浙江大学医学免疫学经典课件免疫9、13-B细胞.ppt

Lie Wang(,汪洌）,浙江省杭州市浙江大学紫金港校区,医学院科研楼,A810-814,医学院免疫学研究所,B lymphocytes and,Humoral Immune Response,The discovery of B cell immunity,1954-Bruce Glick,Ohio State University,Studies 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 called B cells,Mammals do not have a bursa of Fabricius,Transfer marked foetal,liver cells,Origin of B cells and organ of B cell,maturation,No Mature,B cells,After birth,development continues in the bone marrow,Normal bone marrow,Defective bone marrow,Mature marked,B cells,in periphery,B cell development starts in the foetal liver,B cell development in the bone marrow,B,Regulates construction of an antigen receptor,Bone Marrow provides a,MATURATION&DIFFERENTIATION MICROENVIRONMENT,for B cell development,Ensures each cell has only one specificity,B,Checks and disposes of self-reactive B cells,B,Exports useful cells to the periphery,B,Provides a site for antibody production,B,Secreted,Factors-CYTOKINES,2.Secretion of cytokines by stromal cells,B,Bone marrow stromal cells nurture developing B cells,Types of cytokines and cell-cell contacts needed at each stage of differentiation are different,Stromal cell,1.Specific cell-cell contacts between stromal cells and developing B cells,Cell-cell contact,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,),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 are,defined by Ig gene rearrangement,B CELL STAGE,IgH GENE,CONFIGURATION,Stem cell,Early pro-B,Late pro-B,Large pre-B,Germline,D,H,to J,H,V,H,to D,H,J,H,V,H,D,H,J,H,Pre-B cell,receptor,expressed,Ig light chain gene has not yet rearranged,B cell receptor,Transiently expressed when V,H,D,H,J,H,C,H,m,is productively rearranged,Ig,a,&Ig,b,signal,transduction,molecules,C,H,m,Heavy chain,V,H,D,H,J,H,Light chain,V,L,J,L,C,L,VpreB,l,5,Pre-,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 RNA,C,m,1,C,m,2,C,m,3,C,m,4,C,d,1,C,d,2,C,d,3,pA1,V,D,J,C,m,1,C,m,2,C,m,3,C,m,4,C,d,1,C,d,2,C,d,3,V,D,J,AAA,RNA cleaved and polyadenylated at pA2,V,D,J,C,m,IgM mRNA,V,D,J,C,d,IgD mRNA,C,g,1,C,g,3,C,d,C,m,V,D,J,C,m,1,C,m,2,C,m,3,C,m,4,C,d,1,C,d,2,C,d,3,DNA,pA1,pA2,V,D,J,Two types of mRNA can be made simultaneously in the cell by differential usage of alternative polyadenylation sites and splicing of the RNA,RNA cleaved and polyadenylated at pA1,AAA,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 only one specificty ofAb expressed per cell,Large,Pre-B,Stromal cell,Unconfirmed ligand of pre-B cell receptor,2.Triggers entry into cell cycle,ALLELIC EXCLUSION,Expression 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 V,H,D,H,J,H,joins,Evidence for allelic exclusion,Allotypes can be identified by staining B cell surface Ig with antibodies,a/a,b/b,a/b,Y,B,b,Y,B,a,Y,B,b,Y,Y,B,a,b,Y,B,a,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 per cell,(Refer back to Dreyer&Bennet hypothesis in Molecular Genetics of Immunoglobulins lecture topic),Y,Y,Y,Y,Suppression of H chain gene rearrangement,ensures only one specificity of Ab expressed per cell.,Allelic exclusion prevents unwanted responses,B,Self antigen,expressed by,e.g.brain cells,S.aureus,Y,Y,Y,Y,Y,B,S.aureus,Y,Y,Y,Y,Y,Y,Y,Anti,S.aureus,Antibodies,Y,Y,Y,Y,Y,Y,Anti,brain,Abs,One Ag receptor per cell,IF,there were two Ag receptors per cell,Y,Y,Y,Y,Y,Y,Y,Anti,S.aureus,Antibodies,Prevents induction of unwanted responses by pathogens,Allelic exclusion is needed for efficient clonal selection,All daughter cells must express the same Ig specificity,otherwise the efficiency of the response would be compromised,Suppression of H chain gene rearrangement helps prevent the emergence of,new daughter specificities during proliferation after clonal selection,S.typhi,Antibody,S.typhi,Allelic exclusion is needed to prevent holes in the repertoire,Exclusion of anti-brain B cells i.e.self tolerance,Y,Y,B,B,One specificity of Agreceptor per cell,S.aureus,Anti-brain Ig,AND,anti-,S.aureus,Ig,Y,Y,Y,B,B,IF,there were two specificitiesof Ag receptor per cell,Anti-brain Ig,B,B,Deletion,Anergy,OR,anti,S.aureus,B cells will be excluded leaving a“hole in the repertoire”,BUT,Y,Y,Y,B,B,1.Suppresses further H chain rearrangement,Ligation of the pre-B cell receptor,1.Ensures only one specificity ofAb expressed per cell,Large,Pre-B,Stromal cell,Unconfirmed ligand of pre-B cell receptor,2.Triggers entry into cell cycle,2.Expands only the pre-Bcells with in frame V,H,D,H,J,H,joins,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Large,Pre-B,Proliferation,Y,Immature,B cell,Light chain expressed,IgM displayed on surface,IgM,Ligation of the pre-B cell receptor triggers entry into the cell cycle,Large,pre-B,Many large pre-B cells with identical pre-B receptors,Large pre-B,Intracellular VDJC,H,chain,V,L,-J,L,rearranges,Proliferation stops,Pre-receptor not displayed,Small pre-B,B,Y,Y,Y,Y,B,Small pre-B cell,No antigen receptor at cell surface,Unable to sense Ag environment,!,May be self-reactive,!,Immature B cell,Cell surface Ig expressed,Able to sense Ag environment,Can now be checked for self-reactivity,Acquisition of antigen specificity creates a need,to check for recognition of self antigens,Physical removal from the repertoire,DELETION,Paralysis of function,ANERGY,Alteration of specificity,RECEPTOR EDITING,B cell self tolerance:clonal deletion,Immature,B cell recognises,MULTIVALENT,self Ag,B,Clonal deletion by,apoptosis,Y,Y,B,Immature,B,B,Small,pre-B,Small pre-B cell,assembles Ig,Y,B cell self tolerance:anergy,B,Y,Y,Y,B,Anergic B cell,IgD normal IgM low,Immature,B cell recognises,soluble self Ag,No cross-linking,Y,Y,B,Immature,B,B,Small,pre-B,Small pre-B cell,assembles Ig,IgM,IgD,IgD,IgD,Receptor editing,A rearrangement encoding a self specific receptor can be replaced,V,C,D,J,V,V,V,Y,B,B,!,Receptor,recognises,self antigen,!,B,Apoptosis,or anergy,Y,B,B,Edited receptor now recognises,a different antigen and can be,rechecked for specificity,C,D,J,V,V,V,V,Arrest development,And reactivate,RAG-1 and RAG-2,Y,Y,Y,Y,Y,Y,Mature B cell,exported to the,periphery,Y,Y,B cell self tolerance:export of self tolerant B cells,IgD and IgM normal,IgM,IgD,IgD,IgD,IgD,IgM,IgM,IgM,Immature,B cell doesnt recognise any,self Ag,Y,Y,B,Immature,B,B,Small,pre-B,Small pre-B cell,assembles Ig,B,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,（,CD11,/CD18),：,mediate cell-cell interaction and co-stimulation,3.Co-stimulatory molecules,CD20:,function is unclear.It is suspected that it acts as a,calcium channel,in the,cell membrane,CD22,：,Inhibitory receptor with ITIM motif,CD32(Fc,RII,),：,Inhibitory receptor,Cytokine receptors,Complement Receptors,Toll-like receptors,MHC,4.Other receptors,3.Subtype of B cells,Conventional B cells(B-2 cells),B-1 cells(expression of CD5),CD5,Two B cell lineages,B,B cell precursor,B,Mature B cell,B2 B cells,Plasma cell,Y,Y,Y,Y,Y,Y,Y,Y,Y,PC,IgG,B,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,Y,IgM-no other isotypes,B,Distinct 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 blood,mIg:IgM,IgD,Produce 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 properties,Property,B-1 cellsB-2 cells,N regions,FewExtensive,V region repertoire,RestrictedDiverse,Location,Peritoneum/pleuraEverywhere,Renewal,Self renewal in situBone marrow,Spontaneous Ig production,HighLow,Isotypes,IgMIgM/G/A/D/E,Carbohydrate specificity,YesRarely,Protein specificity,RarelyYes,Need T cell help,NoYes,Somatic hypermutation of Ig,NoHigh,Memory development,NoYes,Yes Rarely,Rarely Yes,No Yes,Carbohydrate specificity,Protein specificity,Need T cell help,Specificity&requirement for 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.,2.Ag presentation to T cells,3.Immune regulation,Secretion of cytokines(TNF,IFN,IL-12)M,DC,NK,B cell.,Co-stimulation of T cellsT cell proliferation.,Y,Y,Immune effector mechanisms against extracellular pathogens&toxins,NEUTRALISATION,Y,Toxin release,blocked,Prevents,toxicity,NEUTRALISING ANTIBODIES,Adhesion to,host cells blocked,Prevents,invasion,Bacterium,Y,Toxin,Fc receptor,binding,Effector mechanisms against extracellular pathogens,OPSONISATION,OPSONISATION,Phagocytosis,Bacteria in extracellular space,Ab,+,Effector mechanisms against extracellular pathogens,COMPLEMENT Activation,Bacteria in plasma,Ab&,COMPLEMENT,+,Phagocytosis,binding,Complement&,Fc receptor,Lysis,Opsonisation,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-Ag,1)B cells recognize TD-Ag,a.BCR directly recognizes B cell epitopes,b.Ig,/Ig,transfer the first signal,c.Signaling pathways,d.,Effect of,coreceptors(CD21/CD19/CD81),Transduction of signals by the B cell receptor,Ig,a,Ig,b,Intracytoplasmicsignalling domains,Extracellular antigen,recognition domains,The cytoplasmic domains of the Ig,a,and Ig,b,contain Immunoreceptor Tyrosine-based Activation Motifs(ITAMS)-2 tyrosine residues separated by 9-12 amino acids-,Y,XXL/VX,6-9,Y,XXL/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,g,-IgG2a,IgG3,TGF,b,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 Maturation,Five B cell antigenreceptors-all specificfor ,but withdifferent affinities,due to somatichypermutationof Ig genes in the germinal centre,B,B,B,B,B,Only this cell,that has a high affinity for antigen can express CD40.Only this cell can receive signal 2,Only 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 fraction of the activated B cells,which are often the progeny of class-switched hig