Robbins Ch 6 Immunity
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Explain the binding of LPS to TLRs and its downstream effects.
LPS binds to LPS-BP and binds to CD14, BP dissociates, CD14-LPS binds to TLR4 and its accessory protein MR2, the cytoplasmic TIR domain of the TLR recruits MyD88 which activates signaling molecule TRAF6 which activate NF-kb
Name the ligands and sources for TLR2.
- LP (bact)
- Peptidoglycans (G+ bact)
- LPS (lepto)
- Zymosan (fungi)
- GPI anchor (trypanosomes)
- Lipoarabinomanan (mycobact)
- Phosphatidyl dimanoside (mycobact)
Name the ligands and sources for TLR3.
DS DNA (viruses)
Name the ligands and sources for TLR4
- LPS (G- bact)
- HSF00 (Chlamydia)
Name the ligands and sources for TLR5
Name the ligands and sources for TLR6
CpG DNA (bact, protozoa)
What does abTCR recognize?
Peptides displayed on MHC
Describe the structure of the TCR complex.
5 parts: TCRa and b + 2z and 3 CD3 � g, d, e
What does the gdTCR recognize?
Peptides lipids and small molecules not associated with MHC.
What do Tcells need for activation?
- 2 signals:
- 1) TCR binds to MHC bound Ag along with accessory mol (ex. CD4 � MHCII, CD8 � MHCI)
- 2) Co-stim molecules � CD80 or 86 (B7-1 and 2) on APC to CD28 on Tcell
What happens if co-stimulation of Tcell (via CD28-CD80/86) does not occur?
What cytokines do TH1 and TH2 secrete? What are there functions
- TH1: IL2 and IFNg � fxn: delayed hypersensitivity, mac activation, IFNg stim prod of opsonizing/complement fixing abi
- TH2: IL4, IL5 and IL13 � fxn synthesis of other classes of abi � IgE esp and activation of eos
- NOTE: CD8 T cells are cytotoxic but can secrete TH1 type cytokines
Describe the structure of the BCR complex:
Heavy and light chains of Ig plus CD79a-b heterodimer (NB for signal transduction)
List other molecules NB for B-cell function:
FC, CD21 (complement receptor 2), CD40
How do Tcells help Bcell activation?
CD4 T cells express CD40L � binds to CD40 on Bcell ? secrete IgG, IgA, IgE
How are macrophages activated?
IFNg by CD4 Tcells
Macs phagocytize microbes opsonized by which molecules?
IgG or C3b
Name the two types of DCs and some of their features.
- Interdigitating: epithelia, interstium of tissues, have lots of MHCII and co-stim mol B7-1 and 2 (so activate T cells) and receptors for same chemokines as na�ve T cells so move with them
- Follicular: germ centers of LN, spleen, Fc for IgG and C3b receptors so trap opsonized Ag then present to B cells and pick best ones!
What is the difference between NK cells and NK-T cells?
The latter have TCR as well as NK receptors, NK cells have no TCR or surface Ig
Name some of the NK markers.
CD56, CD16 (Fc for IgG)
Describe the activating and inhibiting effects on NK cells.
- NK cells have activating receptors: ex. NKG2D � recognize stress induced proteins, viral proteins etc.
- Also have inhibiting receptors ex. KIR, CD94-NKG2A,B - bind to self MHC I on normal cells to inhibit
- If cells viral inf or mal transformed then decrease MHCI and incr. expr of activating receptors ? killing
What cytokines do NK cells produce?
IFNg (activate macs and promotes diff of TH1 cells), TNF and GM-CSF
What cytokines regulate NK cells?
IL2 and IL15 stim prol, IL12 activates killing and secretion of IFNg
Which cytokines mediate innate immunity?
Innate: IL1, TNF, IL6 (IL12 and IFNg � both innate and adaptive)
Which cytokines protect against viral infection?
Which cytokines regulate lymph growth, activation and differentiation?
IL2 (T cell GF), IL4 (TH2), IL12 (TH1), IL15 (NK), TGFb, IL10 � latter 2 downregulate immune response
Which cytokines activate inflammatory cells?
IFNg (mac), IL5 (eos), TNF and lymphotoxin (neuts and endo)
Which cytokines affect leuk movement (ie. chemokines)?
C-C (made by T cells) or C-X-C (made by macs and endo)
Which cytokines stimulate hematopoiesis?
G and GM-CSF, c-kit, CD117 � more� not listed
Describe differences between MHCI and II.
- MHC I present on all cells, present endogenous proteins ex. viral antigens, cytosolic proteins are processed in proteosomes, transported to ER, binds to MHCI, transported and presented at surface to CD8 T cell � Ag binds to TCR
- MHC II only on APCs (macs, DC, some Bcells), present exogenous proteins to CD4 T cells, proteins are first processed in lysosomes or endosomes � note: can be induced on fibroblast and endo cells by IFNg
Describe Type I (immediate) hypersensitivity reaction.
- Ex. Anaphylaxis, allergies, atopy
- Ag presented by DC to TH2 cell
- TH2 secretes: IL4 (prol of TH2, activate na�ve B to IgE prod), IL5 (activates eos) and IL13 (? IgE, mucus)
- TH2 and epi produce chemokines to attract more TH2
- Mast cells and basos have Fc receptors for IgE, after X-inking of IgE, mast cells release granule contents
- with mediators
- Primary mediators: histamine (sm mm contraction, incr. vas perm, incr gland secretion of nasal, bronch and gastric glands), enzymes � acid hydrolases and neutral proteases, heparin and chondroitin sulfate (package and store other mediators).
- Secondary mediators:
- Lipid mediatiors: LT and PG via action of PLA2 on mast cell membranes (aa pathways), LTC4/D4 � sm mm cont and vasoactive, chemotactic for neuts, eos, monos, PGD2 � bronchospasm, PAF (triggered by PLA2 � plt ag, histamine release, bronchospasm, vas perm, vasodil, chemotactic for eos and neuts
- Cytokines: mast cells release: TNF, IL1, IL3, IL4, IL5, IL6, GM-CSF, MIP 1a and 1b (both chemokines)
- Epis can produce IL6, IL8 and GM-CSF
- Eos survival incr. by IL5, IL3 and GM-CSF (TH2 and MCs)
- Eos can also produce PAF and LTC4
- NOTE: Reaction can also be stim by C5a, C3a, IL8 (from macs), drugs (codein/morphine), mellitin (bee toxin), physical stimuli
What mediators result in vasodilation?
What mediators result in increase vascular permeability?
- LT C4, D4, E4
- Neutral proteases
- PG D2
What mediators result in smooth mm contraction?
- LT C4, D4, E4
What mediators result in cellular infiltration?
- LT B4
- Eos and neut chemotactic factors
Describe Type II (Abi-mediated) hypersensitivity.
- ex. IMHA, transfusion rxn, NI, drug rxn
- 3 different mechanisms:
- 1. Opsonization, complement and FC mediated phagocytosis
- IgG or M dep on membrane � complement activation � C3b and C4b bind cell surface and macs phag d/t complement receptors on surface, macs also have FC receptors so can phag cells opsonized by IgG
- complement fixation also leads to killing with MAC
- This can also occur via NK cell, mono, neut or eos (ADCC) � usually IgG
- 2. Complement and FC receptor mediated inflammation
- Abi deposited on BM and ECM � activate complement C5a (some 4a, 3a) � recruit neuts and monos which bind to abi via FC receptors � activate and release mediators � damage to tissues
- 3. Antibody mediated cellular dysfunction: abi bind to cell-surface receptors interfering with fxn ex. myasthenia gravis or pemphigus vulgaris (abi vs epi jxns � vesicle formation)
Describe type III (immune complex mediated) hypersensitivity.
- ex. SLE, glomerulonephritis, serum sickness, arthus reaction � rxns can be generalized or localized
- Ag combines with Abi in circulation � deposit in vessel walls
- See in three phases: 1. formation of complex in circulation, 2. deposition in tisues 3. inflammation
- Most pathogenic complexes are: small with excess Ag � phagocytized less readily
- Inflammation is caused by: 1. activation of complement and/or 2. activation of neuts/macs via FC rec
- Complement activation results in recruitment of PMN and monos (C5a) and release of anaphylaxatoxins (C3a and 5a) � increase vascu perm
- When leuk get there they are activated via C3b and Fc receptors � proinflam mediators � PGs, vasodilator peptides, chemotactics, lysosomal enz, ROS
- Complexes also ag plts and activate FXII
- IgG and IgM fix complement and IgG binds Fc
Name disease examples of type III
- SLE, vs DNA, nucleoproteins --- nephritis, arthritis, vasculitis
- Blue eye, vs canine adenovirus --- ant uveitis
- EIA vs viral antigen --- anemia, Tpenia
- Arthus rxn vs foreign proteins --- cutaneous vasculitis
- COPD vs fungal spores, dust ---- bronchiolitis
- Aleutian mink dz ---- viral ag --- glomerulonephritis
Describe type IV (delayed) hypersensitivity.
- ex. DM, MS, RA, TB, contact derm, Johne�s dz, allograft rejection, equine recurrent uveitis
- Initiated by Ag activated T lymphs � delayed type rxn by CD4
- APC presents Ag on MHCII to na�ve CD4 cell � differentiated to Th1 cell --- secretes IFNg
- Macs/APC secrete IL12 NB for diff into Th1 cell � induce IFNg prod by the Th1 cell
- IFNg that is secreted activates macs � more effective killing, more MHCII, PDGF prod (fibroblast prolif, collagen syn), secreteTNF, IL1 and chemokines and more IL12 (amplifies)
- IL2 also secreted by Th1 � autocrine to incr T cell prol and paracrine
- TNF and lymphotoxin � effects on endo cells: prostacycline (incr bld flow), exp of P and E selectins � attach passing lymphs and monos and induces secretion of IL8 � extravasation of lymphs and monos to rxn
Describe T cell mediated cytotoxicity.
- Sensitized CD8 cells via perforins and granzymes within preformed vescicles in the CTL, perforins perforate membrane and granzymes initiate apoptosis
- Also express FASL which binds FAS and mediates Apoptosis
Name and describe the three mechanisms of peripheral tolerance.
- 1. Anergy � T cell activation needs 2 signals including the costim signal � self tissue cells have no costim mol
- 2. Suppression by Treg � CD4 cells express CD25 � mech ? but involves IL10 and TGFb, need transcription factor Foxp3 for Treg cell dev and fxn
- 3. Clonal deletion by activation induced cell death � some T cell express FasL, thought that self T cell keep getting stimulated till they die by Fas ligand induced apoptosis or possibly by expressing BIM (pro-apoptotic molecule)
- NOTE: if self-reactive T cells are stim by exposure to an infectiou agent � they can then prol and get autoimmunity.
What is amyloid?
Proteinaceous substance made up of non-branching fibrils with cross beta pleated sheet conformation � 95% is fibril proteins the rest is P component and other glycoproteins
Name 3 forms of amyloid.
- AL � from plasma cells, Ig light chains � associated with B monoclonal dz
- AA � non- Ig produced in liver � fibrils derived from SAA, circulated in association with HDL3 lipoproteins
- A? - Alzheimers
List and describe the types of amyloidosis.
- 1ry: associated with monoclonal gammopathies � ex. MM
- 2ry: associated with chronic inflammation � SAA synthesized in response to IL6 and IL1
- Hereditary: heterogenous group of dzs
- Endocrine amyloid: medullary carcinoma of thyroid, islet tumors of pancreas, pheo, carcinomas of stomach --- amyloid derived from polypeptide hormones or unique proteins produced by the tumor
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