Endothelial cells and macrophages are located within the hepatic sinusoids. These two cell types play an important role in the clearance of bacterially derived lipopolysaccharide from the portal circulation. Our laboratory has previously demonstrated that treatment of rats with lipopolysaccharide results in the accumulation of macrophages in the liver that display properties of activated mononuclear phagocytes. This study was designed to analyze the effects of lipopolysaccharide on hepatic endothelial cells. Female Sprague-Dawley rats were treated with 5 mg/kg of lipopolysaccharide. Macrophages and endothelial cells were isolated from the rats 48 hr later by in situ perfusion of the liver with collagenase and pronase followed by differential centrifugation and centrifugal elutriation. We found that lipopolysaccharide treatment of rats resulted in an increase in the number of both macrophages and endothelial cells recovered from the liver. Using specific monoclonal antibodies and flow cytometry, both macrophages and endothelial cells were found to express cell surface markers for Ia antigen, leukocyte common antigen, CD4 and the macrophage antigen, ED2. Macrophages expressed greater levels of these markers than endothelial cells. Flow cytometric analysis also revealed considerable subpopulation heterogeneity in the endothelial cells in antigen expression, physical characteristics and functional activity. Treatment of rats with lipopolysaccharide decreased expression of cell surface markers on the macrophages but not on the endothelial cells. This may be due to the distinct origin of these cells. To determine whether endothelial cells, like macrophages, were activated by lipopolysaccharide, we examined their ability to produce reactive oxygen intermediates.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 (IL-1) and interleukin-6 (IL-6) derived from Kupffer cells are major inducers of hepatic inflammation and the acute phase response. The present studies demonstrate that liver endothelial cells also produce significant quantities of IL-1 and IL-6, suggesting that these cells also participate in these processes. Endothelial cells and macrophages were isolated from female Sprague-Dawley rats by combined collagenase and pronase perfusion of the liver followed by centrifugal elutriation. In the absence of stimulation, endothelial cells were found to spontaneously produce IL-1 and IL-6 in a time-dependent manner, reaching maximal levels after 10 h in culture for IL-1 and 6-8 h for IL-6. The amount and kinetics of cytokine production by hepatic endothelial cells were similar to those observed with Kupffer cells. In further studies, the effects of lipopolysaccharide (LPS), a potent liver macrophage activator and inflammatory agent, on cytokine release were analyzed. Treatment of rats with LPS resulted in a decrease in IL-1 release by both cell types compared to cells from untreated animals. In contrast, LPS treatment had no major effect on IL-6 release. We also found that both macrophages and endothelial cells could be induced to produce additional IL-1 and IL-6 by treatment with LPS in vitro, but only if they were preincubated for at least 24 h prior to stimulation with LPS and analyzed for cytokine release. These data demonstrate that liver endothelial cells, like Kupffer cells, have the capacity to produce immunoregulatory and proinflammatory cytokines.

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