Ethanol changes sensitivity of Kupffer cells to endotoxin. Here, the hypothesis that interleukin-l receptor-associated kinase (IRAK), a downstream signaling molecule of toll-like receptors, regulates the response to LPS in Kupffer cells after ethanol treatment was evaluated. C57BL/6 mice were given ethanol intragastrically, and LPS was injected 1 or 21 h later. One hour after ethanol treatment, serum transaminases after LPS were 60% of control, while ethanol increased these parameters about 3-fold 21 h after ethanol. Pretreatment with antibiotics blocked these effects of ethanol. In Kupffer cells from mice treated with ethanol 1 h earlier, LPS-induced TNF alpha production, and IRAK expression and activity and NF kappaB were decreased 50-60% of control. In contrast, in Kupffer cells from mice treated with ethanol 21 h earlier, LPS-induced TNF alpha production, expression and activity of IRAK were increased 1.5-fold over controls, while NF kappaB was elevated S-fold. These data indicate that ethanol-induced tolerance and sensitization of Kupffer cells to endotoxin in mice involve IRAK.