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To investigate the role of Kupffer cells in complement activation, we used a rat model of acute hepatic injury induced by D-Galactosamine (GalN) and lipopolysaccharide (LPS). In in vivo study, minimal histological changes were observed after i.p. GalN (200 mg/kg) single administration. Complement hemolytic activity (CH 50) decreased to 70% of its initial value 2-3 h after i.p. LPS (1.5 mg/kg) single administration. Massive hepatic necrosis was induced by simultaneous administration of GalN and LPS. After 2-3 h, CH 50 decreased to 70% of its initial value, and deposition of C3 fluorescence (C3) was observed in Kupffer cells. After 4 h, GPT was greatly increased (1286 +/- 240 IU/l), CH 50 was further reduced, and C3 was observed on hepatocyte membranes and in the cytosol. In in vitro study, we used hepatocyte cultures and co-cultures of hepatocytes and Kupffer cells to investigate the participation of GalN, LPS, complement, and Kupffer cells in hepatic cell necrosis. We found no increase of LDH (% leakage) when LPS and complement were added to the medium (22.7 +/- 5.7%). A moderate increase was observed with the addition of GalN (33.2 +/- 2.6%). A remarkable increase was observed only with the addition of GalN, LPS, and complement to the co-culture (50.0 +/- 8.8%). These results suggest that Kupffer cells activated by LPS are very important in promoting acute hepatic injury by complement.