Endotoxin-neutralizingprotein (ENP) of the horseshoe crab isoneof themost potent neutralizersof endotoxins [bacterial lipopolysaccharide (LPS)]. Here, we report on the inter-action of LPS with recombinant ENP using a variety of physical and biological techniques. In biological assays (Limulusamebocyte lysate and tumour necrosis factor-a induction in human mononuclear cells), ENP causes a strong reduction of the immunostimulatory ability of LPS in a dose-dependent manner. Concomitantly, the accessible negative surface charges of LPS and lipid A (zeta potential) are neutralized and even converted into positive values. .
