第 11 章 抗原的加工与递呈Antigen Processing & Presentation

T cells do not recognise native antigens

YYBYY Y Y YY

Y

BYT

YT

Proliferation and antibody production

No proliferationNo cytokine release

Cross-linking of surface membrane Ig

Y

B

Y

B Y

B

Y

B

Y

B Y

B

Y

B

Cell surfacepeptides

of Ag

Antigens must be processed in orderto be recognised by T cells

YT

T cellresponse

No T cellresponse

No T cellresponse

No T cellresponse

No T cellresponse

Solublenative Ag

Cell surfacenative Ag

Soluble peptides

of Ag

Cell surface peptides of Ag presented by cells that

express MHC antigens

ANTIGENPROCESSING

YT

MHC directs the response of T cells toforeign antigens

YTAg

YTAg

Anti response No anti response

MHC antigens PRESENT foreign antigens to T cells

Cells that present antigen are ANTIGEN PRESENTING CELLS

YT YTYTYT YBlockinganti-MHCantibody

YYY

Ag B 细胞 浆细胞 Ab

APC Th 细胞

Ag 肽 -MHC 分子 T细胞 Tc 细胞

Contents 抗原递呈细胞抗原加工递呈途径

第一节 抗原递呈细胞Antigen Presenting Cells

• 基本概念• 抗原递呈细胞

一、基本概念•抗原加工与递呈（ Antigen processing and presentation ）

–抗原加工是指蛋白质抗原在细胞内被降解成能与MHC 结合的肽的过程。–抗原递呈是指 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。

Influenza virus

•内源性抗原（ endogenous antigens ）

–指细胞内产生的蛋白质抗原•细胞产生的自身固有蛋白质•胞内寄生病毒或其它病原体产生的蛋白质•细胞恶性转化后产生的突变蛋白，即肿瘤抗原

–有核细胞内加工，由 MHCⅠ分子递呈

MM MM

Listeria

• 外源性抗原 (exogenous antigens)

–指由细胞外进入细胞的蛋白质抗原•细胞摄入的各种病原体和疫苗•在吞噬体和内体中生长的病原体•摄入的自身蛋白

–抗原递呈细胞内加工，由 MHCⅡ分子递呈

二、抗原递呈细胞• 抗原递呈细胞 (antigen presenting cell ， APC)– 能够摄取、加工、处理抗原并将 Ag 信息递呈给抗原特异性淋巴细胞（ T细胞）的一类免疫细胞。包括巨噬细胞、树突状细胞、成熟 B细胞等

•广义 APC–所有有核细胞–表达 MHCⅠ类分子

•专职 APC(professional APC)– MΦ， DC ， B细胞等–表达 MHCⅡ类分子

•兼职 APC(non-professional APC)–内皮细胞，上皮细胞，激活的 T细胞等–某些因素刺激后表达 MHC-Ⅱ类分子

1 、树突状细胞（ dendritic cell, DC ）• 典型树突状形态• 功能最强的 APC

DC 分类根据起源• 淋巴系 DC– 滤泡 DC (FDC)

• 髓系 DC（ CD11c+）– 郎格汉斯细胞 (LC)– 并指状 DC (IDC)

并指状树突细胞

滤泡状树突细胞

B 细胞

未成熟 DC和成熟 DC•未成熟 DC(Immature DC)

–皮肤、胃肠道、呼吸道等上皮内及实质器官间质内–摄取抗原并迁移至引流淋巴器官

•胞饮（吞饮）•受体介导内吞•吞噬弱

–表达低水平的 MHC 分子、协同刺激分子和粘附分子

•成熟过程中的重要变化 :–表达趋化因子受体，获得向引流淋巴结迁移的能力–加工递呈抗原，表达大量肽 -MHC 复合物–协同刺激分子和粘附分子表达上调

•成熟 DC(Mature DC)–淋巴结，脾及派氏集合淋巴管–高表达 MHC 分子、协同刺激分子及粘附分子–很强的抗原递呈能力

• 上皮组织中的 LC• 捕捉外来抗原后即进入引流淋巴结的 T细胞区，成为 IDC

2 、巨噬细胞(Macrophage, Mφ)

来源、分布• 前单核细胞（骨髓）• 单核细胞（血液）• 巨噬细胞（组织器官）

• 单核细胞体积较大，蹄状核（左，普通光镜）• 透射电镜显示其高尔基体发达、线粒体丰富、胞浆颗粒明显（中）• 扫描电镜显示腹腔巨噬细胞粘附于玻璃表面（右）

单 核 巨 噬 细 胞

功能• 吞噬消灭病原体• 加工递呈抗原，激发特异性免疫应答• 免疫应答的效应细胞

MΦ摄取抗原途径胞吞作用• 吞噬• 吞饮• 受体介导内吞

• 模式识别受体 （ pattern recognition receptors ， PRR ）

3、 B细胞

B 细胞摄取抗原途径•加工递呈可溶性抗原• BCR介导内吞

–特异性–高效性

第二节 抗原加工递呈途径Antigen Processing and Presentation Pathways• MHCⅡ类途径• MHCⅠ类途径• 非经典途径

概述• T 细胞不能直接识别游离蛋白 Ag ， 只能通过 TCR识别 Ag肽 -MHC 分子复合物• CD4+T---Ag 肽 -MHCⅡ分子复合物• CD8+T---Ag 肽 -MHCⅠ分子复合物

YThe site of pathogen replication or mechanism of

antigen uptake determines the antigen processing pathway used

Y

Cytosolic compartmentEndogenous processing

(Viral antigens)

Vesicular CompartmentContiguous with extracellular fluid

Exogenous processing(Streptococcal, Mycobacterial antigens)

INTRACELLULAR REPLICATION

EXTRACELLULAR ORENDOSOMAL REPLICATION

Y

Eliminated by:Killing of infected cells by CTL that use antigens generated by

ENDOGENOUS PROCESSING

YEliminated by:

Antibodies and phagocyteactivation by T helper cells

that use antigens generated byEXOGENOUS PROCESSING

Antigens generated by endogenous and exogenous antigen processing activate

different effector functions

ENDOGENOUS PATHOGENS

EXOGENOUSPATHOGENS

一、外源性抗原加工递呈途径• Exogenous processing and presentation pathway • MHC class Ⅱ pathway 外源性 Ag经 MHCⅡ类分子递呈

阶段：• 外源性抗原的摄取、加工• MHCⅡ类分子的合成及转运• MHCⅡ类分子荷肽• 递呈给 CD4+T 细胞

MHCⅡ类途径

1 、外源性抗原的摄取、加工处理• Uptake and degradation of exogenous antigens –APC以胞吞作用摄入 Ag，形成内体–内体与溶酶体融合形成内体 / 溶酶体–Ag 被蛋白酶降解成 Ag肽抗原加工区室（ compartments ）

Y Y

Pinocytosis

PhagocytosisMembrane Ig receptor mediated uptake

Y

Complement receptormediated phagocytosis Y

Fc receptor mediated phagocytosis

Uptake of exogenous antigens

APC以胞吞作用摄入 Ag，形成内体

Endosomes

Exogenous pathway

Increasein acidity

Cell surface

To lysosomes

Uptake Protein antigensIn endosome

Cathepsin B, D and L proteases are activated by the decrease in pH

2 、 MHCⅡ类分子的合成及转运• Biosynthesis and transportation of MHC classⅡ molecules –粗面内质网中 MHCⅡ类分子合成–与 Ii链结合成 (αβIi)3复合物

Need to prevent newly synthesised, self proteins from binding to immature

MHC

Invariant chain stabilises MHC class II by binding to the

immature MHC class II molecule

In the Endoplasmic ReticulumMHC class II maturation and invariant chain

Conception

• Ⅰi链– Ⅰa-associated invariant chain ，Ⅰ a 分子相关的不变链–协助Ⅱ类分子折叠和装配–阻止Ⅱ类分子与 ER中的新合成的肽或内源性抗原肽结合–引导Ⅱ类分子进入内体

Structure of invariant chain

Three extended peptides each bind into the grooves of three MHC class II molecules to form the nonomeric complex

CLass II associated Invariant chain Peptide (CLIP) A peptide of the invariant chain blocks the MHC molecule binding

site

CLIP of invariant chain

and chains of MHC class II molecules

CLIP

Conception

• CLIP– Class Ⅱ-associated invariant chain peptide ，Ⅱ类分子相关的不变链多肽– Ⅰi链中 81位至 104 位氨基酸残基的肽段结构– 能与所有 MHCⅡ类分子抗原结合槽相结合

3、 MHCⅡ类分子荷肽• Peptide-loading of MHC class Ⅱ molecules

– Ⅰi链引导下Ⅱ类分子进入内体 (MⅡC) – Ⅰi链降解，Ⅱ类分子肽结合槽中保留 CLIP– HLA-DM催化， CLIP 与肽结合槽解离– HLA-DM编选，高亲和力肽与Ⅱ类分子结合——Ag 肽 -MHCⅡ类分子形成

Endosomes

Cell surface

Uptake

Class II associated invariant chain peptide (CLIP)

(i)3 complexesdirected towardsendosomes byinvariant chain

Cathepsin L degrades Invariant chain

CLIP blocks groove in MHC molecule

MHC Class IIcontaining vesiclesfuse 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 catalyses the removal of CLIP

MIIC compartment

HLA-DMReplaces CLIP with a peptide antigen using

a catalytic mechanism

Sequence in cytoplasmic tail

retains HLA-DM in endosomes

HLA-DMHLA-DR

Conception• MⅡC

– MHC class Ⅱ compartment ， MHCⅡ类分子区室–富含外源性抗原肽、 MHCⅡ类分子、 HLA-DM的低 pH值的晚期内体– MHCⅡ类分子荷肽主要场所

• HLA-DM 的编选作用– HLA-DM可驱逐与Ⅱ类分子抗原结合槽低亲和 力结合的肽，直至有高亲和力的肽与Ⅱ类分 子结合，才与Ⅱ类分子分离，使其抗原结合 槽恢复闭合状态。– HLA这种对肽的选择作用称为 HLA-DM 的编选 作用，保证Ⅱ类分子递呈高亲和力的外源 性抗原肽。

4、递呈给 CD4+T 细胞• Presentation of exogenous antigen–Ag 肽 -Ⅱ类分子经胞吐作用表达于 APC 表面–供 CD4+T 细胞识别

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

Sent to lysosomes for degradation

二、内源性抗原加工递呈途径• Endogenous processing and presentation pathway • MHC class Ⅰ pathway 内源性 Ag加工后由 MHCⅠ类分子递呈

阶段：• 内源性 Ag肽的产生及转运• MHCⅠ类分子荷肽• 递呈给 CD8+T 细胞

MHCⅠ类途径

1 、内源性抗原肽的产生• Generation of endogenous antigenic peptide–内源性抗原泛素化–经蛋白酶体（ LMP ）降解为短肽

Crystal Structure Of The 20s ProteasomeFrom Yeast

View

End on

Degradation in the proteasome

These components are induced by IFN-γ and replace constitutive components to confer proteolytic properties

The components of the proteasome include MECL-1, LMP2, LMP7LMP2 & 7 encoded in the MHC

Proteasome cleaves proteins into hydrophobic and basic amino acids

Cytoplasmic cellular proteins, including non-self proteinsare degraded continuously by a multicatalytic protease of 28 subunits

2 、内源性抗原肽转运至内质网• Transportation of endogenous antigenic peptide into ER–经抗原加工相关转运体（ TAP ）转运至 ER

ER

CYTOSOL

Peptide antigens produced in the cytoplasm are physically separated from newly formed

MHC class I

Newly synthesisedMHC class I molecules

Peptides needaccess to the ER inorder to be loaded

onto MHC class I molecules

ER membrane

Lumen of ER

Cytosol

Transporters associated withantigen processing (TAP1 & 2)

Transporter has preference for 8-15 amino acid peptideswith hydrophobic, basic C termini

TAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-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

Hydrophobictransmembranedomain

Peptide antigensfrom proteasome

3、 MHCⅠ类分子荷肽• Peptide-loading of MHC class Ⅰ molecules–内质网内钙联蛋白、钙网蛋白协助下 MHCⅠ类分子合成–tapasin 协助下 MHCⅠ类分子与 TAP孔道内侧口结合–Ag 肽 -MHCⅠ类分子复合物形成

Endoplasmic reticulum

Calnexin bindsto nascentclass I chainuntil β2-M binds

TAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

β2-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

4、递呈给 CD8+T 细胞• Presentation of endogenous antigen–Ag 肽 -MHCⅠ类分子经高尔基体–通过胞吐作用表达于细胞表面–供 CD8 ＋T 细胞识别

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

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

Peptide

TAP-1 TAP-2

HSV protein blocks transportof viral peptides into ER

Sent to lysosomesfor degradation

Evasion of immunity by interference with endogenous antigen processing

Sent to lysosomes for degradation

Normally exported to the cell surface

Adenoviralproteinretains MHCclass I in the ER

Evasion of immunity by interference withendogenous antigen processing

三、非经典抗原加工递呈途径• Non classical pathway• 外源性抗原也可被 MHCⅠ类分子递呈

–外源性抗原穿透细胞膜进入胞浆–外源性抗原自内体逸出进入胞浆----以内源性抗原方式加工递呈给 CD8+T 细胞

• 内源性抗原也可被 MHCⅡ类分子递呈–胞质内蛋白形成自吞小泡，与内体 / 溶酶体融合 ----以外源性抗原方式加工递呈给 CD4+T 细胞

•交叉致敏（ cross-priming ）–专职性 APC 激活未致敏的肿瘤或病毒抗原特异性 CD8+T 细胞的机制– DC具有交叉致敏作用

学习了抗原提呈细胞的特性和功能后，你是如何体会抗原提呈细胞的免疫学功能和生物学意义的呢？