Accumulation of Activated Mononuclear Phagocytes in the Liver Following Lipopolysaccharide Treatment of Rats

Abstract

Lipopolysaccharide (LPS) is a toxic bacterial cell wall component that is rapidly cleared from the portal circulation by Kupffer cells. To determine if interaction with LPS causes the accumulation and activation of mononuclear phagocytes (MNP) in the liver, we compared the morphological and functional characteristics of MNP obtained from livers of rats treated with LPS (5 mg/kg, intravenously [IV]) with normal resident Kupffer cells. MNP were isolated from rat livers by combined collagenase/pronase perfusion, selective digestion, and differential centrifugation on a metrizamide gradient. MNP obtained from livers of LPS-treated rats were found to display morphologic and functional characteristics of activated macrophages. These cells were generally larger than resident cells, were highly vacuolated, and adhered to culture dishes more rapidly. Both cell types phagocytized sheep red blood cells (sRBC) in a time-dependent manner, reaching a maxium after 60–75 min incubation with sRBC. However, MNP from livers of LPS-treated rats phagocytized 10–15 times more sRBC than resident Kupffer cells from untreated animals. Employing the Boyden chamber technique, both cell types were also found to be chemotactic to a number of stimuli including the complement fragment, C5a, the tumor promoter, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), and collagenous peptides related to tissue breakdown products. MNP from livers of LPS-treated rats were generally 10–15 times more responsive to the chemoattractants than resident Kupffer cells. In addition, both resident Kupffer cells and MNP from LPS-treated rats were found to release superoxide anion in response to stimulation by C5a and TPA. Taken together these results suggest that LPS treatment of rats leads to the recruitment and activation of MNP in the liver.