Inhibition of TNF-triggering activity of lipopolysaccharide by a proteinaceous factor from normal mouse liver extract

Recent studies have revealed that animals have evolved a wide range of protective systems against the deleterious effects of LPS, but the molecular mechanisms in the barrier functions of liver against enterobacterial LPS, particularly in mammals, are poorly understood. In this study, we extracted a soluble fraction from the liver of normal mice (normal liver extract, NLE) and examined its effect on biologic activities of LPS. Preincubation of NLE and LPS suppressed serum-dependent TNF induction (TNF-triggering activity) of LPS; the effect was dose-dependent and overcome by increasing LPS concentration, but treatment of macrophages with NLE showed no effect. Separation by ultrafiltration and protease sensitivity demonstrated that the factor(s) in NLE was a protein(s). We tentatively called this liver LPS-inactivating factor (LLIF). LPS inactivation by LLIF was temperature-dependent and required the coexistence of divalent cations. LLIF also suppressed a synthetic lipid A analogue, ONO-4007. Pretreatment of LPS with serum rendered LPS refractory to the action of LLIF. However, LLIF was unable to inhibit limulus amebocyte lysate activation by LPS. Direct interaction of LLIF and lipid A was evident by the method of [1-14C]ONO-4007 binding to solid-phase LLIF, but treatment of [1-14C]ONO-4007 with LLIF generated no degradative products. These results suggest that LLIF probably interacts with the lipid A portion of LPS and interferes with the association of LPS and LBP (LPS-binding protein) in serum, and that LLIF may be one of the protective molecules in liver against the gastrointestine-derived LPS.