Bacterial lipopolysaccharide (LPS)-specific antibodies in commercial human immunoglobulin preparations: superior antibody content of an IgM-enriched product

The anti-LPS antibody content of commercial intravenous immunoglobulins was examined by quantitative ELISA using LPS preparations from Escherichia coli, Klebsiella and Pseudomonas aeruginosa O serotypes occurring most frequently in Gram-negative septicaemia. Three IgG products from different manufacturers and one IgM-enriched product were tested. Mean antibody levels were significantly higher in the IgM fraction of the IgM-enriched product compared with ‘pure’ IgG products, indicating that natural antibodies against bacterial LPS belong primarily to the IgM class. Immunoblotting studies showed that antibody specificities were directed mainly against O side chain epitopes. Antibodies against rough mutant LPS representing various chemotypes were detected in IgG but not in IgM products. The virtual absence of antibodies against Vibrio cholerae LPS indicated that human anti-LPS antibodies result from continuous environmental exposure to Gram-negative pathogens. These data support the further development of IgM-enriched preparations for prophylaxis and treatment of Gram-negative nosocomial infections.