Immunology Flashcards
IFN1alpha and beta
Produced by virus infected cells
Interferon response
Induce resistance to viral replication in surrounding cells
Induce expression of ligands recognised by NK receptors
Activate NK cells to kill
CXCL8/IL8
Secreted by local Mphage
Recruit and activate neutrophils, basophils and T cells to site of infection
Causes LFA-1 integrin to change to high affinity binding state + forms gradient for neutrophil in migration by sticking to extracellular matrix
IL-12
Produced by local Mphage
Activates NK cells and causes their proliferation
Induces CD4+ to differentiate into Th1 cells
IFN-gamma
Produced by activated NK cells and CD8+ T
Activates macrophages and upregs killing capacity
Th1 promoter
Induces expression of vascular adhesion molecules
IL6
Lymphocyte activation
Increased antibody production
Feber
Stim hepatocytes to release acute phase proteins including CRP and fibrinogen
Induces differentiation of CD4 cells into Th17 or Tfh
CRP
Opsonin and complement activation
Fibrinogen
Fibrin clot formation
Prostaglandins
Made by COX pathway
Induce vascular permeability, vascular dilation, neutrophil chemotaxis
Thromboxane
Made by COX pathway
Induce platelet aggregation and blood vessel constriction
PAF
Platelet activating factor
Lipooxygenase pathway from arachidonic acid
Induce platelet activation, eosinophil chemotaxis, neutrophil activation
Leukotrienes
Lipooxygenase pathway from arachidonic acid
Induce bronchial smooth muscle contraction, neutrophil chemotaxis, slow reacting substance of anaphylaxis SRS-A
How do you induce phagocytosis?
- C3b binds to CR1 (or CR3) and
2. C5a binds to C5AR1
What clinical condition do you get from low CR1 levels and why?
Immune complex disease
Normally highly expressed on erythrocytes, where they bind immune complexes and take them to be cleared by the liver
What is MBL?
Mannose binding lectin
Collectin with collagen and lectin domains
Soluble PRR - binds mannose and fucose round on microbial surfaces of pathogen
Activates complement via lectin pathway
Which complement components are involved in the alternative pathway?
C3
C3H2OBb = fluid phase C3 convertase
C3bBb = alternative pathway C3 convertase
Which complement components are involved in the lectin pathway?
MBL, MASP1 and 2 C4 C2 C3 C4bC2a = classical C3 convertase
Which complement components are involved in the classical pathway?
C1 (q, then r and s) C4 C2 C3 Uses C4bC2a = classical C3 convertase
Which complement components are involved in the membrane attack complex?
C3b2Bb = alternative C5 convertase
C4bC2aBb = classical pathway c5 convertase
C5b
C5b67
C5b678
C5b6789
Used against gram - bacteria and enveloped viruses
Properdin
Positive regulator alternative pathway
Stabilises C3bBb and C3b2Bb (MAC formation)
Factor I
Negative regulator
Constitutively active serine protease that degrades C3b and C4b
Requires MCP and factor H cofactors
Membrane cofactor protein
Induces dissociation of C4bC2a (lectin and classical pathways) and C3bBb (alternative) by factor I
Complement receptor 1
Negative regulator of complement cascades
Decay accelerating capacity and factor I cofactor activity
Induces dissociation of C4bC2a (lectin and classical pathways) and C3bBb (alternative) by factor I
Mediates phagocytosis
Immune adherence (to clear Ab-Ag complexes)
Factor H
Main control factor to PROTECT THE HOST
Soluble cofactor for factor I
Attaches to sialic acid present on host membranes, but absent from most bacteria
Causes dissociation of C3bBb and makes C3b susceptible to cleavage by factor I
DAF
Decay accelerating factor
Present on host cells
Dissociates the classical and alternative C3 convertases (Bb leaves)
Protectin
Cell surface protein, binds MAC intermediate C5b678, prevents insertion into membranes
Also interacts with C9 and prevents its recruitment to the MAC complex
C1-4 defects?
Immune-complex disese, infection
C3 defect?
Susceptibility to infection by pyogenic bacteria (encapsulated bacteria) as C3 is an important opsonin
e.g. Staph or strep
C5-9 defect?
MAC component defects
Lack of complement mediated lysis
Recurrent Neisseria infections
Factor D/properdin defect?
Can’t make C3b. Less opsonisation and phagocytosis. So control of encapsulated/pyogenic bacteria compromised, especially N. meningitides
Factor I, Factor H defect?
Depletion of C3 due to uncontrolled alternative pathway activation leads to susceptibility to pyogenic infections especially N. meningitides
DAF/protectin defect?
What can it be due to?
GPI-anchored proteins so due to reduced GPI synthesis
On RBCs
Causes paroxysmal nocturnal hemoglobinuria - complement mediated lysis of RBCs
How does S. Aureus evade complement?
- Protected by polysaccharide capsule to prevent opsonisation
- SCIN Staphylococcus Complement Inhibitor binds and inactivates C3 convertases if they do assemble, so opsonins aren’t generated
- Secretes proteins that bind or degrade and inactivate C3
- Secretes staphylococcal protein A that binds the Fc region of IgG blocking complement recruitment and activation
- Recruit host inhibitor factor I to bacterial surface by clumping factor A
- Chemotaxis inhibitory protein blocks C5a chemotactic receptor on neutrophils limiting their recruitment
- Other proteins interfere with neutrophil extravasation to the site of infection
What are TLRs and how many do we have?
They are pattern recognition receptors
We have 10
First PRRs to be discovered
What do TLRs trigger?
- Signalling adaptor molecule MyD88
- Downstream signalling events - BACTERIA activate NF-kappaB, AP-1 (a TF) - PRO INFLAMMATORY, and VIRUSES IRFs interferon-regulatory factors - ANTI-INFLAMMATORY
- Release of products including inflammatory cytokines, IFN-1, chemokines, antimicrobial peptides
- Dendritic cell maturation
- Induction of adaptive immune response
Which TLRs are on the cell surface? What do they recognise in general?
1245610
Microbial lipids EXCEPT TLR5 - flagellin
–> NF-kappaB, AP-1 pro-inflammatory
Which TLRs are in endosomes? What do they recognise in general?
3789
Nucleic acids - dsRNA, ssRNA, DNA –> viral IRF interferon response anti-inflammatory
What does TLR1 recognise?
TLR1/2 heterodimer
PAMP: Triacyl lipoproteins (on gram - bacteria)
What does TLR2 recognise?
and TLR2/6 and TLR2/1 heterodimer PAMP: Peptidoglycan (gram +) Zymosan (yeast, fungi) Diacyl lipoproteins, GPI-linked proteins (trypanosomes) DAMP: HSP, HMGB-1, urate crystals
What does TLR3 recognise?
PAMP: dsRNA viral
DAMP: mRNA necrotic cells
What does TLR4 recognise?
PAMP: LPS
DAMP: HSP, HMGB-1, oxidised LDL from chronic inflammation of arterial wall in atherosclerosis
What does TLR5 recognise?
PAMP: Flagellin
What does TLR6 recognise?
TLR2/6 heterodimer
PAMP: Diacyl lipopeptides (gram +)
Zymosan (yeast/fungi)
DAMP: oxidised LDL from chronic inflammation of arterial wall in atherosclerosis
What does TLR7 recognise?
PAMP: ssRNA virus
DAMP: ssRNA
What does TLR8 recognise?
PAMP: ssRNA virus, phagocytosed bacterial RNA
DAMP: ssRNA, microRNA
What does TLR9 recognise?
PAMP: unmethylated CpG-DNA (bacterial DNA)
DAMP: Self-DNA, HMGB-1
What does TLR10 recognise?
????
Name some PRRs and what they detect.
TLRs - bacterial and viruses that replicate in endosomes mainly
CLR C-type lectin receptors (fungal infections)
RLRs RIG-I-like receptors (viral RNA in the cytoplasm)
NLR Cytosolic NOD-like receptors (cytoplasmic receptors that recognise both PAMPs and DAMPs)
NOD1 NOD2 = recognise fragments of peptideoglycan from bacteria
NOD2 = muramyl dipeptide released from gut microbiota, role in gut homeostasis. Mutations associated with Crohn’s disease
NLRP3/NALP3 - peptidoglycan, bacterial DNA, ATP, toxins, dsRNA. Part of inflammasome
What is the inflammasome?
Large cytosolic structure
Linked to diseases - atherosclerosis, gout, Type 2 diabetes
NLRP3 involved - detect peptidoglycan, bacterial DNA, ATP, toxins, dsRNA
Induce inflammation by causing caspase 1 –> IL-1beta
Triggered by cholesterol, monosodium urate (Gout) TXNIP (related to hepatic glucose production in T2Diabetes)
IL-1beta?
Formed by caspase 1 caused by inflammasome
Activates lymphocytes, local tissue destruction, increases access of effector cells
Activates vascular endothelium - induces E-selectin
Leads to fever and production of IL6
Examples of DAMPs?
HMGB-1, ATP, DNA, RNA, ECM components uncovered by tissue damage, HSPs
Purpose of the acute inflammatory response?
Basically = recruit exudate
- Dilate blood vessels (Histamine, TNF-alpha, prostaglandins, leukotrienes)
- Increase permeability of vessel wall
- Recruit cells (leukocytes, neutrophils initially, then monocytes, some infections eosinophisl and plasma cells)
What are the endogenous pyrogens?
IL-1, IL-6, TNF-alpha, IFN-gamma
Which cytokines promote cellular immunity/Th1?
IFN-gamma, IL-12
Which cytokines promote humoral immunity/Th2?
IL4, IL10
Which cytokines are non-inflammatory?
TGF-beta, IL4, IL10
What do macrophages secrete?
- Cytokines - IL-1beta, TNF-alpha, IL-6, CXCL8, IL-12
2. Prostaglandins and leukotrienes
TNF-alpha
Triggered by IgE and IgG cross-linking
1. Activates vascular endothelium
2. Increases vascular permeability
Increased IgG, complement and cell entry to tissues
3. Increased platelet adhesion to blood vessel wall
4. Fever,
5. Mobilisation of metabolites
6. E-selectin appears
7. Induce prostaglandin synthesis in the hypothalamus8. Can result in shock
Which receptors on neutrophils help their recruitment and what do they bind to?
- Sialyl-Lewis X (to P and then E selectin - vessel) for rolling/weak tethering
CXCL8 receptor -nphil - LFA-1 - nphil to ICAM-1 for tight adhesion - wall
- then CD31 on endothelium for diapedesis NB also elastase
- follows CXCL8 gradient
What is LAD?
Leukocyte adhesion deficiency
Rare immunodeficiency caused by defect in the recruitment of neutrophils due to CD18 defect (beta chain of LFA-1).
Results in recurrent life threatening bacterial infection in infants
How are monocytes recruited?
24h later VLA4, the monocyte integrin binds to VCAM1 (endothelial adhesion molecule upreg more slowly)
What is the pathophysiology of septic shock?
Burns/widespread endotoxins like LPS –> macrophages in liver and spleen release TNF alpha –> widespread vasodilation –> loss of blood pressure and heart failure (septic shock) and disseminated intravascular coagulation (blood clotting in the small vessels) –> loss of perfusion so major organ failure
Also massive consumption of clotting proteins –> lack of clotting capacity in the blood and bleeding
Why might chronic inflammation occur?
- Injurious agent endogenous e.g. stomach acid
- Injurious agent may be non-degradable e.g. silica
- Injurious agent may evade host defences e.g. TB
- Host may attack itself e.g. RA autoimmunity
How does an antibody work?
- Neutralisation
Blocking biological activity of a target molecule e.g. a toxin - Opsonisation
Ab coated Ag interact with specific receptors, e.g. on macrophages, allowing them to recognise an Ag more efficiently. - Complement activation
Ab coated Ag may cause direct lysis by recruiting complement - classical pathway
How do lymphocytes enter lymph nodes?
Through specialised endothelia called high endothelial venules
How do follicular dendritic cells trap antigen in B cell area?
In complexes of Ag/Ab/C3b
How do dendritic cells enter the lymph node?
Afferent lymphatic
How many constant domains do each type of antibody have?
IgG, A, D = 3
IgM, E = 4
Where is the flexibility of an antibody?
Hinge region and V-C junction (like a ball and socket joint)
How do antigen binding sites vary?
3 complementarity determining regions CDRs
CDR3 most variable
How are CDR1, 2 and 3’s variations generated in heavy chains?
Somatic recombination of 38-46 genes for variable region - CDR 1 and 2
23 for diversity, 6 for joining - together = CDR3, plus the junctions between rearranged V D and J
How is diversities generated in light chains?
Somatic recombination for V then J of first kappa (34-38 V and 5 J) then lambda (29-33 V then 4-5J)
How is antibody diversity achieved?
- Different light and heavy chain combinations
- Different VDJ segments
- Junctional diversity
- Somatic hypermutation
How is junctional diversity achieved and what is the point?
Terminal deoxynucleotide transferase (TdT) addition, addition due to recombination mechanism, deletion
Point = variation! can change between reading frames, add stop codons etc.
How does the B cell undergo somatic hypermutation and where does it do it?
Antigen driven so in lymph nodes
Daughter cells of B cells undergo numerous (1/1000) point mutations, including C –> U deamination by AID activation induced cytidine deaminase
If new receptor isn’t an improvement, doesn’t get T cell help
What does the enzyme AID do?
Somatic hypermutaiton, isotype switching
What does alternative splicing offer to Ab generation?
- produces IgM and IgD initially
- can choose different polyA sites to either generate soluble or membrane bound Ig
Which Ig has the highest serum level?
IgG1
Which Ig has the longest and shortest half life?
Longest = IgG1, IgG4
Shortest - IgE
Which Ig can transfer across the placenta?
IgG
Which Ig activate complement?
IgM IgG123, IgA
Which Ig bind to the Fc of the macrophage?
IgG1, IgG3, IgG4, IgA, IgE
Which Ig mainly binds to mast cells?
IgE
What are the different subsets of Fc receptor and what is their function?
Effector function of Ab, deliver antibody to different sites and link antigen to molecules or cells
1. High affinity
RI Kd 10^-9, bind monovalent Ab/Ag complexes
2. Low affinity FcgammaRI or II, Kd 10^-6, bind multivalent Ab/Ag complexes
FCgammaRI?
High affinity for IgG
On macrophage, activated PMN
phagocytosis and respiratory burst neutrophil
FcGammaRIIa?
Low affinity for IgG
Macrophages neutrophil
Phagocytosis
FcGammaRIIb?
Low affinity for IgG
B lymphocytes
Ab regulation
FcGammaRIIIA?
Low affinity for IgG
Only recognises Ab/Ag complexes - ADCC cannot be triggered by free Ig
NK cells, macrophage
ADCC
Signal v strong, one is enough to trigger
FcgammaRIIIb?
GPI linked
Low affinity for IgG
Neutrophils
Phagocytosis
Which antibody receptor on NK cells mediates ADCC?
FCgammaRIIIa
What does the C3b receptor recognise? What does it do?
IgM
Activates complement
Binding delivers complexes to the liver and spleen for removal by macrophages
How are helminths targeted?
IgE binds, recognised by FCepsilonRI (high affinity for IgE), triggers eosinophil to release granules containing proteins toxic to helminths
What are the effector functions of Ab?
- Opsonisation
- ADCC (virally infected cells, and via eosinophils for helminths)
- Mobilisation of inflammatory mediators
- Antibody transport
- Antibody feedback to regulate responses
FCepsilonRI
On eosinophils for IgE helminth ADCC
On mast cells and basophils, cross linked to cause degranulation and release of inflammatory mediators
Also triggered during allergic reactions when allergens bind IgE on mast cells
Which receptors are on mast cells and basophils?
FcepsilonRI and FcgammaRIII
Which Ig protect the mucosal surfaces from infection?
IgA and to a lesser extent IgM
How is IgA transported across epithelia?
Receptor recognises J chain region and transports it across.
J chain is the disulphide link region of IgM and IgA
How is the baby protected?
IgA in milk,
IgG that had been transported across the placenta