Previous studies have shown that hepatocellular function is significantly depressed early during sepsis and that this is associated with a marked increase in the circulating levels of the hepatocellular stimulatory factor (IL-6). It remains unknown, however, whether or not Kupffer cells (KC) are activated during sepsis and whether these cells are the major contributors to the increased circulating levels of this cytokine. The objectives of this study were, therefore, to determine whether or not during sepsis: (1) KC are stimulated in vivo to release IL-6, as compared to other cytokines; (2) KC differ from splenic macrophages (SMφ) in their ability to release cytokines; and (3) there is a difference in macrophage (Mφ) cytokine release between endotoxin (ET)-tolerant (C3H/HeJ) and ET-intolerant (C3H/HeN) mice. To assess this, KC and SMφ were harvested at 1 or 24 hr from mice which had been subjected to polymicrobial sepsis by cecal ligation and puncture (CLP) or sham-operation. Following depletion of the nonadherent cells, KC and SMμ cultures were incubated for 24 hr in the presence or absence of 10 μg of ET/ml, and the levels of interleukin (IL)-1, IL-6, and TNF release were determined by bioassays. Sepsis induced an early (at 1 hr) in vivo stimulation of KC but not SMφ IL-6 release, irrespective of ET-tolerance/intolerance. However, the release of IL-1 or TNF was not markedly different for either CLP or sham KC. KC harvested from mice 24 hr post-CLP no longer showed an increase in innate cytokine release, whereas SMφ from these same animals exhibited a marked reduction in cytokine release both in the presence and in the absence of added ET. These findings support the notion that during early sepsis KC are selectively activated to release IL-6, irrespective of the animals' sensitivity to ET. Furthermore, the enhanced localized release of IL-6 by KC induced by CLP may contribute to hepatocellular dysfunction observed during early sepsis. © 1992.