T cell effector mechanisms in experimental autoimmune uveitis (EAU).

Experimental autoimmune uveitis (EAU) is a T cell-mediated autoimmune model for posterior uveoretinitis in man. There is increasing evidence to suggest an important role for CD4+ T cells and their lymphokines in EAU induction, although the mechanisms involved are still not clear. Adoptive transfer of EAU in Lewis rats can be achieved using activated CD4^ T cell lines specific for retinal soluble antigen (S-Ag). However there is little information on the regulation of lymphokine expression by these uveitogenic T cell lines. In order to further understand the pathogenic mechanisms involved in EAU, S-Ag specific CD4+ T cell lines were established from Lewis rats immunized with S-Ag in CFA and were used to examine the regulation of lymphokine expression. Lymphokines present in the supernatant were assessed by bioassays and their mRNA was detected by polymerase chain reaction (PGR). All S-Ag specific cell lines established were found to be CD4+CD8-OX22'°" T cells. The mRNA samples were taken at 6 h and supernatant samples were taken at 24 h after stimulation. Results demonstrated that S-Ag specific T cell lines when stimulated with antigen express IL-2, IFN-y and IL-4 mRNA. Furthermore, IL-2 and IFN-y bioactivities correlated with gene expression of respective lymphokines except in one cell line which had no detectable IL-2. These findings suggest that the production of lL-2 and IFN-y may play important role in EAU induction. Furthermore, the time course data (3, 6, 24, 48 and 72h) with one of S-Ag specific T cell lines showed that the proliferation of murine HT-2 cells induced by the supernatant following ConA stimulation was only partially inhibited by rat IL-2R mAb, while proliferative response induced by supernatant after S-Ag activation could be totally blocked by rat IL-2R mAb, suggesting that there are HT-2 cell growth factors other than IL-2 in the supernatants following ConA, but not S-Ag stimulation. All these suggest that the way in which the T cell is activated has an effect on its resultant lymphokine secretion. Mouse CD4+ T cell clones have been divided into Thl and Th2 based on the patterns of lymphokines expressed, but in the rat there is still no evidence to support this. Rat CD4+ T cell clones specific for S-Ag or PPD established from antigen specific CD4+T cell lines were therefore examined for lymphokine expression. The results indicated that S-Ag specific CD4" ̂T cell clones exhibit mainly a Thl pattern but also a mixed (ThO) cytokine pattern on the basis of lymphokine mRNA expression, whereas the PPD specific CD4"*" T cell clones exhibit mostly a mixed (ThO) pattern but also Thl and Th2 cytokine patterns. In the rat, CD4+ T cells could be functionally divided into 0 X 2 2 ^ ' and 0X22^°^ subsets based on phenotypic expression of CD45 isoforms. It has been found that lymphokine expression by OX2 2 ^‘̂ h and 0X22*°'^ CD4^ T cells seems to correlate with that of murine CD4+ T cell clones. However, our results suggested that there is no simple correlation between rat CD4+ cell subsets (based on phenotypic expression of CD45 isoforms) and their lymphokine gene expression. Apart from inflammatory cytokines, immunosuppressive factors such as transforming growth factor-p (TGF-p) could play an important role in the down-regulation of EAU. To examine this further, the in vivo role of TGF-pl on the course of EAU was also examined. The results showed that intraocular TGF-pl had the effect of delaying the onset of EAU.