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Beta-cell destruction in NOD mice correlates with Fas (CD95) expression on beta-cells and proinflammatory cytokine
W Suarez-Pinzon1, O Sorensen, R C Bleackley
1Department of Medicine, University of Alberta, Edmonton, Canada.
Abstract:
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 Fas receptors on beta-cells. We investigated this proposal by examining the expression of FasL 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 FasL 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 FasL 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)-1alpha, tumor necrosis factor (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-1beta, IFN-gamma, and the combination of IL-1beta, 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 FasL-expressing CD4+ and CD8+ T-cells and, possibly, by FasL-expressing beta-cells themselves.
Insights
Fas receptor expression on beta-cells, induced by cytokines, leads to their destruction by T-cells in type 1 diabetes. This mechanism involves Fas ligand binding to Fas receptors on beta-cells.
Area of Science:
- Immunology
- Endocrinology
- Cell Biology
Background:
- Type 1 diabetes involves autoimmune destruction of insulin-producing beta-cells.
- Fas ligand (FasL) on T-cells binding to Fas receptors on beta-cells is a proposed mechanism for beta-cell death.
Purpose of the Study:
- To investigate the role of FasL and Fas expression in autoimmune beta-cell destruction in type 1 diabetes.
- To examine the relationship between Fas/FasL expression, insulitis, and beta-cell destruction in a NOD mouse model.
Main Methods:
- Utilized a syngeneic islet transplant model in NOD mice.
- Employed two-color immunohistochemistry to detect FasL and Fas expression on immune cells and beta-cells.
- Performed polymerase chain reaction (PCR) to analyze mRNA levels of Fas and key cytokines (IL-1α, TNF-α, IFN-γ).
Main Results:
- FasL was expressed on T-cells and beta-cells in both diabetic and normoglycemic mice, with higher expression in normoglycemic mice.
- Fas expression was significantly higher on T-cells and beta-cells in diabetic mice compared to normoglycemic mice.
- Cytokine mRNA levels (IL-1α, TNF-α, IFN-γ) were lower in non-destructive insulitis models. Fas expression on beta-cells was induced by cytokines like IL-1β and IFN-γ.
Conclusions:
- Cytokine-induced Fas receptor expression on islet beta-cells is a key mechanism for their destruction in type 1 diabetes.
- Both CD4+ and CD8+ T-cells expressing FasL, and potentially FasL-expressing beta-cells themselves, contribute to beta-cell demise.