Endogenous Toll-like Receptor 2 Modulates Th1/Treg-Promoting Dendritic Cells in Mice Corneal Transplantation Model

Purpose: Endogenous toll-like receptor (TLR) 2 is linked to allograft rejection in corneal transplantation. TLR2 also could modulate dendritic cell (DC) phenotype, resulting in T cell polarization. Thus, we investigated the role of endogenous TLR2 on DC development and T cell polarization during corneal rejection. Materials and Methods: Corneas of BALB/c mice were transplanted into the eyes of C57BL/6 wild-type (WT) recipients and TLR2(-/-) (KO) recipients. Graft survival and TLR2 mRNA expression were assessed. At day 14 after transplantation, to study endogenous TLR2 effects on DC development and function, surface expression of MHC classII (MHCII), CD86, CD80 and CD40 in ipsilateral cervical draining lymph nodes (DLNs) is measured by flow cytometry, and DC phenotype in corneas is detected by immunofluorescence. The levels of IL-12, IL-10 and IL-4 in corneas were measured by real time-qPCR (RT-qPCR). The ability of DCs to stimulate T cell polarization was assessed by IFN-gamma expressions via RT-qPCR and immunohistochemistry. Results: TLR2 mRNA expression in corneas was peaked at day 14 post-transplantation in WT group. KO group improved corneal allograft survival compared to the WT group. In addition, the KO group decreased expression of CD86, CD80 and CD40 on DCs compared to the WT group. There was no difference in MHCII expression in two groups. The CD11c(+)MHCII(+)CD40(high) DCs could not be detected in corneas of the KO group. Moreover, the KO group decreased IL-12 (Th1-promoting cytokines) mRNA expression and increasing IL-10 (Treg-promoting cytokines) mRNA expression compared to the WT group. IL-4 (Th2-promoting cytokines) mRNA expression gained no difference between the two groups. The IFN-gamma (Th1 cytokines) expression was significantly decreased in the KO group compared to the WT group. Conclusions: Endogenous TLR2 may contribute to allogeneic corneal rejection via Th1 immunity by activating Th1-promoting DCs and suppressing Treg-promoting DCs.