Increased Th17 cells are accompanied by FoxP3(+) Treg cell accumulation and correlated with psoriasis disease severity.

Both T-helper 17 cells (Th17) and CD4(+)CD25(+) regulatory T cells (Treg) play important roles in the pathogenesis of psoriasis. However, the relationship between Th17 and Treg cells and their dynamic variations in psoriasis remain unclear. In this study, we found that both Th17 and FoxP3(+) Treg cells were increased in psoriasis patients both in the peripheral circulation and skin tissue lesions and were positively correlated with disease severity. The ratio of Th17 to Treg cells in skin tissue lesions was inversely correlated with PASI scores, while it was positively correlated with PASI scores in the circulation. IL-17 secretion by CD4(+) T cells was not regulated by Treg cells, even though Treg cells exhibited significant inhibition on CD4(+) T cells proliferation and IFN-gamma production. These findings provide new information regarding the association between Th17 and Treg cells, which will further our understanding of the pathogenesis of psoriasis.