Thus, the observed increase of Th17 cells in our CHB patients may represent an HBV nonspecific phenomenon. Taken together, these results indicate that Th17 cells are closely associated with the superimposed liver damage induced by HBV infection. The precise mechanism of Th17 cells inducing liver damage in CHB patients remains unknown. The present study found Fer-1 in vitro that IL-17R was uniquely expressed on peripheral monocytes and mDCs in CHB patients. In addition, IL-17 in vitro can activate mDCs and monocytes and enhance their capacity to produce proinflammatory cytokines in a dose-dependent pattern. These proinflammatory cytokines

are critical for liver damage during hepatitis B progression.2 Indeed, our previous studies indicate that multiple immune cells, including mDCs, plasmacytoid DCs, and FoxP3-positive regulatory

T cells, can infiltrate the liver and actively participate in the immune-pathogenesis in mild and severe CHB patients.10–12 Thus, IL-17 can directly function on these IL-17R–expressing cells and exacerbate the inflammatory microenvironment of the liver. Notably, both mDCs and monocytes from CHB patients displayed lower levels of IL-17R expression and poorer responsiveness to IL-17 in vitro relative to those of HC subjects. This phenomenon can be explained by the negative feedback effects of high levels of IL-17 on the IL-17R–expressing cells because MK2206 IL-17 can significantly down-regulate IL-17R expression on these mDCs and monocytes (Supporting Fig. 3). Future studies should investigate the factors underlying the low responsiveness of mDCs and monocytes to IL-17 stimulation in vitro in CHB patients. Notably, a recent study indicated that hepatic stellate cells can also express

IL-17R; following IL-17 stimulation in vitro they can secret IL-8 and GRO-α and subsequently recruit neutrophils into the livers of patients with alcoholic liver disease.15 Therefore, it is necessary to understand whether IL-17 protein secreted by liver-infiltrating Th17 cells of CHB patients also enhances this chemokine production by liver parenchymal cells, which further recruit immune cells into the livers of CHB patients. Furthermore, we found that peripheral Th17 cells from CHB find more patients have little capacity to produce IL-22, a cytokine which has been shown to protect against T-cell hepatitis.32, 33 This loss of Th17-producing IL-22 might also exacerbate liver injury in CHB patients. Future studies should investigate whether these Th17 cells are inherently defective, or whether the CHB patients are simply lacking a cofactor for IL-22 production. Taken together, these data emphasize that liver Th17 cells may reinforce the pathogenic inflammatory microenvironment in the livers of CHB patients.