transplantation
SLE
Psoriatic arthritis
including during pregnancy
Indications for mTOR inhibitors
E.g. Rapamycin, Sirolimus
Transplantation
Tacrolimus/Ciclosporin MOA
Calcineurin inhibitors
Inhibit T cell proliferation/function (via reduced IL-2 expression)
Indications for JAK inhibitors
Rh arthritis
Psoriatic arthritis
Axial spondyloarthritis
Indications for PDE4 inhibitors
E.g. Apremilast
Psoriasis + Psoriatic arthritis
Basiliximab MOA + Indication
Directed at IL-2 R alpha chain of CD25 ‘anti CD25’
Bocks IL2 signalling –> inhibits T cell proliferation
Prophylaxis of allograft rejection
Abatacept MOA + indication
CTLA-4 Ig fusion protein
Reduces co-stimulation of T cells via CD28 (opposite of Ipilimumab used in melanoma)
Rheumatoid arthritis
Rituximab MOA + Indications
Anti-CD20 specific Ab –> depletes mature B cells
Lymphoma
Rh arthritis
SLE
Vedlizumab
Specific Ab for alpha-4-beta-7 integrin
Inhibits MadCAM1 binding to a-4-b7 integrin = failure of leucocyte migration + extravasation to tissue
‘Ved’ = Fed = Tx for IBD
TNF-alpha Antibodies
‘IACG’
Infliximab
Adalimumab
Certolizumab
Golimumab
Etanercept MOA + Indications
Inhibits TNF alpha and TNF beta
Rh arthritis
Ank Stond
Psoriasis & Psoriatic arthritis
Indications for IL-1 blockade
Familial Mediterranean Fever
Gout
Adult onset Stills disease
IL-6 Antibodies + Indication
Tocilizumab
Sarilumab
Rh arthritis
(Castleman’s disease)
Guselkumab MOA + Indication
Targets p19 alpha subunit of IL-23 ‘anti IL23’
Psoriasis & psoriatic arthritis
Indications for IL-4, 5, 13 blockade?
Asthma & eczema
Denosumab MOA + Indication
Anti-RANK ligand Ab
Osteoporosis
