Transforming Growth Factor-β and Natural Killer T-Cells Are Involved in the Protective Effect of a Bacterial Extract on Type 1 Diabetes

Abstract

The onset of type 1 diabetes in NOD mice is delayed by oral administration of a bacterial extract (OM-85) and can be completely prevented by its intraperitoneal administration. Optimal prevention is observed when starting treatment at 3 or 6 weeks of age, and some effect is still observed with treatment at 10 weeks of age. Using genetically deficient mice and cytokine-neutralizing monoclonal antibodies, we demonstrate here that the therapeutic effect does not involve T-helper type 2 cytokines (interleukin [IL]-4 and -10) but is tightly dependent on transforming growth factor (TGF)-β. Natural killer T-cells also participate in the therapeutic effect because CD1d^−/− NOD mice are partially resistant to the protective effect of OM-85. The question remains of the specificity of the protective effect of OM-85, which may include proinflammatory components. It will thus be important to further characterize the molecular components that afford protection from type 1 diabetes. Lipopolysaccharide is excluded, but other Toll-like receptor (TLR) agonists could be involved because OM-85 stimulated dendritic cells and induced TGF-β production by splenocytes in a TLR-2–, TLR-4–, and MyD88-dependent fashion.