Treatment of autoimmune diabetes by inhibiting the initial event

Abstract

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: Autoimmunity; DPP4; TLR2; Tolerance; Type 1 diabetes.

Figure 1

TLR2 tolerance induced by prolonged treatment with Pam3CSK₄ in vivo. (A) When CD4⁺ diabetogenic T cells from BDC2.5/NOD mice were labeled with carboxyfluorescein succinimidyl ester (CFSE) and transferred into control recipient NOD mice, CD4⁺ T cell proliferation measured by analyzing CFSE dilution by FACS analysis gated on CD4⁺ and Vβ4⁺ cells was observed specifically in the pancreatic lymph nodes but not in the mesenteric lymph nodes, as previously reported (16). In NOD mice treated with Pam3CSK₄ in vivo for 3 weeks, CD4⁺ diabetogenic T cell proliferation was significantly attenuated, indicating DC tolerance. Pooled results (right). A representative histogram (left). (B) Splenocytes prepared from NOD mice to which Pam3CSK₄ was administered for 3 weeks, were further treated with Pam3CSK₄ (black line) or PBS (gray filled histogram) in vitro for 1 day. The induction of costimulatory molecules on DCs by in vitro treatment with Pam3CSK₄ that was determined by FACS analysis gated on CD11c⁺ cells was significantly lower compared to control NOD mice, suggesting DC tolerance. Fold changes of mean fluorescent intensities (MFI) (lower). (C) No significant difference in the expression of costimulatory molecules on splenic DCs between NOD mice that were treated with Pam3CSK₄ in vivo (black line) and control NOD mice (gray line), suggests that in vivo Pam3CSK₄ treatment for 3 weeks does not activate DCs. (^***p<0.005; ^*p<0.05; ns, not significant) (Originally published in The Journal of Immunology. Kim D. H., J-C. Lee, S. Kim S, S. H. Oh, M.-K. Lee, K.-W. Kim, M.-S. Lee. 2011. Inhibition of autoimmune diabetes by TLR2 tolerance. J. Immunol.187: 5211-5220. Copyright © [2011] The American Association of Immunologists, Inc.)

Figure 2

Effect of in vivo treatment with Pam3CSK₄ on diabetes transfer by sensitized diabetogenic T cells. The incidence of diabetes after adoptive transfer (AT) of splenocytes from diabetic NOD mice to irradiated nondiabetic recipient NOD mice was significantly reduced by treatment of the recipient NOD mice with Pam3CSK₄ for 2 weeks before AT (p<0.005). (Originally published in The Journal of Immunology. Kim D. H., J-C. Lee, S. Kim S, S. H. Oh, M.-K. Lee, K.-W. Kim, M.-S. Lee. 2011. Inhibition of autoimmune diabetes by TLR2 tolerance. J. Immunol.187: 5211-5220. Copyright © [2011] The American Association of Immunologists, Inc.)