Adhesions of leukocytes to hepatocytes and sinusoidal endothelial cells mediates the induction and progression of hepatic injury. However, in contrast to endothelial cells, information regarding the regulation of interactions between leukocytes and hepatocytes is limited. In the present study, we investigated the effect of inflammatory mediators including lipopolysaccharide (LPS), staphylococcal enterotoxin B (SEB), interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) on the adhesion of polymorphonuclear leukocytes or lymphocytes to primary cultured rat hepatocytes, and on the expression of intercellular adhesion molecule-1 (ICAM-1) gene in hepatocytes. Both polymorphonuclear leukocyte and lymphocyte adhesion to hepatocytes were enhanced after exposure of hepatocytes to IFN-gamma and TNF-alpha, but not after exposure to LPS, SEB or IL-1beta. The adhesion induced by either IFN-gamma or TNF-alpha was inhibited by monoclonal antibodies against ICAM-1 or lymphocyte function-associated antigen-1 (LFA-1). Nonstimulated hepatocytes expressed faintly ICAM-1 mRNA, which increased slightly during the culture period. ICAM-1 mRNA expression was up-regulated to a greater extent by incubating hepatocytes with IFN-gamma or TNF-alpha, and peaked after 12 hr of incubation with TNF-alpha and after 24 hr with IFN-gamma. These results indicate that IFN-gamma and TNF-alpha induce the expression of ICAM-1 on parenchymal hepatocytes and that the LFA-1-ICAM-1 pathway plays an important role in the interaction between hepatocytes and neutrophils or lymphocytes.