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Type 1 diabetes is an immune-mediated disease, in which T cells of the adaptive immune system mediate beta cell destruction. Recently the innate immune system has been linked to etiopathogenesis of several autoimmune diseases including type 1 diabetes, as innate effector cells (e.g. dendritic cells, monocytes/macrophages and NK cells) can prime and promote or regulate (auto)immune responses. We have previously developed an experimental autoimmune diabetes (EAD) model with insulin peptide B:9-23 immunization in transgenic H-2dmice expressing the costimulatory molecule B7.1 in their islets (under the Rat Insulin Promotor, RIP). We compared the induction of diabetes with polyinosinic–polycytidylic acid (Poly I:C), a mimic of double stranded viral RNA versus insulin B:9-23 peptide in mice following backcrossing of the B7.1 transgene on to BALB/c mice from original B7.1 C57Bl/6 mice. We find that diabetes induction by Poly I:C is C57Bl/6 associated, whereas B:9-23 peptide induced diabetes and induction of insulin autoantibodies (IAA) are dependent on BALB/c genes. This B:9-23 peptide induced diabetes is consistent with MHC class II H-2dbeing necessary for the response to this peptide. Of note Poly I:C induction of diabetes was lost while B:9-23 induction was retained with backcrossing to BALB/c mice. Interaction of genes and environment (antigenic epitope and viral mimic) can be important in the pathogenesis of immune mediated diabetes and activation of the innate immune system (e.g. Poly I:C) may be one key determinant. [Copyright &y& Elsevier]