IL-10 impacts autoimmune diabetes via a CD8⁺ T cell pathway circumventing the requirement for CD4⁺ T and B lymphocytes

IL-10 is essential for an early phase of diabetes in nonobese diabetic (NOD) mice, but later becomes protective against its development. The mechanism by which IL-10 mediates the pathway to diabetes in these mice is unknown. Herein, we dissected the cellular and costimulation requirements for diabetes in transgenic (tg) NOD mice that expressed IL-10 in their pancreatic islets (IL-10-NOD mice). We found that IL-10 alone did not cause diabetes because the offspring (IL-10-NOD-scid mice) from backcrosses of IL-10-NOD mice with NOD-scid mice had no diabetes. Moreover, these IL-10-NOD-scid mice were free of lymphocytic infiltration. Treatment Of IL-10-NOD mice with depleting anti-CD4 mAb or control mAb had no effect on diabetes. Surprisingly, depletion of CD8⁺ T cells by treatment with the corresponding mAb inhibited diabetes without attenuating insulitis, demonstrating a critical role for CD8⁺ T cells in the disease process. Interestingly, B cell-deficient IL-10-NOD mice readily developed diabetes with kinetics and incidence Similar tO those observed in wild-type mice, demonstrating that B lymphocytes as APCs were not required in the disease process. Administration of anti-CD40 ligand (CD40L) mAb did not prevent disease, indicating that CD40/CD40L costimulation is not required for diabetes in IL-10-NOD mice. Immunization of IL-10-NOD mice with CFA or heat-shock protein 65, known to block diabetes in NOD mice, had no effect on their diabetes. We demonstrate that IL-10 contributes early to the pathology of diabetes via a CD8⁺ T cell pathway, eliminating the requirement for B lymphocytes and CD40-CD40L costimulation. Our findings provide a mechanism for the participation of IL- 10 in the early development of diabetes.