Effect of Transgenic Overexpression of FLIP on Lymphocytes on Development and Resolution of Experimental Autoimmune Thyroiditis

In our previous studies, resolution of granulomatous experimental autoimmune thyroiditis (G-EAT) was promoted when thyroid epithelial cells were protected from Fas-mediated apoptosis due to transgenic overexpression of FLIP. We hypothesized that if FLIP were overexpressed on lymphocytes, CD4+ effector cells would be protected from Fas-mediated apoptosis, and resolution would be delayed. To test this hypothesis, we generated transgenic (Tg) mice overexpressing FLIP under the CD2 promoter. Transgenic FLIP was expressed on CD4+ and CD8+ T cells and B cells. Transgenic overexpression of FLIP protected cultured splenocytes from Fas-mediated, but not irradiation-induced, apoptosis in vitro. Unexpectedly, Tg+ donor cells transferred minimal G-EAT, which was partially overcome by depleting donor CD8+ T cells. When Tg+ and Tg− donors transferred equivalent disease, G-EAT resolution was delayed in FLIP transgenic mice. However, CD2-FLIP Tg+ donors often transferred less severe G-EAT, even after depletion of CD8+ T cells. This influenced the rate of G-EAT resolution, resulting in little difference in G-EAT resolution between groups. Tg+ mice always had reduced anti-mouse thyroglobulin autoantibody responses, compared with Tg− littermates, presumably because of FLIP overexpression on B cells. These results suggest that effects of transgenic FLIP on a particular autoimmune disease vary, depending on what cells express the transgene and whether those cells are effector cells or if they function to modulate disease.