TLR5 signaling enhances the proliferation of human allogeneic CD40-activated B cell induced CD4hiCD25+ regulatory T cells.

Although diverse functions of different toll-like receptors (TLR) on human natural regulatory T cells have been demonstrated recently, the role of TLR-related signals on human induced regulatory T cells remain elusive. Previously our group developed an ex vivo high-efficient system in generating human alloantigen-specific CD4(hi)CD25(+) regulatory T cells from naïve CD4(+)CD25(-) T cells using allogeneic CD40-activated B cells as stimulators. In this study, we investigated the role of TLR5-related signals on the generation and function of these novel CD4(hi)CD25(+) regulatory T cells. It was found that induced CD4(hi)CD25(+) regulatory T cells expressed an up-regulated level of TLR5 compared to their precursors. The blockade of TLR5 using anti-TLR5 antibodies during the co-culture decreased CD4(hi)CD25(+) regulatory T cells proliferation by induction of S phase arrest. The S phase arrest was associated with reduced ERK1/2 phosphorylation. However, TLR5 blockade did not decrease the CTLA-4, GITR and FOXP3 expressions, and the suppressive function of CD4(hi)CD25(+) regulatory T cells. In conclusion, we discovered a novel function of TLR5-related signaling in enhancing the proliferation of CD4(hi)CD25(+) regulatory T cells by promoting S phase progress but not involved in the suppressive function of human CD40-activated B cell-induced CD4(hi)CD25(+) regulatory T cells, suggesting a novel role of TLR5-related signals in the generation of induced regulatory T cells.