抗原的加工和递呈.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,资料仅供参考,不当之处，请联系改正。,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,资料仅供参考,不当之处，请联系改正。,T cells do not recognise native antigens,Y,Y,B,Y,Y,Y,Y,Y,Y,Y,B,Y,T,Y,T,活化增殖、产生抗体,无增殖,无,CK,产生,BCR,交联,Y,B,Y,B,Y,B,Y,B,Y,B,Y,B,Y,B,Cell surface,peptides,of Ag,Antigens must be processed in order,to be recognised by T cells,Y,T,T cell,r,esponse,无应答,无应答,无应答,无应答,Soluble,native Ag,Cell surface,native Ag,Soluble,peptides,of Ag,抗原肽,-MHC,复合物,抗原加工、递呈,基本内容,基本概念,抗原递呈细胞的种类,抗原加工和递呈的途径,抗原加工递呈的生理意义,一、基本概念,抗原加工,：蛋白质抗原在细胞内被降解成能与,MHC,分子结合的肽的过程。,抗原递呈,：,MHC,分子与抗原肽结合，将其展示于细胞表面供,T,细胞识别的过程。,内源性抗原,：细胞内产生的蛋白质抗原，包括自身抗原和非己抗原,-MHC,分子递呈。,外源性抗原,：由细胞外摄入细胞内的蛋白质抗原，包括非己抗原和自身抗原,-MHC,分子递呈。,二、抗原递呈细胞的种类,APC,：即抗原递呈细胞，表达,MHC,和协同刺激分子，能够摄取、加工、处理抗原，并把抗原肽递呈给,T,细胞的一类特化的细胞群，包括,DC,、巨噬细胞、活化的,B,细胞和其他非专职,APC,。,APC,的分类：,非专职,APC,：内皮细胞、上皮细胞、纤维母细胞及脑内小胶质细胞等。,专职,APC,：,DC,、巨噬细胞、活化的,B,细胞,1.,树突状细胞,(dendritic cell,DC),由美国学者,Steinman,于,1973,年发现，因其伸出树枝样突起而得名。,1993,年,Inaba,等用,GM-CSF,体外扩增获得成功。,根据来源：分为髓系来源的,DC,和淋巴系来源的,DC,。,根据分布：淋巴组织中的,DC(,并指状,DC,，边缘区,DC,）；非淋巴样组织中的,DC,（间质性,DC,、郎格罕斯细胞）；体液中的,DC,（隐蔽细胞，血液,DC,）,图,2-4,呈集落悬浮生长的成熟,DC,（,400,）,Fig2-4 Mature DC suspended in media by colony,（,400,）,图,2-5,呈散在生长的成熟,DC,（,400,）,Fig2-5 scattered mature DC,（,400,）,DC,的特点及功能：,通过形态学、组合性表面标志及在混合淋巴细胞反应中能够刺激初始,T,细胞增殖鉴定。,人,DC,的主要特征性标志为,CD11c,、,CD1a,、,CD83,，是惟一能激活初始,T,细胞的,APC,。,是目前所知的机体内功能最强的,APC,，其抗原递呈功能是巨噬细胞的,10-100,倍。,通过三种方式摄取抗原：巨吞饮、受体介导的内吞作用、吞噬作用。,未成熟,DC,与成熟,DC,的区别：,摄取抗原的能力降低。,抗原加工、递呈功能增强。,MHC,、协同刺激分子（,CD80,、,CD86,）、黏附分子（,LFA-1,、,ICAM-1,）表达上调。,刺激,T,细胞增殖的能力增强。,2.,巨噬细胞（,macrophage,M,）,由血液中的单核细胞分化而来。,具有强大的吞噬功能（大吞噬细胞）。,可通过三种方式摄取抗原。,不能活化未致敏,T,细胞。,静止状态几乎不表达,MHC,和协同刺激分子。,3.B,细胞,主要加工和递呈可溶性抗原。,通过两种方式摄取抗原：胞饮、受体介导,通过,BCR,高效摄取抗原，具有浓集抗原的作用。,组成性表达,MHCII,类分子，但不表达协同刺激分子。,三、抗原加工和递呈的途径,经典途径：,MHC,类分子递呈内源性,Ag-CD8+T,MHC,类分子递呈外源性,Ag-CD4+T,非经典途径,-,交叉致敏,（一）外源性抗原的加工递呈,又称为,MHC,类途径。,分为抗原的摄取、加工、,MHC,类分子的合成与转运、,MHC,类分子荷肽、递呈几个阶段。,1.,外源性抗原的摄取,通过胞吞外源性抗原由细胞外进入细胞内，形成,内体,。,内体：,胞吞的抗原被质膜包围形成的空泡，是外源性抗原加工的场所。,内体经历早期、中期、晚期内体几个阶段，逐渐成熟，最终与溶酶体融合。,2.,外源性抗原的加工,外源性抗原在内体的酸性环境和各种组织蛋白酶的作用下被降解成适于与,MHC,类分子结合的肽。,3.MHC,类分子的生物合成和转运,合成场所：粗面内质网,/,二聚体与,Ii,链,结合，形成,Ii3,3,3,Ii,链：,Ia,分子相关的不变链（,Ia-associated,invariant chain,Ii,链）,CLIP,：,Ii,链中,81,-104,位氨基酸残基的特殊肽段结构，能与所有,MHC,类分子的抗原结合槽以不同亲和力结合，称为,类分子结合的不变肽链（,class II associated invariant peptide,CLIP),Ii,链的作用：,帮助,II,类分子折叠和装配,阻止,II,类分子与,ER,中新合成的肽或内源性抗原肽结合,引导,II,类分子进入内体,4.MHC,类分子荷肽,荷肽：,MHC,分子与抗原肽结合的过程，,在,M,C,和,C,V,中进行。,M,C,和,C,V,：,M,C,即,MHC,类区室（,MHC class,compartment),，,C,V,即含,MHC,类分子的空泡（,MHC class-cintaining vesicles),是富含外源性抗原肽和,HLA-DM,分子的内体。,MHC,类分子荷肽过程：,（,1,）蛋白水解酶降解,Ii,链，,CLIP,与,II,类分子结合。,（,2,）,HLA-DM,分子与,HLAII-CLIP,复合物结合。,（,3,）,CLIP,脱离抗原结合槽，抗原结合槽处于开放状态。,（,4,）具有合适锚定基的高亲和力外源性抗原肽进入抗原结合槽，,HLA-DM,解离。,5.,外源性抗原的递呈,通过胞吐作用，空泡膜与细胞膜融合，外源性抗原肽,-II,类分子表达于,APC,表面，供,CD4+T,细胞识别。,Y,Y,Pinocytosis,Phagocytosis,Membrane Ig,receptor mediated,uptake,Y,Uptake of exogenous antigens,Complement receptor,mediated phagocytosis,Y,Fc receptor mediated phagocytosis,Uptake mechanisms direct antigen into intracellular vesicles,for exogenous antigen processing,100,50,75,25,0,%of max.,T cell,response,10,-1,10,-2,10,-3,Antigen,gml,-1,Receptor-mediated,antigen uptake,Non-receptor,-mediated uptake,Receptor-mediated uptake enhances the,efficiency of the T cell response,Proteases produce 24 amino acid long peptides from antigens,Drugs that raise the pH of endosomes inhibit antigen processing,Endosomes,Exogenous pathway,Increase,in acidity,Cell surface,To lysosomes,Uptake,Protein antigens,In endosome,Cathepsin B,D and L proteases are activated by the decrease in pH,Activation of Cathepsin B at low pH,At higher pH cathepsin B exists in a pro-enzyme form,Acidification of the endosome alters the conformation of the proenzyme to allow cleavage of the pro-region,Loss of the pro-region exposes the catalytic site of the protease,Hence:drugs that alter acidification of the endosomes disturb exogenous antigen processing,Need to prevent newly synthesised,unfolded self proteins from binding to immature MHC,Invariant chain stabilises MHC class II by non-covalently binding to the immature MHC class II molecule and forming a nonomeric complex,In the endoplasmic reticulum,MHC class II maturation and invariant chain,Invariant chain structure,Three extended peptides each bind into the grooves of three MHC class II molecules to form the nonomeric complex,A peptide of the invariant chain blocks the MHC molecule binding site.,This peptide is called the,CL,ass II associated,I,nvariant chain,P,eptide(,CLIP,),Invariant chain CLIP peptide,and,b,chains of MHC class II molecules,CLIP,Endosomes,Cell surface,Uptake,Class II associated invariant chain peptide(CLIP),(,inv)3 complexes,directed towards,endosomes by,invariant chain,Cathepsin L degrades Invariant chain,CLIP blocks groove in MHC molecule,MHC Class II,containing vesicles,fuse with antigen,containing vesicles,Removal of CLIP,?,How can the peptide stably bind to a floppy binding site?,Competition between large number of peptides,HLA-DM,HLA-DR,HLA-DM assists in the removal of CLIP,HLA-DM:Crystallised without a peptide in the groove,In space filling models the groove is very small,HLA-DM,HLA-DR,Single pocket in“groove”,insufficient to accommodate,a peptide,Multiple pockets,in groove sufficient to,accommodate a peptide,HLA-DM catalyses the removal of CLIP,MIIC compartment,HLA-DM,Replaces CLIP with a peptide antigen using a catalytic mechanism(i.e.efficient at sub-stoichiometric levels),Discovered using mutant cell lines that failed to present antigen,HLA-DO may also play a role in peptide exchange,Sequence in cytoplasmic tail retains HLA-DM in endosomes,HLA-DM,HLA-DR,MIIC compartment sorts peptide-MHC complexes for surface expression or,lysosomal degradation,Surface expression of MHC class II-,peptide complexes,Exported to the cell surface(t1/2=50hr),Sent to lysosomes for degradation,（二）内源性抗原的加工递呈,又称为,MHC,类途径。,分为内源性抗原的加工、转运、,MHC,类类分子荷肽、递呈几个阶段。,1.,内源性抗原的加工,蛋白酶体：一种存在于大多数细胞内的大分子多重蛋白酶复合体,蛋白酶体将胞内蛋白质降解，在,LMP2,和,LMP7,的作用下产生,6-10,个氨基酸残基的肽。,2.,内源性抗原肽的转运,由,TAP,选择性的将,8-15,个氨基酸残基的肽转运到内质网。,TAP,分子位于内质网膜上，其跨膜段在内质网膜上环绕形成跨膜孔道。,3.MHC,类分子荷肽,在内质网中进行,在钙联蛋白、钙网蛋白的协助下折叠形成,/,2m,二聚体，通过,TAP1,相关蛋白的作用结合于内质网孔道的内侧口，并与内源性抗原肽结合。,4.,内源性抗原肽的递呈,结合了肽的,I,类分子在高尔基体中与,TAP1,相关蛋白解离，通过外吐空泡运送到细胞表面，供,CD8+T,细胞识别。,Degradation in the proteasome,The components of the proteasome include MECL-1,LMP2,LMP7,These components are induced by IFN-,and replace constitutive components to confer proteolytic properties.,LMP2&7 encoded in the MHC,Proteasome cleaves proteins after hydrophobic and basic amino acids and releases peptides into the cytoplasm,Cytoplasmic cellular proteins,including non-self proteins,are degraded continuously by a multicatalytic protease of 28 subunits,Crystal Structure Of The 20s Proteasome,From Yeast,View,End on,ENDOPLASMIC RETICULUM,CYTOSOL,Peptide antigens produced in the cytoplasm are physically separated from newly formed MHC class I,Newly synthesised,MHC class I molecules,Peptides need,access to the ER in,order to be loaded onto MHC class I molecules,ER membrane,Lumen of ER,Cytosol,Transporters associated with,antigen processing(TAP1&2),Transporter has preference for 8 amino acid peptides,with hydrophobic C termini.,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,ER membrane,Lumen of ER,Cytosol,TAP-1,TAP-2,Peptide,ATP-binding cassette,(ABC)domain,Hydrophobic,transmembrane,domain,Peptide antigens,from proteasome,Endoplasmic reticulum,Calnexin binds,to nascent,class I,chain,until,2-M binds,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,B2-M binds and stabilises floppy MHC,Tapasin,calreticulin,TAP 1&2 form a complex with the floppy MHC,Cytoplasmic peptides are loaded onto the MHC molecule and the structure becomes compact,Maturation and loading of MHC class I,Fate of MHC class I,Sent to lysosomes for degradation,Exported to the cell surface,Endoplasmic reticulum,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,Peptide,TAP-1,TAP-2,HSV protein blocks transport,of viral peptides into ER,Sent to lysosomes,for degradation,Evasion of immunity by interference with endogenous antigen processing,（三）非经典递呈途径,-,交叉递呈,MHCI,类分子也能递呈外源性抗原，,MHCII,类分子也能递呈内源性抗原。,不是抗原递呈的主要方式。,四、抗原加工递呈的意义,实现免疫系统对非己抗原的免疫监视作用,免疫调节作用,小 结,基本概念：,APC,APC,的种类,内外性抗原加工递呈的过程,生理意义,