Multidose Streptozotocin Induction of Diabetes in BALB/cBy Mice Induces a T Cell Proliferation Defect in Thymocytes Which Is Reversible by Interleukin-4

Thymic T cell function in streptozotocin-treated (STZ) diabetic mice has been examined. STZ administration suppresses thymic T cell proliferation in response to mitogen stimulationin vitro.Secretion of IL-4 was dramatically reduced; however, secretion of IL-2 or IFN-γ was not significantly inhibited. RT-PCR analysis of thymocyte RNA revealed that levels of IL-4 mRNA were dramatically decreased in STZ-treated mice. Levels of mRNA encoding IFN-γ were similar, but the appearance was delayed in thymocytes derived from STZ-treated mice, implying differential regulation of IL-4 and IFN-γ. Defective thymocyte proliferation was partially restored by exposure to IL-2in vitro;however, IL-4 completely reversed the STZ-induced defect. Administrationin vivoof IL-4 before STZ treatment reversed the STZ-induced thymocyte proliferation defect and prevented both pancreatic islet destruction and hyperglycemia. Thymocyte cell surface differentiation markers were not appreciably different from control mice. Collectively these experiments suggest that STZ treatment of mice reduces expression of IL-4 which is associated with development of autoimmune diabetes.