浙江大学医学免疫学经典课件免疫9、13B细胞文档资料.ppt

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1、,The discovery of B cell immunity,1954-Bruce Glick,Ohio State UniversityStudies on the function of the bursa of Fabricius,a lymphoid organ in the cloacal region of the chicken,Bursa was later found to be the organ in which antibody producing cells developed antibody producing cells were thereafter c

2、alled B cellsMammals do not have a bursa of Fabricius,Origin of B cells and organ of B cellmaturation,After birth,development continues in the bone marrow,B cell development starts in the foetal liver,B cell development in the bone marrow,Bone Marrow provides aMATURATION&DIFFERENTIATION MICROENVIRON

3、MENTfor B cell development,Bone marrow stromal cells nurture developing B cells,Types of cytokines and cell-cell contacts needed at each stage of differentiation are different,Bone marrow stromal cell,Maturing B cells,B,B,Stromal cell,B lineage commitment,HSC(hematopoietic stem cell)MPP(淋巴系髓系多能前体细胞)

4、ELP(earliest lymphocyte progenitor)ETP(early T-lineage progenitor)CLP(common lymphoid progenitor),HSC,Development and migration of B cells(An overview),Stages of differentiation in the bone marrow aredefined by Ig gene rearrangement,B CELL STAGEIgH GENECONFIGURATION,Stem cell,Early pro-B,Late pro-B,

5、Large pre-B,Germline,DH to JH,VH to DHJH,VHDHJH,Ig light chain gene has not yet rearranged,B cell receptor,Transiently expressed when VHDHJH CHm is productively rearranged,Pre-,B cell development is coupled with rearrangement of heavy-chain,B cell development is coupled with rearrangement of heavy-c

6、hain,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 RNA,Two types o

7、f mRNA can be made simultaneously in the cell by differential usage of alternative polyadenylation sites and splicing of the RNA,B cell development is coupled with rearrangement of heavy-chain,6000 heavy chains combined with 320 light chains 1.9X106 Abs,Ligation of the pre-B cell receptor,1.Ensures

8、only one specificty ofAb expressed per cell,2.Triggers entry into cell cycle,ALLELIC EXCLUSIONExpression of a gene on one chromosome prevents expression of the allele on the second chromosome,1.Suppresses further H chain rearrangement,2.Expands only the pre-Bcells with in frame VHDHJH joins,Evidence

9、 for allelic exclusion,Allotypes can be identified by staining B cell surface Ig with antibodies,AND,ALLOTYPE-polymorphism in the C region of Ig one allotype inherited from each parent,Suppression of H chain rearrangement by pre-B cell receptor prevents expression of two specificities of antibody pe

10、r cell(Refer back to Dreyer&Bennet hypothesis in Molecular Genetics of Immunoglobulins lecture topic),Suppression of H chain gene rearrangementensures only one specificity of Ab expressed per cell.,Allelic exclusion prevents unwanted responses,One Ag receptor per cell,IF there were two Ag receptors

11、per cell,Prevents induction of unwanted responses by pathogens,Allelic exclusion is needed for efficient clonal selection,All daughter cells must express the same Ig specificityotherwise the efficiency of the response would be compromised,Suppression of H chain gene rearrangement helps prevent the e

12、mergence ofnew daughter specificities during proliferation after clonal selection,Antibody,Allelic exclusion is needed to prevent holes in the repertoire,Exclusion of anti-brain B cells i.e.self tolerance,Anti-brain IgANDanti-S.aureus Ig,Anti-brain Ig,anti S.aureus B cells will be excluded leaving a

13、“hole in the repertoire”,BUT,1.Suppresses further H chain rearrangement,Ligation of the pre-B cell receptor,1.Ensures only one specificity ofAb expressed per cell,2.Triggers entry into cell cycle,2.Expands only the pre-Bcells with in frame VHDHJH joins,Ligation of the pre-B cell receptor triggers en

14、try into the cell cycle,Many large pre-B cells with identical pre-B receptors,Small 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-reactivity,Acquisition

15、 of antigen specificity creates a needto check for recognition of self antigens,Physical removal from the repertoireDELETIONParalysis of functionANERGYAlteration of specificityRECEPTOR EDITING,B cell self tolerance:clonal deletion,Immature B cell recognisesMULTIVALENTself Ag,Clonal deletion byapopto

16、sis,Y,B cell self tolerance:anergy,Y,Y,Y,Anergic B cell,IgD normal IgM low,Immature B cell recognisessoluble self AgNo cross-linking,IgM,IgD,IgD,IgD,Receptor editing,A rearrangement encoding a self specific receptor can be replaced,V,V,V,V,V,V,V,Y,Y,Y,Y,Y,Y,Mature B cellexported to theperiphery,Y,Y,

17、B cell self tolerance:export of self tolerant B cells,Immature B cell doesnt recognise anyself Ag,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.

18、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-rec

19、eptors,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（CD11/CD18)：mediate cell-cell interaction and co-stimulation,3.Co-stimulatory molecules,CD20:function is unclear.It is

20、 suspected that it acts as a calcium channel in the cell membraneCD22：Inhibitory receptor with ITIM motifCD32(FcRII)：Inhibitory receptorCytokine receptorsComplement ReceptorsToll-like receptorsMHC,4.Other receptors,3.Subtype of B cells,Conventional B cells(B-2 cells)B-1 cells(expression of CD5),Two

21、B cell lineages,B2 B cells,IgM-no other isotypes,B1 B cellsPrimitive 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

22、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 defe

23、nce 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 properties,PropertyB-1 cellsB-2 cellsN regionsFewExtensiveV region repertoireRestricte

24、dDiverseLocationPeritoneum/pleuraEverywhereRenewalSelf renewal in situBone marrowSpontaneous Ig productionHighLowIsotypesIgMIgM/G/A/D/ECarbohydrate specificityYesRarelyProtein specificityRarelyYesNeed T cell helpNoYesSomatic hypermutation of IgNoHighMemory developmentNoYes,Specificity&requirement fo

25、r T cell help suggests strikingly different typesof antigens are seen by B-1 and B-2 B cells,4.Function of B cells,1.Production of antibody Abs prevent microorganism from entry into cells and eliminate microorganisms by opsonization causing phagocytosis,complement activation and toxin neutralization

26、.2.Ag presentation to T cells3.Immune regulation Secretion of cytokines(TNF,IFN,IL-12)M,DC,NK,B cell.Co-stimulation of T cellsT cell proliferation.,Immune effector mechanisms against extracellular pathogens&toxinsNEUTRALISATION,NEUTRALISING ANTIBODIES,Bacterium,Toxin,Effector mechanisms against extr

27、acellular pathogensOPSONISATION,OPSONISATION,Effector mechanisms against extracellular pathogensCOMPLEMENT Activation,Lysis,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 eliminat

28、e 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-dependentTI-Ag：T cell-independent,Response to TD-Ag,1)B cells recognize TD-Ag a.BCR directly recognizes B cell epitope

29、s b.Ig/Ig transfer the first signalc.Signaling pathwaysd.Effect of coreceptors(CD21/CD19/CD81),Transduction of signals by the B cell receptor,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 pro

30、tein 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 effect

31、or 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 t

32、hem 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 activa

33、te 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 contributeFasL triggers

34、Fas-BCR signaling protects from apoptosisT cell derived cytokines influence differentiation,isotype switching:IL2,IL6 promote differentiationIL4-IgG1,IgEIFNg-IgG2a,IgG3TGFb and IL5 IgAMany other molecules involved in T-B interactions e.g.ICAM1/LFA1,ICOS/ICOSL,CD30/CD30L,CD27L/CD27,OX40L/OX40,.,d.Th

35、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)switc

36、hing,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

37、 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 Maturation,Only this cell,that has a high affinity for antigen c

38、an express CD40.Only this cell can receive signal 2Only this cell is rescued from apoptosis i.e.clonally selected,The 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

39、 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 Centers,Function:to generate B cells that produce antibodies with increased affinity for the inducing antigen=affi

40、nity maturationGerminal Center Reaction:Activated B cells give rise to Centroblasts（中心母细胞）-localize in follicle,undergo rapid cell division and turn on machinery that causes somatic mutation in V-regionsCentroblasts give rise to Centrocytes（生发中心细胞）-migrate to the FDC-rich region of the Germinal Cent

41、er-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

42、 of antigen with FDC,in the form of an immune complex with C3d and antibodies attached,Antigen enters the germinal centre,The 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

43、thickened by transfer from the dendritic cell.These beads are then released and are then called ICCOSOMES,Iccosome formation and release,Iccosomes(black coated particles)bind to and are taken up by B cellsurface immunoglobulin,Iccosomes bearing different antigens,Uptake of Iccosomes/Antigen by B cel

44、ls,Surface Ig captures antigen,Cross-linking of antigen receptor activates B cell,Activated B cell expresses CD40,CD40,Germinal Centers,3.B cell response to TI-Ag,*TI-1(B cell mitogen)activate B cells-Antigen crosslink to BCR and mitogen receptorsOr simpely crosslink mitogen receptors in a high dose

45、(LPS)*TI-2 activate mature B cells directly-the repeated epitopes combine with BCR BCR cross-linkingproduce IgM(bacteria capsular polysaccharides),3.Immune response of B cells to TI-Ag,No Th help，no memory,early effect,Induces response in babiesYesYesNoInduces response in athymiaNoYesYesPrimes T cel

46、lsYesNoNoPolyclonally activates B cellsNoYesNoRequires repeating epitopesNoNoYes,T Dependent&Independent Antigens,ExamplesTD:Diptheria toxin,influenza heamagglutinin,Mycobacterium tuberculosisTI-1:Bacterial lipopolysaccharides,Brucella abortisTI-2:Pneumococcal polysaccharides,Salmonella polymerised

47、flagellin,TD: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.Ge

48、neral 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,