TLR9-deficiency in B cells Promotes Immune Tolerance via IL-10 in a Type 1 Diabetes Mouse Model

Toll-like receptor 9 (TLR9) is highly expressed in B cells and B cells are important in the pathogenesis of type 1 diabetes (T1D) development. However, the intrinsic effect of TLR9 in B cells on beta cell autoimmunity is not known. To fill this knowledge gap, we generated non-obese diabetic (NOD) mice with a B cell-specific deficiency of TLR9 (TLR9^fl/fl/CD19-Cre+ NOD). The B cell-specific deletion of TLR9 resulted in near complete protection from T1D development. Diabetes protection was accompanied by an increased proportion of IL-10-producing B cells. We also found that TLR9-deficient B cells were hyporesponsive to both innate and adaptive immune-stimuli. This suggested that TLR9 in B cells modulates T1D susceptibility in NOD mice by changing the frequency and function of IL-10-producing B cells. Molecular analysis revealed a network of TLR9 with MMPs, TIMP1 and CD40, all of which are inter-connected with IL-10. Our study has highlighted an important connection of an innate immune molecule in B cells to the immuno-pathogenesis of T1D. Thus, targeting the TLR9 pathway, specifically in B cells, may provide a novel therapeutic strategy for T1D treatment.