Recent experimental data suggest that the idiosyncratic nature of drug-induced liver disease (DILD) may be due in part to a deficiency of one or more hepatoprotective factors. In this study we have investigated whether interleukin (IL)-6 may also be one of these factors. Following the induction of liver injury with acetaminophen (APAP), a time-dependent increase in liver mRNA expression of IL-6 and its family members IL-11, leukemia inhibitory factor, and oncostatin M was observed in wild type (WT) mice, suggesting a possible hepatoprotective role played by this cytokine family. Indeed, mice lacking IL-6 (IL-6(-/-)) were more susceptible than were WT mice to APAP-induced liver injury. The increased susceptibility of the IL-6(-/-) mice was associated with a deficiency in the expression of hepatic heat shock protein (HSP)25, 32, and 40 as well as inducible HSP70 following APAP treatment. These results suggest that IL-6 and possibly other family members may protect the liver from injury, at least in part, by up-regulating the hepatic expression of several cytoprotective HSPs. (C) 2003 Elsevier Science (USA). All rights reserved.