Binding of lipopolysaccharide and complexes of lipopolysaccharide to serum low density lipoproteins to liver macrophages

Abstract

Binding of [3H]-lipopolysaccharide toxin (LPS) and complexes of LPS with serum [125I]-labeled low density lipoproteins (LDL) with primary culture of rat liver macrophages (Kupffer cells) has been studied. Total, specific and nonspecific binding was determined. The receptor interaction was shown to dominate for both LPS and LDL-LPS complexes, amounting to 70-77% and 80-85%, respectively. The Scatchard plot was essentially non-linear for LPS binding but linear for LDL-LPS complexes. At the LPS Scatchard graph, however, two regions approximately fitting linear regression could be identified. Those regions correspond to two different types of specific binding sites: the first is for lower toxin concentrations of 0.25-0.50 microg/ml with K(d) = 0.75 microg/ml; while the second is for higher LPS concentrations of 7.5-15 microg/ml with K(d) = 5.39 microg/ml. For LDL-LPS complexes only K(d) equal to 2.80 microg/ml was ascertained. The LDL-LPS complexes significantly blocked the LPS binding (-40%) while acetylated or oxidized LDLs exerted a less pronounced effect. LPS inhibited binding of LDL-LPS complexes (-60%), while acetylated or oxidized LDLs suppressed interaction of LDL-LPS complexes with Kupffer cells insignificantly. It is suggested that, while binding to the Kupffer cell surface, a substantial portion of both LPS and LDL-LPS complexes share the same scavenger receptors with which however, modified LDLs interact weakly. The LDL-LPS complexes can interact, apart from receptors common with LPS, with other receptors exhibiting similar binding parameters, with the apo-B/E receptors playing an inessential role.