Caspi Rachel R
Laboratory of Immunology, National Eye Institute, NIH, Bethesda, MD 20893-1857, USA.
Immunol Rev. 2006 Oct;213:23-35. doi: 10.1111/j.1600-065X.2006.00439.x.
The eye is the prototypic immune-privileged organ. Its antigens were once believed to be expressed exclusively in the eye, which resides behind an efficient blood-organ barrier, and were believed to be unknown to the immune system. Self-tolerance to ocular components was therefore believed to be based not on immune tolerance but on immune ignorance. It is now known that the relationship between the immune system and the eye is much more complex. On the one hand, immune privilege is now known to involve not only sequestration but also active mechanisms that (i) inhibit innate and adaptive immune processes within the eye and (ii) shape the response that develops systemically to antigens released from the eye. On the other hand, retinal antigens are found in the thymus and have been shown to shape the eye-specific T-cell repertoire. However, thymic elimination of self-reactive T cells is incomplete, and such 'escapee' T cells are tolerized in the periphery as they recirculate through the body by encounter with self-antigen in healthy tissues. Due to the relative inaccessibility of the healthy eye to the immune system, peripheral tolerance mechanisms may not operate efficiently for ocular antigens, leaving a weak link in the homeostasis of tolerance. The case shall be made that although immune privilege protects vision by keeping the immune system at bay, a potential for developing destructive anti-retinal autoimmunity may be the price for the day-to-day protection afforded by immune privilege against inflammatory insults.
眼睛是典型的免疫赦免器官。其抗原曾被认为仅在眼睛中表达，眼睛位于有效的血 - 器官屏障之后，免疫系统对其抗原一无所知。因此，对眼部成分的自身耐受被认为不是基于免疫耐受，而是基于免疫忽视。现在已知免疫系统与眼睛之间的关系要复杂得多。一方面，现在已知免疫赦免不仅涉及隔离，还涉及主动机制，这些机制包括：（i）抑制眼内的先天性和适应性免疫过程；（ii）塑造全身对从眼睛释放的抗原产生的反应。另一方面，视网膜抗原在胸腺中被发现，并已被证明可塑造眼部特异性T细胞库。然而，胸腺对自身反应性T细胞的清除并不完全，这些“逃逸”的T细胞在通过健康组织中的自身抗原再循环时，会在周围组织中被耐受。由于健康眼睛相对不易被免疫系统接触到，外周耐受机制可能无法有效地作用于眼部抗原，从而在耐受的稳态中留下一个薄弱环节。尽管免疫赦免通过使免疫系统远离来保护视力，但发展为破坏性抗视网膜自身免疫的可能性可能是免疫赦免为抵御炎症损伤提供日常保护所付出的代价。
