Altered and infected cells are eliminated by CD8+ cytotoxic T lymphocytes. This requires production of antigenic peptides mostly in the cytosol, transport to the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP), and cell surface presentation by major histocompatibility complex class I (MHC-I). Strikingly, antigen presentation occurs without TAP, although it is inefficient and associated to human pathology. TAP-independent peptides derive both from membrane and secreted proteins, as well as cytosolic ones. The efficiency of TAP-independent presentation may be impacted by the availability of receptive MHC-I, and in turn by the functional presence in the ER of the peptide-loading complex, itself anchored on TAP. Without TAP, surface expression of human leukocyte antigen (HLA)-B allotypes varies widely, with those presenting a broader peptide repertoire among the most TAP-independent. Much remains to be learned on the alternative cellular pathways for antigen presentation in the absence of TAP.

中文翻译：

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内源性 TAP 非依赖性 MHC-I 抗原呈递：不仅仅是 ER 腔。

改变和感染的细胞被 CD8+ 细胞毒性 T 淋巴细胞清除。这需要主要在细胞质中产生抗原肽，通过与抗原加工相关的转运蛋白 (TAP) 转运至内质网 (ER)，并通过主要组织相容性复合物 I 类 (MHC-I) 呈递细胞表面。引人注目的是，抗原呈递在没有 TAP 的情况下发生，尽管它效率低下并且与人类病理学有关。TAP 非依赖性肽来源于膜蛋白和分泌蛋白，以及胞质蛋白。不依赖于 TAP 的呈递效率可能受到接受性 MHC-I 的可用性的影响，进而受到肽负载复合物在 ER 中的功能存在的影响，该复合物本身锚定在 TAP 上。如果没有 TAP，人类白细胞抗原 (HLA)-B 同种异型的表面表达变化很大，那些在最不依赖 TAP 的情况下呈现更广泛的肽库。在没有 TAP 的情况下，关于抗原呈递的替代细胞途径仍有许多需要了解。