Immune Responses To Ocular Antigens

National Eye Institute

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Abstract

Targeted at learning about inflammatory eye diseases, this project focused in 2005 on three topics: (1) triggering of pathogenic autoimmune processes by microbial products; (2) active participation of antigen-nonspecific lymphoid cells in immune mediated inflammation; (3) suppression of immune-mediated ocular inflammation by curcumin, a food additive. Topic 1. Microbial products are assumed to play a major role in triggering autoimmune processes responsible for diseases such as multiple sclerosis, rheumatoid arthritis or intraocular conditions grouped under the term ?uveitis?. Little is known, however, about the molecular and cellular mechanisms that are involved in these pathogenic processes. In a study initiated in FY 2004 we set up an experimental system to investigate the capacity of microbe-derived molecules to trigger pathogenic autoimmune processes. In this system, naive lymphocytes specific against hen egg lysozyme (HEL) are adoptively transferred into recipient mice transgenically expressing HEL in their eyes. Ocular inflammation develops in the recipient mice only when the transferred cells become activated, in vivo, and, therefore, the experimental system makes it possible to examine the capacity of agents to trigger pathogenic autoimmunity. The microbial products tested in this study included seven molecules that are known to function as ?Toll-like receptor (TLR)? ligands, namely, molecules that bind to TLRs on antigen presenting cells and stimulate these cells to efficiently activate lymphocytes. Seven microbial products were tested, peptidoglycan, lipoteichoic acid, poly(I:C), that mimics viral RNA, lipopolysaccharide, flagellin, zymosan A, the bacterial oligodeoxynucleotide ?CpG?, and pertussis toxin. Recipient mice treated with any of the seven microbial products developed ocular inflammation, a finding that supports the notion that microbial infection plays a major role in initiating pathogenic autoimmunity. In addition, we found that pertussis toxin surpassed by far the other six tested microbial molecules in triggering severe ocular changes in recipient mice. This observation is currently under further investigation. Topic 2. The pathogenic process of tissue-specific autoimmune disease depends to a large extent on recruitment of antigen-nonspecific cells into the target tissue. Little is known, however, about the recruitment process and the features that characterize the recruited cells. The recruitment of antigen-nonspecific lymphoid cells into an inflammatory site was analyzed by using the experimental system of adoptively transferred ocular inflammation, in which lymphocytes specific against HEL, stimulated in vitro, induced inflammatory changes in eyes of recipient mice expressing HEL in their eyes. The transferred cells were recognized in this system by a specific ?clonotypic? antibody. A sharp increase in number of host lymphoid cells was seen in the spleen of injected recipient mice and many of these cells also exhibited cell surface markers that characterize ?tissue-invading? lymphocytes. The injected donor cells were the first to invade the recipient mouse eyes, but shortly thereafter, host cells also entered the affected eyes and rapidly became the large majority of infiltrating cells. Interestingly, eye infiltrating host cells also resembled donor cells in the affected eye, by acquiring a profile of surface markers that characterizes ?activated? lymphocytes. These results thus show that antigen-nonspecific lymphoid cells are actively involved in the process of immune-mediated inflammation. Topic3. Curcumin, a natural product that is the active component of the food additive turmeric, has been shown to exhibit anti-inflammatory activity. The potential capacity of curcumin in inhibiting immune-mediated ocular inflammation was tested by injecting the compound to mice developing experimental autoimmune uveitis (EAU), an animal model for intra-ocular inflammation. Treatment with curcumin inhibited the development of EAU, as well as the cellular immune response against the retinal antigen that was used for the disease induction. These findings thus suggest that curcumin could be considered in treatment and/or prevention of inflammatory eye disease.