β-cell destruction in NOD mice correlates with Fas (CD95) expression on β-cells and proinflammatory cytokine expression in islets

A mechanism of autoimmune destruction of islet beta-cells in type 1 diabetes has been proposed to be the binding of Fas ligand (FasL) on T-cells to Pns receptors on beta-cells, We investigated this proposal by examining the expression of Fast and Fas on islet-infiltrating T-cells and beta-cells in relation to beta-cell destruction in a syngeneic islet transplant model In NOD mice. Diabetic NOD mice were transplanted with syngeneic islets and injected with complete Freund's adjuvant, which prevented diabetes recurrence (nondestructive insulitis), and with phosphate-buffered saline, which did not(beta-cell destructive insulitis), Two-color immunohistochemical assays revealed that Fast was expressed on CD4(+) T-cells, CD8(+) T-cells, and beta-cells in islet grafts from both diabetic and normoglycemic mice, and the percentage of each type of cell that expressed Fast was greater in islet grafts from normoglycemic compared with diabetic mice, In contrast, Fas was expressed on CD4(+) T-cells, CD8(+) T-cells, and beta-cells in islet grafts from diabetic mice, but it was nearly or totally absent on these cells in islet grafts from normoglycemic mice. Similarly, polymerase chain reaction analysis of islet grafts revealed that Fas mRNA expression was significantly lower in islet grafts from normoglycemic compared with diabetic mice. Also, mRNA levels of interleukin (IL)-1 alpha tumor necrosis fatter (TNF)-alpha, and interferon (IFN)-gamma were significantly lower in islet grafts from normoglycemic mice. Finally Fas was induced on NOD islet cells by incubation with IL-1 beta, IFN-gamma, and the combination of IL-1 beta, TNF-alpha, and IFN-gamma, These findings support the concept that cytokine-induced Fas receptor expression on islet beta-cells is a mechanism for their destruction by Fast-expressing CD4(+) and CD8(+) T-cells and, possibly by Fast-expressing beta-cells themselves.