Both CD4(+)and CD8(+)T cells are required for IFN-gamma gene expression in pancreatic islets and autoimmune diabetes development in biobreeding rats

To study the relative roles of CD4(+)and CD8(+)T cells and their cytokine products in autoimmune diabetes development, we selectively depleted CD4(+)and CD8(+)T cells in autoimmune diabetes-prone (DP) biobreeding (BB) rats, by administrations of anti-CD2 and anti-CD8 monoclonal antibody (mAb) respectively. We then analysed cytokine mRNA expression, by PCR assay, in mononuclear leukocytes isolated from islets and spleens of control and mAb-treated DP-BB rats. Depletion of CD4(+)T cells (by anti-CD2 mAb) in blood, spleen and islets prevented diabetes development in DP-BB rats, and depletion of CD8(+)T cells (by anti-CD8 mAb) delayed and significantly decreased diabetes incidence. Depletion of either CD4(+)or CD8(+)T cells completely prevented IFN-gamma mRNA upregulation in islets of DP-BB rats above the low level expressed in islets of diabetes-resistant (DR) BB rats. Also, IL-10 mRNA levels in islets of DP-BB rats were significantly decreased by depletion of either CD4(+)or CD8(+)T cells, whereas the effects of the anti-T cell mAb on mRNA levels of other cytokines in islets (IL-2, IL-4, IL-12p40, and TNF-alpha) were discordant. In contrast, both mAb treatments significantly upregulated IL-4 and TNF-alpha mRNA levels in spleens of DP-BB rats. These results demonstrate that islet infiltration by both CD4(+)and CD8(+)T cells is required for IFN-gamma and IL-10 production in islets and beta-cell destruction. Depletion of either CD4(+)or CD8(+)T cells may prevent beta-cell destruction by decreasing IFN-gamma and IL-10 production in islets and increasing IL-4 and TNF-alpha production systemically.