Recent papers have shown that the initial event in the pathogenesis of autoimmune type 1 diabetes (T1D) comprises sensing of molecular patterns released from apoptotic β-cells by innate immune receptors such as toll-like receptor (TLR). We have reported that apoptotic β-cells undergoing secondary necrosis called 'late apoptotic' β-cells stimulate dendritic cells (DCs) and induce diabetogenic T cell priming through TLR2. The role of other innate immune receptors such as TLR7 or TLR9 in the initiation of T1D has also been suggested. We hypothesized that TLR2 blockade could inhibit T1D at the initial step of T1D. Indeed, when a TLR2 agonist, Pam3CSK4 was administered chronically, the development of T1D in nonobese diabetic (NOD) mice was inhibited. Diabetogenic T cell priming by DCs was attenuated by chronic treatment with Pam3CSK4, indicating DC tolerance. For the treatment of established T1D, immune tolerance alone is not enough because β-cell mass is critically reduced. We employed TLR2 tolerance in conjunction with islet transplantation, which led to reversal of newly established T1D. Dipeptidyl peptidase 4 (DPP4) inhibitors are a new class of anti-diabetic agents that have beneficial effects on β-cells. We investigated whether a combination of DPP4 inhibition and TLR2 tolerization could reverse newly established T1D without islet transplantation. We could achieve normoglycemia by TLR2 tolerization in combination with DPP4 inhibition but not by TLR2 tolerization or DPP4 inhibition alone. β-cell mass was significantly increased by combined treatment with TLR2 tolerization and DPP4 inhibition. These results suggest the possibility that a novel strategy of TLR tolerization will be available for the inhibition or treatment of established T1D when combined with measures increasing critically reduced β-cell mass of T1D patients such as DPP4 inhibition or stem cell technology.
Keywords: Type 1 diabetes, Autoimmunity, TLR2, Tolerance, DPP4