Communications

Abstract The cell wall lipopolysaccharide (LPS) of Gram-negative bacteria possesses both endotoxic and O-antigenic activity. Recent electron microscopic studies have provided strong evidence that the LPS, localized in the outer membrane of the cell wall, may also serve as a substrate for the action of the complement (C′) enzymes. “Lesions” indicative of utilization of the terminal C′ components have been visualized on the surface of Gram-negative bacteria and on the membranous LPS after incubation with fresh mammalian serum (1–3). Since various biologically active factors are generated by C′ interactions prior to terminal component activation, it was suggested that certain of the biologic effects of LPS might be mediated via the C′ system (2, 4). An important contribution to the study of the chemical nature of endotoxin has recently been obtained by O. Lüderitz et al. (5). These workers found that endotoxin, isolated from a rough strain of Salmonella minnesota, consisted mainly of 2-keto-3 deoxyoctonate (KDO) and “lipid A” without O-polysaccharide or heptose.