AIMS/HYPOTHESIS: Disruption of the interferon-gamma (IFN-gamma) signalling pathway at the level of interferon regulatory factor-1 (IRF-1) protects islets against cytokine-induced nitric oxide production and cell death in vitro. The aim of this study was to investigate the effects of a global disruption of IFN-gamma signalling, or a selective disruption of IRF-1, on beta-cell sensitivity to in vivo immune destruction. METHODS: In a first set of experiments, IFN-gamma receptor knockout mice (IFN-gammaR-/-) and interferon regulatory factor-1 knockout mice (IRF-1-/-) were rendered diabetic by injections of 50 mg streptozotocin i. p. on 5 consecutive days (MLDSTZ). RESULTS: Whereas no difference in sensitivity to MLDSTZ-induced diabetes could be observed between IFN-gammaR-/- mice and their 129/Sv/Ev controls (50% vs 55%, NS), there was an increased incidence of diabetes in IRF-1-/- mice (100% vs 67% in C57B1/6 mice, p < 0.05). A similar increased sensitivity to immune destruction of IRF-1-/- islets was observed when these islets were used as allografts. Islet graft survival rate of IFN-gammaR-/- and 129/Sv/Ev islets, when transplanted in alloxan-diabetic BALB/c recipients, was comparable (12.0 +/- 1.9 days vs 12.9 +/- 2.3 days, NS). Allograft rejection, however, of IRF-1-/- islets by BALB/c recipients occurred more rapidly than following transplantation to their C57B1/6 controls (9.1 +/- 2.0 days vs 13.1 +/- 1.5 days, p < 0.003). CONCLUSIONS/INTERPRETATION: These data indicate that IFN-gamma signal transduction at the beta-cell level is not essential for immune beta-cell destruction in vivo. Moreover, disruption of the IRF-1 gene in pancreatic islets increases susceptibility to beta-cell killing, suggesting that IRF-1 might be necessary for the expression of putative beta-cell "defence and/or repair" genes.