Infiltration of Tr17 cells into ankle joints after onset of CIA through high expression of CCR6
To evaluate the characteristics of Tr17 cells, we analyzed draining LN cells harvested from C57BL/6 mice at days 10, 42, and 56 after 1st-CII immunization, and ankle joint (AJ) cells also harvested after arthritis development. Tr17 cells appeared in LN following CII immunization and increased in the ankle joints compared to LN (Figure 2a, b). Next, we wanted to investigate how Tr17 cells accumulate in inflamed joints after the onset of CIA. A previous study reported that CC chemokine receptor 6 (CCR6) expression contributed to the recruitment of arthritogenic Th17 cells to the inflamed joints9; therefore, we examined the expression of CCR6 in Tr17 cells. FACS analysis revealed that CCR6 expression cells was significantly up-regulated in Tr17 cells compared to not only RORγt-negative Treg cells but also RORγt-positive Th17 cells (Figure 2c). Interestingly, when compared to Foxp3wtRORγtfl/fl control mice, expression of CCR6 was significantly down-regulated in the Foxp3-positive Treg cells but not the Foxp3-netgative T cells of Foxp3creRORγtfl/fl cKO mice (Supplementary Figure 1), suggesting that infiltration of Treg cells to inflamed joints might be impaired in Foxp3creRORγtfl/fl cKO mice. These findings indicate that joint infiltration of Tr17 cells might contribute to the regulation of CIA prolongation through increased expression of CCR6.