抗原呈現

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(重定向自抗原呈遞
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抗原呈現(Antigen presentation)是免疫系統相當重要的一個機制。由於免疫細胞沒辦法「看見」細胞內部有沒有被細菌或是病毒感染,因此他們需要靠細胞透過主要组织相容性复合体(MHC)將細胞內部的物質碎片呈現於細胞表面,以利於免疫細胞辨識。另外,由於有些抗原體实在大到免疫細胞無法辨識,需靠其他吞噬細胞消化後經由抗原呈現回報給免疫細胞,呈現的細胞便稱為抗原呈現細胞(APCs)。

因为病原体可以进入身体的细胞内,这是很难从外部识别的,细胞毒性T细胞在体内运行核细胞常规分子健康筛选程序,以确保它们没有从细胞内的疾病,因此适合于使用。最常见的病毒可以在宿主细胞内进行复制;备选地细胞内细菌能够存活或癌基因可以被翻译成致瘤基因产物。为了便于筛选出这类细胞内的健康问题,在宿主细胞自愿提供其对细胞的细胞毒性T细胞的胞质外含量的比特期间定期访问检查。要做到这一点,所述宿主细胞通过一个专门的酶复合物,蛋白酶体,主要作用是降解细胞不需要的或受到损伤的蛋白质蛋白。MHC-1存在內質網中,當胞內抗原蛋白質經過LMP2/7的切割後,穿過內質網上的TAP tranporter,此抗原片段將與MHC-1的α1-α2結合,被送到此受感染的細胞表面進行抗原呈現給毒殺型T細胞。

CD8 +细胞毒性T细胞被编程以识别的肽联接到上所有有核细胞的MHC-I类分子。细胞毒性T细胞(也称为TC,杀伤T细胞或细胞毒性T淋巴细胞(CTL))是T细胞被专门用于诱导其他细胞死亡的入口。通过I类被CTL识别的抗原肽的导致杀伤靶细胞,其可通过病毒,卵胞浆内细菌感染,或者其他损坏或不正常的。另一方面,从生理蛋白质周转在健康细胞的耐受性的肽将被忽略。通过在病变细胞诱导的细胞毒性,细胞毒性T细胞确保身体保持健康;所消除的细胞可以通过健康细胞分裂新细胞所取代。

胞外抗原:第二類抗原呈現[编辑]

Dendritic cells (DCs) phagocytose exogenous pathogens such as bacteria, parasites, and toxins in the tissues and then migrate, via chemotactic signals, to T cell-enriched lymph nodes. During migration, DCs undergo a process of maturation in which they lose phagocytic capacity and develop an increased ability to communicate with T-cells in the lymph nodes. This maturation process is dependent on signaling from other pathogen-associated molecular pattern (PAMP) molecules through pattern recognition receptors, such as the members of the Toll-like receptor family.

The DC uses lysosome-associated enzymes to digest pathogen-associated proteins into smaller peptides. In the lymph node, the DC will display these antigenic peptides on its surface by coupling them to MHC Class II molecules. This MHC:antigen complex is then recognized by T cells passing through the lymph node. Exogenous antigens are usually displayed on MHC Class II molecules, which interact with CD4+ helper T cells. CD4+ lymphocytes, or TH, are immune response mediators, and play an important role in establishing and maximizing the capabilities of the adaptive immune response.

Expression of Class II is more restricted than Class I. High levels of Class II are found on dendritic cells, but can also be observed on activated macrophages, B cells, and several other host cell types in inflammatory conditions.

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