LPS-binding protein circulates in association with apoB-containing lipoproteins and enhances endotoxin-LDL/VLDL interaction

LPS-binding protein (LBP) and serum lipoproteins cooperate in reducing the toxic properties of LPS. In the present study, we demonstrate that LBP circ ulates in association with LDL and VLDL in healthy persons. ApoB was found to account at least in part for the interaction of LBP with LDL and VLDL. A lthough LBP interacted with purified apoA-I in vitro, no association of LBP with apoA-I or HDL was found in serum. Consistent with the observed associ ation of LBP with LDL and VLDL, these lipoproteins also were demonstrated t o be the predominant I,PS-binding lipoproteins. Most interestingly, the ass ociation of LBP with LDL and VLDL strongly enhanced the capacity of these l ipoproteins to bind LPS. Because this function of LBP is of utmost importan ce during infection, the association of LBP and LPS with lipoproteins was a lso studied in serum from septic patients. In septic serum containing high LBP levels and a markedly altered lipoprotein spectrum, most of the LBP is associated with LDL and VLDL, although some LBP appeared to circulate free from lipoproteins. Also in this serum, LPS was found to bind predominantly to LDL and VLDL. The observed binding of LBP and LPS to LDL and VLDL, as we ll as the LBP-dependent incorporation of LPS into these lipoproteins, empha sizes a crucial role for circulating LBP-LDL/VLDL complexes in the scavengi ng of LPS.