Detection and Specificity of Lipid A Antibodies Using Liposomes Sensitized with Lipid A and Bacterial Lipopolysaccharides

Previous reports have shown that liposomal model membranes are appropriate objects for investigating the molecular basis of complement‐dependent membrane damage. The present study describes a different application for liposomes: their usefulness in screening sera suspected of containing antibodies against potential lipid antigens. Liposomes, actively sensitized with untreated or alkali‐treated lipid A derived from Salmonella minnesota , were found to release trapped glucose marker when incubated with a source of unheated complement and the antilipid A serum whose preparation is described in the preceding paper [1]. In the presence of complement, the anti‐lipid A serum could also promote loss of glucose from liposomes which had been actively sensitized with various untreated and alkali‐treated S or R form S. minnesota lipopolysaccharides. In contrast, several different anti‐R‐form sera had little effect on liposomes sensitized with either untreated or alkali‐treated lipid A. These results are in agreement with observations on the immunological specificity of lipid‐A antibodies using complement‐dependent hemolysis of passively sensitized human erythrocytes as test system. Alkali‐treated, but not untreated, lipid A could also be employed for passive sensitization of liposomes; in this regard, lipid A behaves similarly to S and R form lipopolysaccharides.