Considerable evidence suggests that monocytes/macrophages play a crucial role in the process of liver injury and repair. Recent investigations have focused on the function of various macrophage-produced cytokines in liver disease. Much is still unknown, however, about the mechanism of macrophage recruitment and activation during liver disease. To further define this process, the gene expression of the monocyte chemoattractant monocyte chemoattractant protein 1 (MCP-1) was examined in animal and human liver disease. MCP-1 mRNA was not found in normal rat liver by Northern blot analysis. After single-dose treatments with the hepatotoxins carbon tetrachloride and galactosamine, MCP-1 mRNA was detectable beginning at 2 and 4 h after treatment, respectively, and was expressed continuously until 60-72 h. During chronic carbon tetrachloride administration, MCP-1 mRNA levels were elevated for the entire 10 weeks of treatment with peak levels of expression occurring early (weeks 1-3) and late (weeks 8-10) in this model. Isolated liver cell fractions from rats treated for 3 weeks with carbon tetrachloride revealed the major cellular source of MCP-1 mRNA to be fat-storing or Ito cells, with some expression occurring in the endothelial cell fraction. Studies of potential inducers of hepatic MCP-1 expression showed that lipopolysaccharide, tumor necrosis factor-alpha, and interleukin-1 alpha and beta treatments all led to MCP-1 expression. Finally, studies of human liver samples revealed MCP-1 gene expression in nondiseased liver and greatly increased levels in livers from patients with fulminant hepatic failure. These data implicate MCP-1 from fat-storing cells as a modulator of the process of liver injury and further support a role for MCP-1 in the pathogenesis of human disease.