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 2003 on three topics: (1) expression of surface molecules on lymphocytes that mediate ocular inflammation; (2) expression of retinal antigens in human thymi; (3) modulation of ocular inflammation by treatment with newly introduced immunoregulating compounds. Topic 1. T-lymphocytes are capable of invading non-lymphoid tissues and inducing inflammation only following activation. Our studies in FY 2002 demonstrated that expression of the chemokine receptor CXCR3 is upregulated on T-lymphocyte of type 1 ("Th1") following activation by exposure to their specific target antigen. Further analysis in FY 2003 of inflammation-inducing Th1 cells revealed, however, a complex pattern of expression of CXCR3. A sharp decline in the receptor expression was seen following re-activation of the Th1 cells in culture, a process that enhanced the pathogenic capacity of these cells when they are injected into recipient animals. Yet, CXCR3 was found to be involved in the actual invasion of the Th1 cells into the target organ, the eye, since this receptor was re-expressed on the injected Th1 cells while residing in the recipient animal, prior to their migration into the eye. Finally, CXCR3 expression was down-regulated once more on the Th1 cells, shortly after invading the eye, presumably due to re-exposure to the target antigen in the eye. These observations thus shed new light on the expression of CXCR3, a molecule that plays a major role in the process of immune-mediated inflammation. Topic 2. Autoimmune diseases are believed to be prevented in normal individuals by the deletion of lymphocytes with specificity against autologous antigens. This process, designated "central tolerance", is taking place in the thymus, where maturing lymphocytes are eliminated following exposure to the antigens they are specific against. Previous studies by our group have demonstrated the expression of retinal antigens in thymi of experimental animals. Further, these studies have established the relationship between thymic expression of retinal antigens and the resistance of the animal to uveitis induced by these antigens. This line of research was extended in FY 2003 to examine the expression in human thymi of five retinal antigens, known to induce uveitis in experimental animals. Samples of thymi were obtained from patients during surgery for congenital heart disease, after informed consent was obtained. Thymic expression of five retinal antigens was examined by the presence of the proteins' mRNA transcripts, using the RT-PCR method. Remarkable variabilities were observed among both the individual thymi and the retinal antigens. Transcripts of three retinal proteins, S-antigen (arrestin), recoverin and RPE65, were detected in almost all tested 18 thymic samples when examined after 37 or 40 cycles of PCR, whereas transcripts of interphotoreceptor retinoid-binding protein (IRBP) and rhodopsin were detected only in 6 or 7 of these samples. In addition, the former transcripts were detected in a few cases by 33 cycles of PCR, while IRBP and rhodopsin transcripts could not be found by the 33 cycles. These observations suggest that a variability exists among individuals in their thymic expression of autologous retinal antigens. Further, it is conceivable that these differences play a role in the susceptibility of individuals to autoimmune responses against retinal antigens. Topic 3. Two immunomodulating compounds, OCH and atorvastatin, were tested for their effect on immune-mediated ocular inflammation. 'OCH' is a synthetic analog of alpha-galactosylceramide, a natural stimulant for natural killer T (NKT) cells. NKT cells have the capacity to modulate the immune response and treatment with OCH was reported to inhibit the development of experimental autoimmune encephalomyelitis (EAE) and to induce a bias of NKT cells toward production of interleukin-4 (IL-4), a cytokine that can inhibit immunopathogenic processes. We tested the effect of OCH in a system in which T-helper lymphocytes of types 1 or 2 (Th1 or Th2) specific against hen egg lysozyme (HEL) induce inflammation in mouse eyes in which HEL is expressed. Treatment of recipient mice with OCH inhibited Th1-induced ocular inflammation, but slightly enhanced the disease induced by Th2 cells. In addition, treatment with OCH reduced the production of interferon gamma, but elevated the release of IL-4 by spleen cells of the recipient mice. Atorvastatin was recently reported to effectively inhibit the induction of EAE. Surprisingly, no inhibitory effect by the compound was observed when tested in the system of experimental autoimmune uveitis (EAU)