浙江大学医学免疫学经典课件免疫9、13B细胞文档资料.ppt

The discovery of B cell immunity1954 - Bruce Glick, Ohio State UniversityStudies on the function of the bursa of Fabricius, a lymphoid organ in the cloacal region of the chickenBursa was later found to be the organ in which antibody producing cells developed – antibody producing cells were thereafter called B cellsMammals do not have a bursa of FabriciusTransfer marked foetalliver cellsOrigin of B cells and organ of B cellmaturationNo MatureB cellsAfter birth, development continues in the bone marrowNormal bone marrowDefective bone marrowMature markedB cellsin peripheryB cell development starts in the foetal liverB cell development in the bone marrowBRegulates construction of an antigen receptorBone Marrow provides aMATURATION & DIFFERENTIATION MICROENVIRONMENTfor B cell developmentEnsures each cell has only one specificityBChecks and disposes of self-reactive B cellsBExports useful cells to the peripheryBProvides a site for antibody productionBSecretedFactors - CYTOKINES2. Secretion of cytokines by stromal cellsBBone marrow stromal cells nurture developing B cellsTypes of cytokines and cell-cell contacts needed at each stage of differentiation are differentStromal cell1. Specific cell-cell contacts between stromal cells and developing B cellsCell-cell contactBone marrow stromal cellMaturing B cellsBBStromal cellB lineage commitmentHSC (hematopoietic stem cell) MPP ( (淋巴系髓系多能前体细胞淋巴系髓系多能前体细胞) ) ELP (earliest lymphocyte progenitor) ETP (early T-lineage progenitor)CLP (common lymphoid progenitor) HSCHSCHSCHSCDevelopment and migration of B cells (An overview)Stages of differentiation in the bone marrow aredefined by Ig gene rearrangementB CELL STAGEIgH GENECONFIGURATIONStem cellEarly pro-BLate pro-BLarge pre-BGermlineDH to JHVH to DHJHVHDHJHPre-B cellreceptorexpressedIg light chain gene has not yet rearrangedB cell receptorTransiently expressed when VHDHJH CHm is productively rearrangedIga & Igb signaltransductionmoleculesCHmHeavy chainVHDHJHLight chainVLJLCLVpreBl5Pre-B cell development is coupled with rearrangement of heavy-chain B cell development is coupled with rearrangement of heavy-chain B cell development is coupled with rearrangement of heavy-chain B cell development is coupled with rearrangement of heavy-chain B cell development is coupled with rearrangement of heavy-chain B cell development is coupled with rearrangement of heavy-chainSplicing of IgM and IgD RNACm1Cm2Cm3Cm4Cd1Cd2Cd3pA1VDJCm1Cm2Cm3Cm4Cd1Cd2Cd3VDJAAA RNA cleaved and polyadenylated at pA2VDJ CmIgM mRNAVDJ CdIgD mRNAC1C3CdCmVDJCm1Cm2Cm3Cm4Cd1Cd2Cd3DNApA1pA2VDJTwo types of mRNA can be made simultaneously in the cell by differential usage of alternative polyadenylation sites and splicing of the RNARNA cleaved and polyadenylated at pA1AAA B cell development is coupled with rearrangement of heavy-chain6000 heavy chains combined with 320 light chains 1.9X106 Abs Ligation of the pre-B cell receptor1. Ensures only one specificty ofAb expressed per cellLargePre-BStromal cellUnconfirmed ligand of pre-B cell receptor2. Triggers entry into cell cycleALLELIC EXCLUSIONExpression of a gene on one chromosome prevents expression of the allele on the second chromosome1. Suppresses further H chain rearrangement2. Expands only the pre-Bcells with in frame VHDHJH joinsEvidence for allelic exclusionAllotypes can be identified by staining B cell surface Ig with antibodiesa/ab/ba/bYBbYBaYBbYYBabYBaANDALLOTYPE- polymorphism in the C region of Ig – one allotype inherited from each parentSuppression of H chain rearrangement by pre-B cell receptor prevents expression of two specificities of antibody per cell(Refer back to Dreyer & Bennet hypothesis in Molecular Genetics of Immunoglobulins lecture topic)YYYYSuppression of H chain gene rearrangementensures only one specificity of Ab expressed per cell.Allelic exclusion prevents unwanted responsesBSelf antigenexpressed bye.g. brain cellsS. aureusYYYYYBS. aureusYYYYYYYAntiS. aureusAntibodiesYYYYYYAntibrainAbsOne Ag receptor per cellIF there were two Ag receptors per cellYYYYYYYAntiS. aureusAntibodiesPrevents induction of unwanted responses by pathogensAllelic exclusion is needed for efficient clonal selectionAll daughter cells must express the same Ig specificityotherwise the efficiency of the response would be compromisedSuppression of H chain gene rearrangement helps prevent the emergence ofnew daughter specificities during proliferation after clonal selectionS. typhiAntibodyS. typhiAllelic exclusion is needed to prevent holes in the repertoire Exclusion of anti-brain B cells i.e. self toleranceYYB BOne specificity of Agreceptor per cellS. aureusAnti-brain IgANDanti-S. aureus IgYYYB BIF there were two specificitiesof Ag receptor per cellAnti-brain IgBBDeletionAnergyORanti S.aureus B cells will be excluded leaving a “hole in the repertoire”BUTYYYB B1. Suppresses further H chain rearrangementLigation of the pre-B cell receptor1. Ensures only one specificity ofAb expressed per cellLargePre-BStromal cellUnconfirmed ligand of pre-B cell receptor2. Triggers entry into cell cycle2. Expands only the pre-Bcells with in frame VHDHJH joinsLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BLargePre-BProliferationYImmatureB cellLight chain expressedIgM displayed on surfaceIgMLigation of the pre-B cell receptor triggers entry into the cell cycleLargepre-BMany large pre-B cells with identical pre-B receptorsLarge pre-BIntracellular VDJCH chainVL-JL rearrangesProliferation stopsPre-receptor not displayedSmall pre-BBYYYYBSmall pre-B cellNo antigen receptor at cell surfaceUnable to sense Ag environment!!May be self-reactive!!Immature B cellCell surface Ig expressedAble to sense Ag environmentCan now be checked for self-reactivityAcquisition of antigen specificity creates a needto check for recognition of self antigens1.Physical removal from the repertoireDELETION2.Paralysis of functionANERGY3.Alteration of specificityRECEPTOR EDITINGB cell self tolerance: clonal deletionImmature B cell recognisesMULTIVALENTself AgBClonal deletion byapoptosisY YBImmatureBBSmallpre-BSmall pre-B cellassembles IgYB cell self tolerance: anergyBYYYBAnergic B cellIgD normal IgM lowImmature B cell recognisessoluble self AgNo cross-linkingYYBImmatureBBSmallpre-BSmall pre-B cellassembles IgIgMIgDIgDIgDReceptor editingA rearrangement encoding a self specific receptor can be replacedVCD JVVVYBB!!Receptorrecognisesself antigen!!BApoptosisor anergyYBBEdited receptor now recognisesa different antigen and can berechecked for specificityCD JVVVVArrest developmentAnd reactivateRAG-1 and RAG-2YYYYYYMature B cellexported to theperipheryYYB cell self tolerance: export of self tolerant B cellsIgD and IgM normalIgMIgDIgDIgDIgDIgMIgMIgMImmature B cell doesn’t recognise anyself AgYYBImmatureBBSmallpre-BSmall pre-B cellassembles IgBB-cell surface markers1. BCR complex•BCR (mIg): VH, VL----Ag binding site mature B cells: mIgM and mIgD. Function: specifically recognizes antigen. •Ig /Ig  (CD79a/CD79b): heterodimer cytoplasmic domains contain ITAM. Function: transduce the signals that lead to B cell activation.Antigen receptor-mediated signal transduction in B cellsCD19/CD21/CD81complex CD21=CR2, C3dR, EB virus receptor CD19/CD21/CD81 interactions with complement associated with antigen play a role in antigen-induced B-cell activation.2. Co-receptorsThe role of the coreceptor in B cell activation(1)CD40 interacts with CD40L (Th cell) (2)CD80(B7.1), CD86(B7.2) Expressed on activated B cells and other APCs (3)ICAM-1 （（CD54）、LFA-1（CD11α/CD18)： mediate cell-cell interaction and co-stimulation3. Co-stimulatory molecules(1)CD20: function is unclear. It is suspected that it acts as a calcium channel in the cell membrane(2)CD22：Inhibitory receptor with ITIM motif(3)CD32 (FcRII)： Inhibitory receptor(4)Cytokine receptors(5)Complement Receptors(6)Toll-like receptors(7)MHC 4. Other receptors3. Subtype of B cells1.Conventional B cells (B-2 cells) 2.B-1 cells (expression of CD5)CD5Two B cell lineagesBB cell precursorBMature B cellB2 B cellsPlasma cellYYYYYYYYYPCIgGBYYYYYYYYYYYYYYYYYYYYIgM - no other isotypesBDistinct B cellprecursor??B1 B cells‘Primitive’ B cells found in pleura and peritoneumB-2 cells : conventional B cells Recirculating follicular B cells : circulate between LN follicles and bloodmIg: IgM, IgDProduce IgG after antigenic stimulation in the presence of T helper cells •B1 cells (CD5+): Many of the first B cells that appear during ontogeny express CD5, a marker originally found on T cells. (express mIgM, no mIgD). They respond well to TI-Ag and may also be involved in the Ag processing and presentation to T cells. Functions 1. produce anti-bacterial IgM the first line of defence against microorganisms; 2. produce polyreactive Ab clearance of denatured self components; 3. produce auto-Ab, thereby participating in the pathogenesis of some autoimmune diseases. Comparison of B-1 and B-2 B cell propertiesPropertyB-1 cellsB-2 cellsN regionsFewExtensiveV region repertoireRestrictedDiverseLocationPeritoneum/pleuraEverywhereRenewalSelf renewal in situBone marrowSpontaneous Ig productionHighLowIsotypesIgMIgM/G/A/D/ECarbohydrate specificityYesRarelyProtein specificityRarelyYesNeed T cell helpNoYesSomatic hypermutation of IgNoHighMemory developmentNoYesYes RarelyRarely YesNo YesCarbohydrate specificityProtein specificityNeed T cell helpSpecificity & requirement for T cell help suggests strikingly different typesof antigens are seen by B-1 and B-2 B cells4. Function of B cells1. Production of antibody Abs prevent microorganism from entry into cells and eliminate microorganisms by opsonization causing phagocytosis, complement activation and toxin neutralization.2. Ag presentation to T cells3. Immune regulation Secretion of cytokines (TNF, IFN, IL-12) →M, DC, NK, B cell. Co-stimulation of T cells→T cell proliferation.Y``Y``Immune effector mechanisms against extracellular pathogens & toxinsNEUTRALISATIONY``Toxin releaseblockedPreventstoxicityNEUTRALISING ANTIBODIESAdhesion tohost cells blockedPreventsinvasionBacteriumY``ToxinFc receptorbindingEffector mechanisms against extracellular pathogensOPSONISATIONOPSONISATIONPhagocytosisBacteria in extracellular spaceAb+Effector mechanisms against extracellular pathogensCOMPLEMENT ActivationBacteria in plasmaAb & COMPLEMENT+PhagocytosisbindingComplement &Fc receptorLysisOpsonisationADCCB cell-mediated humoral immune response•Humoral immunity is mediated by antibodies and is the arm of the adaptive immune response that functions to neutralize and eliminate extracellular microbes and microbial toxins.•It is more important than cellular immunity in defending against microbes with capsules rich in polysaccharides and lipids.•TD-Ag： T cell-dependent•TI-Ag： T cell-independentResponse to TD-Ag1) B cells recognize TD-Ag a. BCR directly recognizes B cell epitopes b. Ig /Ig  transfer the first signalc. Signaling pathwaysd. Effect of coreceptors (CD21/CD19/CD81) Transduction of signals by the B cell receptorIgaIgbIntracytoplasmicsignalling domainsExtracellular antigenrecognition domainsThe cytoplasmic domains of the Iga and Igb contain Immunoreceptor Tyrosine -based Activation Motifs (ITAMS) - 2 tyrosine residues separated by 9-12 amino acids - YXX[L/V]X6-9YXX[L/V]BCR Signaling IBCR Signaling IIThe role of co-receptors (CD19/CD21/CD81) in B cell activation2) Role of Th cells in humoral immune response to TD-Ag•For a protein Ag to stimulate Ab response, B cells and Th cells specific for that Ag must come together in lymphoid organs and interact in a way that stimulates B cell proliferation and differentiation.a. Activation and migration of helper T cells•Th cells that have been activated to differentiate into effector cells interact with antigen-stimulated B cells at the edges of lymphoid follicles in the peripheral lymphoid organs.The interactions of Th cells and B cells in lymphoid tissues.b. Presentation of Ags by B cells to Th cells•B cells that bind protein Ags by their BCR endocytose these Ags, process them in endosomal vesicles, display MHC II-peptides for recognition of Th cells. •B cells and Th cells recognize different epitopes of the same protein Ag.Ag presentation by B cells to Th cellsc. Mechanisms of Th cell-mediated activation of B cells•Th cells that recognize Ag presented by B cells activate B cells by expressing CD40L and by secreting cytokines (IL-2, IFN-, IL-4, IL-5, IL-6, IL-13, etc.).Mechanisms of Th cell-mediated activation of B cellsKey components of T cell help•CD40L triggers CD40 -> synergizes with BCR signals to promote mitosis; cytokine (e.g. IL4) signals also contribute•FasL triggers Fas -> BCR signaling protects from apoptosis•T cell derived cytokines influence differentiation, isotype switching:–IL2, IL6 promote differentiation–IL4 -> IgG1, IgE–IFN -> IgG2a, IgG3–TGFb and IL5 > IgA•Many other molecules involved in T-B interactions –e.g. ICAM1/LFA1, ICOS/ICOSL, CD30/CD30L, CD27L/CD27, OX40L/OX40, ...d. Th cells stimulate B cells to produce Abs of different heavy chain classes (isotypes)•Heavy chain class switching is initiated by CD40L-mediated signals, and switching to different classes is stimulated by different cytokines.Ig heavy chain class (isotype) switching（蠕虫）Ig heavy chain class (isotype) switchingMechanisms of Ig heavy chain class switchinge. Affinity maturation in Ab responses•Affinity maturation is the process by which the affinity of Abs produced in response to a protein Ag increases with prolonged and repeated exposure to that Ag.•The increase in affinity is due to point mutations in the V regions, and particularly in the Ag-binding HVR, of the Abs produced.•Affinity maturation occurs in the germinal centers of lymphoid follicles.Affinity maturation in antibody responses – somatic mutationControl of Affinity & Affinity MaturationFive B cell antigenreceptors - all specificfor , but withdifferent affinitiesdue to somatichypermutationof Ig genes in the germinal centreBBBBBOnly this cell, that has a high affinity for antigen can express CD40.Only this cell can receive signal 2Only this cell is rescued from apoptosis i.e. clonally selectedThe cells with lower affinity receptors die of apoptosis by neglect Affinity maturation in antibody responses - Selection of high affinity B cellsThe anatomy of humoral immune responses•A fraction of the activated B cells, which are often the progeny of class-switched high-affinity B cells, do not differentiate into Ab secretors but instead become memory B cells.Germinal CentersFunction: to generate B cells that produce antibodies with increased affinity for the inducing antigen => affinity maturationGerminal Center Reaction:Activated B cells give rise to Centroblasts （中心母（中心母细胞）胞）- localize in follicle, undergo rapid cell division and turn on machinery that causes somatic mutation in V-regionsCentroblasts give rise to Centrocytes （生（生发中心中心细胞）胞）- migrate to the FDC-rich region of the Germinal Center- survival is dependent on interaction with FDC-bound Ag and presentation of Ag to T cells- centrocytes that successfully compete to bind antigen (e.g. by having higher affinity BCR) and to receive T cell help are selected and may differentiate into long-lived plasma cells or memory B cellsAssociation of antigen with FDCin the form of an immune complex with C3d and antibodies attachedAntigen enters the germinal centreComplement receptor 3Ig Fc receptorFDC surfaceThe filiform dendrites of FDC develop beads coated with a thin layer of immune complexesThe Immune complexes bind to Fc and complement receptors on the FDC dendritesThe veils of antigen-bearing dendritic cell surround the beads and the layer of immune complexes is thickened by transfer from the dendritic cell. These beads are then released and are then called ICCOSOMESIccosome formation and releaseDC veilsIccosomes (black coated particles) bind to and are taken up by B cellsurface immunoglobulinYYYIccosomes bearing different antigensBUptake of Iccosomes/Antigen by B cellsAnti- B cellSurface Ig captures antigenCross-linking of antigen receptor activates B cellActivated B cell expresses CD40CD40Germinal Centers3. B cell response to TI-Ag* TI-1 (B cell mitogen) activate B cells- Antigen crosslink to BCR and mitogen receptors-Or simpely crosslink mitogen receptors in a high dose (LPS) * TI-2 activate mature B cells directly -the repeated epitopes combine with BCR→ BCR cross-linking→produce IgM (bacteria capsular polysaccharides)3. Immune response of B cells to TI-AgNo Th help，no memory, early effectTDependentAntigensTI-1AntigensTI-2AntigensInduces response in babiesYesYesNoInduces response in athymiaNoYesYesPrimes T cellsYesNoNoPolyclonally activates B cellsNoYesNoRequires repeating epitopesNoNoYesT Dependent & Independent AntigensExamplesTD: Diptheria toxin, influenza heamagglutinin, Mycobacterium tuberculosisTI-1: Bacterial lipopolysaccharides, Brucella abortisTI-2: Pneumococcal polysaccharides, Salmonella polymerised flagellinTD: Activate B-1 and B-2 B cellsTI-1: Activate B-1 and B-2 B cellsTI-2: Activate only B-1 B cellsPrimary immune response - longer latent phase; - smaller peak response (lower Ab titer); - remaining in the serum at detectable levels for much shorter periods; - lower average affinity; - usually IgM;4. General features of Ab responses in vivo(The immune response followed by secondary antigenic challenge) - shorter latent phase; - bigger peak response (higher Ab titer); - remaining in the serum at detectable levels for much longer periods; - higher average affinity; - usually IgG.Secondary immune responseFeatures of primary and secondary antibody responses。