Immune Responses To Ocular Antigens

National Eye Institute

Investigators

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Abstract

Targeted at learning about inflammatory eye diseases, this project focused in 2004 on three topics: (1) modulation of ocular inflammation by natural killer T (NKT) cells; (2) mechanisms and molecules that trigger or modulate pathogenic autoimmunity; (3) profiles of molecules expressed in eyes with inflammation induced by different mechanisms. Topic 1. NKT cells exert immunomodulating capacities, mainly following activation by glycolipids such as alpha-galactosylceramide (a-GalCer). In our previous studies, reported in FY 2003, we found that "OCH", an analog of a-GalCer, inhibits the induction of ocular inflammation by adoptively transferred T-helper type 1 (Th1) cells, but enhances disease induced by Th2 cells. OCH stimulates selectively the production of the Th2-specific cytokine interleukin (IL)?4 by NKT cells and its effects on the ocular inflammation was attributed to this activity. This assumption was tested in FY 2004 by comparing OCH with another analog of a-GalCer, designated a-C-GC, that stimulates specifically the production of a Th1-specific cytokine, interferon gamma, by the NKT cells (Schmieg et al., J. Exp. Med. 198:1631, 2003). Surprisingly, despite their different patterns of cytokine stimulation, a-C-GC resembled OCH in inhibiting ocular inflammation by Th1 cells but slightly enhancing disease induced by Th2 cells. These observations thus indicate that the effect of a-GalCer and its analogs is not necessarily related to their capacity to stimulate cytokine production by NKT cells. These data are of particular interest since these NKT-stimulating molecules are being considered as potential immunomodulators in humans. Topic 2. Surprisingly, little is known about the mechanisms that trigger most autoimmune diseases. Healthy individuals harbor lymphocytes that recognize tissue-specific self antigens but remain at a "naive" stage and do not initiate any immunopathogenicity. It is generally assumed that these lymphocytes may acquire pathogenic capacity, following activation due to infection and/or trauma. We examined experimentally this notion in a system in which naive T-cells specific against a foreign antigen are adoptively transferred into recipient Tg mice that express this antigen in their eyes. Inflammation developed only in eyes of recipient mice that were also treated by injection with bacterial oligonucleotides (ODN). This observation thus supports the notion that autoimmunity may be triggered by microbial products. Other ODNs, on the other hand, have been found to be suppressive to the pathogenic immune response and capable of inhibiting immune-mediated ocular inflammation. These latter observations suggest that suppressive ODN could be considered for treatment of immune-mediated inflammation in humans. Topic 3. Experimental autoimmune uveitis (EAU), an animal disease that serves as a model for intraocular inflammation ("uveitis") in humans, is initiated by T-cells specific against ocular antigens, following the engagement of their receptors with these target antigens. The ensuing pathogenic process is mediated by a chain of events that is triggered by cytokines made by the T-cells and encompasses several other inflammation-related molecules. We have found that ocular inflammation could also be induced by local expression of two interleukins (IL), IL-1 and IL-7; transgenic mice expressing these IL's in their eyes developed severe ocular inflammation. A comparison between the gene expression profile of molecules in mouse eyes with inflammation due to engagement of T-cell receptor (as in EAU), or the local expression of IL-1 or IL-7 showed upregulation of the same molecules, but with remarkable variations among the three eye diseases in their expression of the individual molecules. The data thus suggest that inflammatory reactions triggered by different mechanisms use the same battery of inflammatory-related molecules, but with considerable variations.