179 terms

immunology prelim 2

cellular immunity
T cell activities
humoral immunity
activities of antibodies
Plasma cells
-make antibodies
-sessile in the BM or medulla of lymph node (IgM)
-they are the most important part of B cell development
-the most immature blood cell that is considered a plasma cell instead of a B cell
-migrates from LN to BM, but can be diverted to sites of inflammation where it will release antibodies
Where does B cell activation take place?
Sec. lymphoid organs
Three signals for B cells
1. BCR and co-receptor complex bind antigens.
2. Co-stimulatory receptor is CD40
3. Cytokines
Cross linking surface Ig
-Signal communicated to interior by Ig-alpha, Ig-Beta, which each contain two ITAMs
-Src kinases or protein tyrosine kinases are activated by the binding and phosphorylate the chains at ITAMs
-Tyrosine kinase Syk binds Ig-beta that allows assembly of large signaling complex
B cell co-repceptor includes
-CD19 (complement receptor)
-CD81 (TAPA-1)
Co-receptors purpose
-enhances activation
CR2 or CD21
-complement receptor 2
-in complement process, C3b fragments on pathogen
-C3b is the ligand for the complement CR1 receptor on B cells which facilitates its cleavage by iC3b and C3d
-CR1, in doing this, increases B co-receptors on pathogen
-CR2 binds C3d, which brings the cell closer to pathogen
-after CR2 binds, brings CD19 close to tyrosine kinase Lyn, which phosphorylates it
-intracellular signal begins
Conjugation of C3d
Improves antibody responses by a lot
What are signals 2 and 3 of B cell activation*
-B cell serves as APC to activated T cell
-CD40 = signal 2
-cytokines = signal 3
*to activate T cell or to an already activated T cell?
How long do B and T cells remain associated?
10 min - 1 hr
B and T cells recognize the same antigenic site. T/F
Not usually - B cells will present many epitopes to T cells
Where does B cell develop?
Bone marrow, blood and sec. lymphoid tissue, lymphoid follicles, antigen
Bone marrow
Unrestricted repertoire of immature B cells. Tolerance induction
Blood and sec. lymphoid tissue
Self-tolerant mature B cels and anergized B cells. Additional tolerance induction -> then enter lymphoid follicles for antigen activation
Traffic pattern naïve B cells in LN
-CCL21 and 19 attract through HEV into LN
-attract to primary follicle where stimulated by dendritic cells and cytokines
Where do B cells circulate through?
Lymph, blood, sec. lymphoid tissue
Two pathways determine how develop:
-B cells move to medullary cords to become IgM
-B cells may more to germinal centers to become other
Important events in germinal center
-Clonal expansion
-Class switching
-Somatic hypermutation
-Differentiation of memory cells or plasma cells
Clonal expansion
-In dark zone
-B cells become known as centroblasts
-Clonally expand
FDC's with antigen
-One's that fix complement more immunogenic and stronger B cell stimulation
Immune complex coated bodies - have antigen all over surface for B cell binding
Somatic hypermutation
-During rapid proliferation
-CDR1, 2, 3 of V domain are hotspots
-High rate of mutation 10^-3 base pair/division
-Involves AID
-Activation indued cytidine deaminase (AID)
-The attraction between an antigen and an antibody
-Improves with time
-# mutations on heavy and light chain increases
Class switching
-In light zone under influence of T cells and specific cytokines
-Recombination of constant genes in heavy chain locus
Switch sites
-Sites targeted by AID
-Upstream of each CH except C delta
No switch with IgD
-No switch b/ no switch region upstream of C delta
What is class switch driven by?
-T cell cytokines
IgG1, IgE
Augments IgA production
IgG3, IgG2a
IgG2b, IgA
Plasma cells
-No surface Ig
-2000 ab/second
-Live for yrs. in BM
-400,000 in BM
-Continuous exposure to CD40L inhibits differentiation to plasma
-IL-10 promotes it
B cell vs. Plasma cell
-B cell have surface Ig, MHC and can go through processes in germinal center
-Plasma cells just secrete
Leads to plasma cell
Leads to memory cells
Memory cells
-Recirculate and live long
-High affinity receptors
-More likely than naïve cells to differentiate into plasma cells for homeostatic reasons
-Crucial to vaccination's effects
-Blood serum containing polyclonal antibodies
Complement system
-Bordet discovered antiserum could lyse bacteria
-Adding normal serum to antiserum complemented effects
-Heat response
Activation of complement system
Involves a series of proteolytic cleavages that yields products that can serve as opsonins, chemotactic factors, cellular activators, and lytic agents
-Both innate and adaptive immunity
-Dangerous and highly regulated
Complement can lead to macular degeneration
All complement things involve
C3 cleaved to C3a and C3b and C3b binding to surface of pathogen
-Opsonizes particles for engulfment by macrophages, which have receptors for it
-Chemotactic for neutrophils and macrophages
Cleavage of C3 exposes:
-Thioester bond
-Which can be soluble to H20 or bound to pathogen through R-OH or R-NH2
-After made in liver, bond available in plasma for pathogen
-Process whereby pathogen is marked for ingestion and destruction by a phagocyte
-CR1 on macrophage recognizes C3b on pathogen - endocytosis, makes vesicle, fuses with lysosome to form phagolysosome
Alternative pathway
-Pathogen surface creates local environment conducive to activate complement
Lectin pathway
-Mannose-binding lectin binds to pathogen surface to activate complement
Classical pathway
-C-reactive proteins or antibody binds to specific antigen on pathogen surface (adaptive immunity driving innate)
Alternative pathway steps
-C3 bound to H20 spontaneously in plasma to become iC3
-binds factor B
-protease factor D cleaves B to Bb, with Ba released
-Now, iC3Bb
-Intact C3 binds iC3Bb which cleaves it to form C3a, C3b
Then once C3b is bound...
-Factor B binds, D cleaves to make C3bBb, C3 makes many more C3b's on pathogen surface
Limits on complement activation on surface of animal cells
-Inhibitory proteins H and I
-H binds to sialic acid and makes sure that if C3b deposited, that it cleaved by I to make iC3b
-Bacteria don't have sialic acid so no limits
Factor I
-Limits animal cell C3b
-Also can cleave iC3b to C3d, which is recognized by CR2 on FDC and B lymphocytes
Antibodys' effects on Activating complement
-IgM low affinity, very good with complement
-IgG3 also very good
-IgG1 and 1 chosen in therapeutic antibody design depends on desired outcome
-binds C-reactive protein which binds phosphocholine on pathogen
-or binds IgM
Specific IgM conformation exposes C1q binding sites - staple conformation
Once C3b is bound will generate more convertase via alt. pathway
C4b assoc. with C2a
-becomes a convertase for C3
Process of classical
1. C1 binds ab/ag complex
2. Deposition of C4b by C1
3. Deposition of C3b by C4b2a
4. Deposition of C3b by C3bBb
Pentameric IgM vs. IgG
C1 binds single staple
C1q binds multiple IgG
Mannose binding lectin
-MBL and its associated serene proteases mimics C1q
-Has 2 MASP1 and 2
The process of lectin binding
-Once MBL binds pathogen, activates MASP2 which cleaves C4 to C4a/b; also C2 to C2a/b
-C4b binds to microbial surface
-C2a binds surface of C4b forming classical C3 convertase
-Binds C3 and forms C3b
Terminal pathway
-C3b2Bb can cleave C5 to C5b, which leads to terminal pathway
-Binds C6, 7, 8, 9 on surface
-very important chemotactic factor
*** what does that diagram mean???
-C5 activation a cause
Acute phase response
-Triggered in the liver by cytokines (TNF-a, IL-1B, and IL6) generated in innate response
-Generates additional mediators of inflammation to promote destruction of infectious agents
-Can be prolonged if infection not cleared
Effector cells
Macrophages and mast cells
Pro-inflamatory cytokines
-Released by macrophages
-IL-6, TNG-a, IL-1B, CXCL8, IL-12
-What should we know about the pro-inflammatory responses?
IL-1, 6/ TNF-a
Act on liver, bone marrow, hypothalamus, fat/muscle --> activation of complement opsonization, phagocytosis, decreased viral and bacterial replication
-Acts on hepatocytes to induce acute phase response
-then, C-reactive protein binds phosphocholine on bacterial surfaces, acting as an opsonin and as a complement activator
-Mannose-binding lectin binds to carbs on bacterial surfaces -> complement activator
There are mechanical, anti-microbial and chemical defenses
Pathogens vary in associations with hosts...
Extracellular, intracellular
-Caused by direct and indirect effects of pathogens: a great deal of what we see as disease during infections is the result of the immune response
Signs of inflammation
-Swelling, redness, heat, pain, loss of function
-Positively charged peptides that associate with negatively charged urfaces of bacteria and then create pores in the bacteria to kill it
-Attack bacteria, viruses, and fungi
-35 to 40 amino acids
-Expressed mainly by neutrophils and paneth cells
-Expressed by a large range of cells
Paneth cells
-Located at the crypts of the small intestine
-HD5, HD6
Myeloid cells
-Cells that are induced - require a cellular response to a threat or pathogen
Recognition of pathogens
-outcomes are phagocytosis and cytokine production
-Family of signaling receptors which is specific for a different set of microbial products
-Important in pathogen recognition
-Activate innate cells and indirectly influence adaptive immunity
Know structure of TLR
-N and C
-Leucine-rich repeats
-Pathogen recognition domain
-TIR domain
-Transmembrane polypeptide with a TLR
What to know from second slide on 10?
Bacteria outer surface
Lippolysarccharide, then outer membrane, then peptidoglycan, then inner membrane
-Receptors and plasma proteins that recognize carbohydrates
Scavenger receptor
-Phagocytic receptor of macrophages that is not a lectin
Important in body's defense against gram negative bacteria
-recognize bacterial lipopolysaccharide with MD2, LPS and CD14 at cell surface`
-After TLR with gram negative bacteria
-Transcription factor for inflammatory cytokines
The process
-TLR4, MD2, CD14, LPS on macrophage surface
-MyD88 binds TLR4 and activates IRAK4 to phosphorylate TRAF6 to phosphorylate IKK
-IKK phosphorylates IkB leading to release of NFkB
-NFkB goes to nucleus to make inflammatory cytokines
Alternative pathway
-After detects ligands, TLR4 or TLR3, bind TRIF and TRAM
-Phosphorylate TRAF3
-Kinase cascade
-Phosphorylate IRF3, which directs transcription ---IFN a, b
-Local inflammatory response that helps contain infections
-Also systemic effects
-Local only - helps attract neutrophils to site
IL-1, IL-6, TNFa
-All critical role in inducing acute phase response
-All systemic effects
-Local only - Activates NK cells
-Systemic only - acute phase response; fever
-Increase release of plasma proteins into tissue
-Increased phagocyte and lymphocyte migration into tissue through having endothelial cells increase expression of adhesion molecules
-Increased platelet adhesion to blood vessel wall
Septic shock ** explain
-When systemic infection with gram negative bacteria
-TNF-a into bloodstream
-Decreased blood volume, hypopoteinemia, neutropenia, decreased blood volume causes collapse of vessels
-Dissemnated intravascular coagulation leads to wasting and multiple organ failure
1. Bacterium becomes attached to membrane evagination called pseudopodia
2. Ingested forming phagosome
3. Fuses with lysosome
4. Digested and digestion products released from the cell
Where are TLRs?
-Dendritic cells
-TLR engagement activates DC to upregulate CCR7 which binds CCL21 in sec. lymph tissue to move to lymph node
-Also upregulates MHC and B7 to activate DC
What happens when injury in epithelia?
-Tissue damage causes release of vasoactivate and chemotactic factors to increase blood flow and permeability
-Allows cells and fluid to go there
Bradykinin, Fibrin degradation, Plamin and complement activation
Mast cells
-Important initiators of adaptive response
-Reside near blood vessels in connective tissue; produce same chemo/cytokine
-Macrophages with granules
-Degranulate in response to IgE bound to surface receptors
-have TLRs and receptors for C3a, C5a
-Activated by bacteria and compement
Mast cells
-Break down membrane phospholipids to generate vasoactive and chemo-attractive molecules
-From mast cells breaking down phospholipids
-Can cause clotting
Arachidonic acid
-From mast cells breaking down phospholipids
-Vascular permeability and neutrophil chemotaxis
-Gets in the way of the cyclooxygenase pathways
A chemoattractant for neutrophils
-Made by macrophages
-High number in blood and large reserve in BM
-roll stop drop mechanism
How do neutrophils work?
-Bacterium is phagocytosed by neutrophil
-Fuses with azurophilic (lysozyme, defensins, myeloperoxidase, and proteases) and specific granules (lysozyme, NADPH)
-pH rises, antimicrobial response activated
-pH drops and allows lysosome to bind to phagosome and completely destroy bacteria
-Neutrophil dies and phagocytosed by macrophage
Respiratory burst
-Neutrophils have an enzymatic pathway toxic to micro-organisms
-WIth Superoxide and H2O2
-Key feature of neutrophils
-Infected the ear
-Leishmania red and green neutrophils
-Neutrophils aren't necessarily directed at micro-organisms
Virus infection
-Cell mediated immunity is necessary for clearance of a primary infection, antibodies are crucial to preventing secondary infections
-IFN-gamma, CTLs, NK, macrophage
Influenza has an antigenic hemaglutinin
-Encapsules genome of virus
-For influenza, single stranded RNA (ssRNA)
Innate defense against viruses
-TLRs that recognize ssRNA which will initiate innate response to the virus
-TLR7, 8
TLR 7 and 8
-In endosome can bind ssRNA -> signal that leads to production of IFN-a, b
If virus infects via endosome, or endocytosed by DC, viral RNA can bind TLRs
Interferon and viruses
-Viruses bind surface of cells, release nucleic acids bound by TLR in cell -> IFN responses and transcription
-IFN-B released by cell and binds another cell to prevent viral infection of that cell
-also IFN B bind same cell to prompt IFN A
-paracrine and autocrine responses
-cause cell to stop synthesizing protein
-inhibits viral replication
Second slide of 5?
Type I interferons
-alpha and beta
-three functions are induce resistance to viral replication by activating cellular genes that destroy viral mRNA and inhibit the translation of viral proteins
-Increase expression of ligands for NK cell receptors on virus infected cels
-Active NK cells to kill virus infected cells
NK cells
-Lymphocytes of innate immunity that specialize in defense against viral infections
-Lymphoid progenitor
-"large granular lymphocytes"
-produce IFN-gamma when stimulated by IL-12 and TNF-alpha
-cytotoxic which is promoted by exposure to IFNa/B or IL-12
NK cell receptors
-most are extracellular ligand binding regions of Ig domains or lectin like domains
Activating NK receptors
-Short cytoplasmic tails
-Changed amino acid residues
Inhibitory NK receptors
-Long cytoplasmic tails that contain short amino acid sequence called immuno-receptor tyrosine based inhibitory motif ITIM
-binds protein pho sphatases that act to inhibit
NK cells distinguish cells
-NKG2D- an activating receptor present on all human NK cells
-ligands for NKG2D are MIC-A and MIC-B, which are only expressed by viral or traumatic cells
-healthy cells only have interaction b/w inhibitory receptor and ligand whereas viral cells have NKG2D interact with MIC to activate and over-rule inhibitory response
Time until virus gone
1. Proudciton of IFN a, B, TNFa, and IL12
2. NK cells
3. T cell killing
Movement of effector cells
-Dendritic cells pick up bacterial antigens in skin and move to draining lymphatic vessel and settle in T cell areas of LN
Antigen-specific T cell movement
-Trapped in LN where activated briefly then enter blood and diverted to sites of infection by altered endothelial cell surface receptors
Cell-surface molecules and T cells
-VLA-4 binds VCAM on endothelial T cells in blood vessels at sites of infection to extravascate into sites of inflammation
-T cells don't have L-selectin - can't cross HEV - rather enter LN via afferent lymphatics
Broadly defined effector functions
-Effector cells do not need co-stimulatory receptors to engage their target cells
CD8+ T cells activation/function
-On professional APC
-Proliterate by IL-2
-Targets any somatic cell
-Cytotxic T cell
-Recognizes virus-infected cell
-Programs cell to die and moves to another cell
Proteins in granules of cytotoxic T cells
-Perforin, granzymes, granulysin
-Aids in delivering contents of granules in cytoplasm of target cell
-Serine proteases
-Activates apoptosis once in cytoplasm of target cell
-Antimicrobial and induces apoptosis
CTL function
-Collision and non-specific adhesion doesn't work
-Engagement of the TCR allows polarization of T cell and release of lytic granules
What happens when a naïve CD8 binds class I plus non-professional APC?
CD8+ cytokines
-IFN-gamma, LTa, TNFa
CD4+ activation
-Activated by TCR and C4 binding
-CD28 with B7
-IL-6, IL-4, IL-12, TGF-B cytokines from APC
-Cytokine signal directs differentiation
-Acts on lymphocytes, enhancing responses
-Acts on Naive T cells and makes them Th1
Different cytokine differentiation on T cell
-TGF-B then FoxP3 then Treg
-TFG-B, IL-6 TH17 cells
-IL-12, IFN-gamma then Tbet and IL2 then Th1
-IL-4 then GATA3 IL4 IL5 then Th2
IL2 and IL4
Important for T cell growth and development
IFN gamma, lymphotoxin alpha, IL10
Inhibits or kills T cell
T helper 17
-TGF-B and IL-6
-Then RORgammaT, IL-6, 17
-Then Th17
DC produce IL-6
-At early infection
-Naive CD4 cells express ROR T and become Th17
-released at sites of infection
-stimulates epithelial cells and fibroblast to produce chemokines that recruit neutrophils, as well as CSFs that stimulate neutrophil production.
-This delivers more neutrophils to sites of infection.
-Suppressor cells
-FoxP3 interferes with Th1 and Th2
-Produce TGF-B/IL10
-IL-10 inhibit activation of macrophages
-TGF-B inhibits cell growth
DC make TGF B and IL-10
-In these conditions, Tregs form b/c T cells have FoxP3
-Inhibits T cell and macrophage growth but promotes survival
-Switch factor for IgA
-Inhibits Th1, cytokine release by macrophages, upregulates class 2 on B cells, influences B cell differentiation, produced by Th2 cells
-Associated with Tregs
IL-12 and IFN-gamma
-Lead to transcription factor T-bet
CD4 Th1 function
-activate macrophage, help for B cells for antibody production
-Targets vesicular and extracellular microbes
What stimulates T cells to become Th1
-Viruses and bacteria induce DC to do IL-12 and NK cells to produce IFN-gamma
-Important for TLRs
-Also for development of IL-12 IFN-gamma
Effector function of Th1
-Activate macrophage by CD40 ligand on T cell which makes macrophage reflective to IFN-gamma which Th1 produces
-Macrophage activated in antigen specific manner
Activated macrophage has:
-Phagosome/Lysosome fusion, induction of respiratory burst, inducible nitric oxide synthase
Respiratory burst in macrophages
-Activated NADPH converts O2 to O2-
-Then converted to H2O2
-Then to radicals and ions
-These are toxic to microbes
Antimicrobial mech. of phag.
-Toxic nitrogen oxides, acid, anti-microbial peptides, enzymes
Th2 activation
-Parasitic worms cause IL-4 secreted by NK T cells
-Th2 cells can drive alternate activation of macrophages
Cross regulation of T cell subtypes
-Treg inhibits Th1 2
-Th1 inhibits Th2 vice versa
-Polarization - only one cell a focus when chronic illness
-live in vesicles
-multiple ways of attacking
-Grows in body, initiated by bite of sand fly
Mice with leishmania
-Those with Anti-IL-4 can make Th1
-Th1 clears intracellular parasite while Th2 does not
What drives antibody class switching?
-T cell cytokines
-Th2 -> IL-4, IL-5 -> IgG1, IgE, augments IgA
-Th1->IFN-gamma ->IgG3, IgG2a
-Treg-> TGF-B-> IgG2b, IgA
Functions of antibody isotopes
1. Fab dependent function
2. Fc dependent functions
Fab dependent functions
-Virus and toxin neutralization and inhibition of bacterial inhibition by IgM, IgG, IgA
Fc dependent functions
-Complement activation
-FcR binding - opsoniation
-IgE activate mast cell
-Antibody dependent cell mediated cytotoxicity
Two classes of IgA in humans, LIttle IgE in the blood b/c associated with mast cells
What is the dominant class in humans?
-with important half life
Different IgG antibodies differ with the hinge region
best at activating complement
-response to allergens
-can become functionally monovalent through exchange mechanism
Antibodies are flexible