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Previous reports have shown that liposomal model membranes are appropriate objects for investigating the molecular basis for 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 anti-lipid A serum whose preparation is described in the preceding paper [1]. In the presence of complements, 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 from 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, bu 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. [ABSTRACT FROM AUTHOR]

From E. coli 0100:K?(B):H2 a lipopolysaccharide and an acidic polysaccharide were extracted with saline. The lipopolysaccharide was purified by repeated ultracentrifugation and the acidic polysaccharide by fractional precipitation with cetavlon. Both substances contained rhamnose, galactose, glucosamine, glycerol, and phosphate. The lipopolysaccharide was degraded in 1% acetic acid at 100° and the degraded polysaccharide was fractionated on Sephadex G-50. Thus a fraction was obtained which represents the specific polysaccharide moiety of the lipopolysaccharide. comparison of this fraction with the acidic polysaccharide (chemical analysis, periodate oxidation, alkaline hydrolysis, partial acid hydrolysis) showed that both substances have not only the same composition (rhamnose, galactose, glucosamine, glycerol and phosphate in the molar ratios of 2:1:1:1:1) but also the same structure. Both substances consist of a main chain (composed of rhamnose, galactose and glucosamine) to which glycerol is bound via a phosphodiester bridge from one of its primary hydroxyl groups to one of the rhamnose residues. Some alternatives for the structure are presented. In serological tests (passive haemagglutination, bacterial agglutination, immune precipitation and inhibition of these) it was shown that acidic polysaccharide and lipopolysaccharide have identical reactivities in anti-O and anti-OK antisera. This confirms the structural identity of the polysaccharides. It is concluded that E. coli 0100:K?(B):H2 contains no polysaccharide which represents a K antigen. The O antigen of this strain contains glycerol phosphate as (part of) a determinant group. Precipitating antibodies, directed against this group are present in anti-OK antiserum and not in anti-O antiserum. In this context the phenomenon of O inagglutinability of E. coli atrains, which carry K antigens, is discussed. Possible implications in the definition of K antigens of the B type in human enteropathogenic E. coli strains are presented. [ABSTRACT FROM AUTHOR]