The effect of lipopolysaccharide (LPS) on the expression of CD95 (APO-1/Fas) receptor and ligand (CD95L) was studied in primary cultures of rat liver Kupffer cells (KCs), sinusoidal endothelial cells (SECs), and parenchymal cells (PCs) at the messenger RNA (mRNA) level and by means of immunocytochemistry. LPS treatment of KCs and SECs led to a three- to five-fold increase in CD95L mRNA levels within 6 hours, which declined thereafter. Within 24 hours, the number of KCs and SECs staining positive for CD95L strongly increased. After a lag phase of 12 hours after LPS addition, in both cell types the mRNA levels for the soluble CD95 isoform increased approximately 10-fold; however, the number of KCs and SECs staining positive for transmembrane CD95 remained low and did not significantly increase. Compared with nonparenchymal cells, CD95L mRNA levels in primary hepatocyte cultures were low in the absence and presence of LPS. On the other hand, functionally active CD95 expression markedly increased in response to LPS in these cells. Dexamethasone diminished the LPS-induced stimulation of CD95L expression in nonparenchymal cells but markedly stimulated CD95L expression in PCs. Apoptosis of PCs and thymic lymphocytes was stimulated by the addition of supernatants derived from LPS-treated KC or SEC cultures and was apparently mediated by CD95L as assessed by its sensitivity to inhibitors of the CD95-dependent apoptotic pathway in PCs. The data suggest a complex and timely coordinated interplay between the various liver cell populations with respect to LPS-induced activation of the apoptotic machinery with potential relevance for immunoregulation.