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Type 1 diabetes is an autoimmune disorder, which occurs due to β cell damage. Interleukin (IL)-10, a pleotropic cytokine, has been reported to have anti-inflammatory, immunosuppressive and immunostimulatory properties. Administration of IL-10 is known to prevent autoimmune diabetes in non-obese diabetic (NOD) mice. However, the mechanism of IL-10-induced protection in NOD mice requires further investigation. The aim of the present study was to evaluate the protective effect of transgenic IL-10 expression in pancreatic β cells against autoimmune damage in NOD mice and to elucidate its mechanism of action. Female NOD mice (9 weeks old) were intraperitoneally injected with an adenovirus carrying either IL-10 (Adv-IL-10) or green fluorescent protein (Adv-GFP). Blood glucose was monitored weekly and the expression of IL-10 was evaluated using reverse transcription quantitative polymerase chain reaction. IL-10 and interferon (IFN)-γ expression levels in serum and splenocytes were analyzed. CD4+CD25+FoxP3+ T regulatory (Treg) cells were determined by flow cytometry. Apoptosis of pancreatic β cells was determined using a terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling assay and expression levels of Fas and caspase-3 were estimated by immunohistochemistry analysis. The results revealed that mice treated with IL-10 showed less severe insulitis and a lower incidence of diabetes compared with the saline control and Adv-GFP groups. In addition, compared with the control group, IFN-γ levels were decreased in sera and splenocytes, while IL-10 expression was increased in sera only. The number of CD4+CD25+FoxP3+ Treg cells was increased in IL-10-injected mice. Furthermore, the expression levels of Fas and caspase-3 were decreased in IL-10-injected mice compared with that of GFP-injected and control mice, which was concomitant with a reduction in β cell apoptosis. In conclusion, the present study demonstrated that IL-10 gene transfer reduced the expression of the inflammatory cytokines, attenuated pancreatic insulitis and inhibited β cell apoptosis. This therefore indicated that IL-10 reduced the incidence of diabetes in female NOD mice. [ABSTRACT FROM AUTHOR]