人體免疫細胞如何識別抗原的呢？

How do T-cells recognize antigens？

T細胞如何識別抗原？

T lymphocytes cannot directly recognize or be activated by antigens on microbes or those that are extra-cellular in circulation.

T淋巴細胞不能直接被微生物或保外循環(huán)物識別或激活。

They are rather programmed to be able to recognize antigens that are presented to it by antigen presenting cells(APCs) like B lymphocytes, macrophages, dendritic cells or other nucleated cells.

他們通過抗原呈遞細胞APCs（b淋巴細胞、巨噬細胞、樹突細胞或其他有核細胞）程序呈遞給他們識別。

Very specifically, T-cells require peptides that are derived from these antigens to be presented along with certain cell surface molecules called MHC molecules.

具體來說，T細胞接受抗原的多肽和MHC細胞表面分子的呈遞。

MHC: major histocompatibility complex

主要組織相容性復合體

T-lymphocyte possesses a T cell receptor(TCR) made of an αβ polypepitide chain，which recognizes peptides displayed by the MHC molecule.

T淋巴細胞具有一個T細胞受體由αβ多肽鏈構(gòu)成，識別MHC多肽組合。

Apart from the TCR, T cells also possess other proteins and co-receptors that are necessary for signal transduction for T-cell activation.

除了TCR，T細胞還擁有T細胞活化信號轉(zhuǎn)導所必需的其他蛋白質(zhì)和協(xié)同受體。

CD4 and CD8 molecules are co-receptors present on CD4+ and CD8+ T cells, respectively.

CD4和CD8分子是分別存在于CD4+和CD8+ T細胞上的協(xié)同受體。

These co-receptors bind to the MHC molecule during antigen recognition and are necessary for T-cell activation.

這些協(xié)同受體在抗原識別過程中與MHC分子結(jié)合，是T細胞活化所必需的。

CD3 complex are a bunch of lolypeptides that help in transduction of signals for T-cell activation.

CD3復合物是一組多肽，有助于T細胞活化的信號轉(zhuǎn)導。

CD28 is a co-receptor that bind to a B7 molecule present on the nucleated or an antigen presenting cell.

CD28是一種協(xié)同受體，其與存在于有核細胞或抗原呈遞細胞上的B7分子結(jié)合。

MHC genes

MHC molecules are proteins encoded by MHC genes located in the short arm of chromosome6.

MHC分子是由位于染色體6短臂的MHC基因編碼的蛋白質(zhì)。

There are 3 types of MHC molecules MHC I,II,III out of which I and II are important for antigen recognition by T-cells.

有3種類型的MHC分子MHC I、II、III，其中I和II對于T細胞的抗原識別是重要的。

MHC I:A+CB

MHC II:DR+DQ+DP

In fact, their function is to display peptides on the cell surface of an antigen presenting cell or a nucleated cell, for the purpose of recognition by T-cells.

事實上，它們是抗原呈遞細胞或有核細胞表面供T細胞識別多肽。

MHC I ,cell, CD8

Now an endogenous antigen like a virus or a tumor antigen is broken down into peptides by proteosomes inside the cell and are transported to the endoplasmic reticulum.

內(nèi)源性抗原(病毒或腫瘤抗原)被細胞內(nèi)的蛋白體分解成肽，并被運輸?shù)?/span>內(nèi)質(zhì)網(wǎng)。

Here, the MHC I molecule captures the peptide, and is then transported to the plasma membrane where it displays the peptide on the cell surface，ready for recognition.

在這里，MHC I分子捕獲肽，然后被運輸?shù)劫|(zhì)膜，在那里它將肽展示在細胞表面，為識別做準備。

Peptide bound MHC I molecule is recognized by a CD8+ T cell and the TCR interacting with the peptide and the CD8 co-receptor binding with the MHC I molecule.

肽結(jié)合的MHC I分子被CD8+ T細胞識別，TCR與肽相互作用，CD8輔受體與MHC I分子結(jié)合。

CD8+ T cells are MHC class I restricted and can recognize peptides only bound with MHC I molecule.

CD8+ T細胞受MHC I類限制，只能識別與MHC I分子結(jié)合的肽。

MHC II, APC, CD4

An exogenous antigen, captured by an APC like a dendritic cell or a mocrophage undergoes proteolytic degradation in lysosomes, and the broken down peptides bind to class II MHC in the lysosome.

被APC如樹突狀細胞或噬細胞捕獲的外源性抗原,在溶酶體中進行蛋白水解降解，并且分解的肽與II類MHC結(jié)合。

The peptide bound MHC II is transported to the cell surface，and is subsequently recognised by a CD4+T cell ---- the TCR interactin gwith the peptide and the CD4 co-receptor binding with the MHC II molecule.

與肽結(jié)合的MHC II被轉(zhuǎn)運到細胞表面，隨后被CD4+T細胞識別——與肽和CD4輔受體相互作用的TCR與MHC II分子結(jié)合。

CD4+T cells are MHC class II restricted and can recognise peptides only bound with MHC II molecule.

CD4+T細胞受MHC II類限制，只能識別與MHC II分子結(jié)合的肽。