Decreased toxicity of polymorphonuclear neutrophils toward hepatocytes isolated from rats with acute inflammatory reaction. We have recently demonstrated that polymorphonuclear neutrophils were toxic to hepatocytes through a protease-mediated mechanism. Since synthesis of antiproteases is markedly increased during acute inflammatory reaction, the aim of this work was to investigate the toxicity of neutrophils against normal vs. inflammatory rat hepatocytes. Acute inflammatory reaction was induced by subcutaneous injection of turpentine 24 hr before the experiments. Hepatocytes from normal and turpentine-treated rats were isolated by collagenase digestion. They were incubated with human neutrophils stimulated by 1 mg/ml opsonized zymosan. Cytotoxicity was quantified by the percentage of alanine aminotransferase activity released by hepatocytes in culture medium after an 18-hr incubation period. By comparison to normal hepatocytes, inflammatory hepatocytes were more resistant to the toxicity of neutrophils. At a neutrophil/hepatocyte ratio of 20:1, the alanine aminotransferase activity releases were 53.7% +/- 5.4% (mean +/- 1 S.E.) and 27.4% +/- 4.8% for normal and inflammatory hepatocytes, respectively. Similarly, inflammatory hepatocytes were found to be less sensitive than normal hepatocytes to the toxic effect of purified neutrophil cathepsin G. In contrast, both types of hepatocytes exhibited the same sensitivity to H2O2 generated by a system consisting of glucose and glucose oxidase. Two arguments suggested that the resistance of inflammatory hepatocytes to protease toxicity was explained by an increased production of antiproteases by these cells: (a) when tested against cathepsin G and porcine pancreatic elastase activities, the protease inhibitory capacity of conditioned medium from inflammatory hepatocytes was higher than that of conditioned medium from normal hepatocytes; (b) conditioned medium from inflammatory hepatocytes markedly reduced the toxicity of stimulated neutrophils as that of cathepsin G. 