Up-regulation of interleukin-22 mediates liver fibrosis via activating hepatic stellate cells in patients with hepatitis C

•Up-regulation of IL-22 was positively associated with liver fibrosis severity.•Accumulated IL-22-positive cells could also be found in other chronic liver diseases.•IL-22 aggravated liver fibrosis progression by activating human stellate cells.•IL-22/IL-22R1 was involved in the pathogenesis of liver fibrosis in patients with HCV.

Interleukin-22 (IL-22) is known to play a critical role in liver immunity. However, the role of IL-22 in HCV-associated liver fibrosis is poorly understood. In this study, patients with HCV infection disclosed significant increases in peripheral numbers of IL-22-producing cells as well as in IL-22 plasma levels. In the liver, the increased intrahepatic IL-22+ cells were positively correlated with fibrotic staging scores and clinical progression from CHC to cirrhosis. Moreover, the majority of IL-22+ cells were located in fibrotic areas in the liver of patients with cirrhosis and co-localized with α-smooth muscle actin (α-SMA) positive hepatic stellate cells (HSCs). In vitro, administration of IL-22 was accompanied with inhibited LX-2 cell apoptosis, promoted LX-2 cell proliferation, increased expression of α-SMA, and up-regulated collagen production by LX-2 cells. Collectively, our data provide evidence that IL-22 may contribute to the fibrogenesis of HCV-associated liver fibrosis by activating HSCs.