【每天学点细胞治疗20】人体免疫细胞是如何识别抗原的呢
人体免疫细胞如何识别抗原的呢？
How do T-cells recognize antigens？
T细胞如何识别抗原？
T lymphocytes cannot directly recognize or be activated by antigens on microbes or those that are extra-cellular in circulation.
T淋巴细胞不能直接被微生物或保外循环物识别或激活。
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.
他们通过抗原呈递细胞APCs（b淋巴细胞、巨噬细胞、树突细胞或其他有核细胞）程序呈递给他们识别。
Very specifically, T-cells require peptides that are derived from these antigens to be presented along with certain cell surface molecules called MHC molecules.
具体来说，T细胞接受抗原的多肽和MHC细胞表面分子的呈递。
MHC: major histocompatibility complex
主要组织相容性复合体
T-lymphocyte possesses a T cell receptor(TCR) made of an αβ polypepitide chain，which recognizes peptides displayed by the MHC molecule.
T淋巴细胞具有一个T细胞受体由αβ多肽链构成，识别MHC多肽组合。
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细胞还拥有T细胞活化信号转导所必需的其他蛋白质和协同受体。
CD4 and CD8 molecules are co-receptors present on CD4+ and CD8+ T cells, respectively.
CD4和CD8分子是分别存在于CD4+和CD8+ T细胞上的协同受体。
These co-receptors bind to the MHC molecule during antigen recognition and are necessary for T-cell activation.
这些协同受体在抗原识别过程中与MHC分子结合，是T细胞活化所必需的。
CD3 complex are a bunch of lolypeptides that help in transduction of signals for T-cell activation.
CD3复合物是一组多肽，有助于T细胞活化的信号转导。
CD28 is a co-receptor that bind to a B7 molecule present on the nucleated or an antigen presenting cell.
CD28是一种协同受体，其与存在于有核细胞或抗原呈递细胞上的B7分子结合。
MHC genes
MHC molecules are proteins encoded by MHC genes located in the short arm of chromosome6.
MHC分子是由位于染色体6短臂的MHC基因编码的蛋白质。
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种类型的MHC分子MHC I、II、III，其中I和II对于T细胞的抗原识别是重要的。
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.
事实上，它们是抗原呈递细胞或有核细胞表面供T细胞识别多肽。
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.
内源性抗原(病毒或肿瘤抗原)被细胞内的蛋白体分解成肽，并被运输到内质网。
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.
在这里，MHC I分子捕获肽，然后被运输到质膜，在那里它将肽展示在细胞表面，为识别做准备。
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.
肽结合的MHC I分子被CD8+ T细胞识别，TCR与肽相互作用，CD8辅受体与MHC I分子结合。
CD8+ T cells are MHC class I restricted and can recognize peptides only bound with MHC I molecule.
CD8+ T细胞受MHC I类限制，只能识别与MHC I分子结合的肽。
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如树突状细胞或噬细胞捕获的外源性抗原,在溶酶体中进行蛋白水解降解，并且分解的肽与II类MHC结合。
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.
与肽结合的MHC II被转运到细胞表面，随后被CD4+T细胞识别——与肽和CD4辅受体相互作用的TCR与MHC II分子结合。
CD4+T cells are MHC class II restricted and can recognise peptides only bound with MHC II molecule.
CD4+T细胞受MHC II类限制，只能识别与MHC II分子结合的肽。
