Liver regeneration and fibrosis after inflammation.

The liver is a unique organ with an extraordinary capacity to regenerate upon various injuries. In acute and transient liver injury by insults such as chemical hepatotoxins, the liver in rodents returns to the original architecture by proliferation and remodeling of the remaining cells within a week. In contrast, chronic liver inflammation due to various etiologies, e.g., virus infection and metabolic and immune disorders, results in liver fibrosis, often leading to cirrhosis and carcinogenesis. In both acute and chronic inflammation, a variety of immune and non-immune cells in the liver is involved in the processes resulting in either regeneration or fibrosis. In addition, chronic hepatitis often accompanies proliferation of atypical biliary cells, also known as liver progenitor cells or oval cells. Although the origin of liver progenitor cells and its contribution to hepatic repair is still under intense debate, recent studies have revealed a regulatory role for immune cells in progenitor proliferation and differentiation. In this review, we summarize recent studies on liver regeneration and fibrosis in the viewpoint of inflammation.