Preparation and Characterization of a Nontoxic Polysaccharide-protein Conjugate That Induces Active Immunity and Passively Protective Antibody Against Pseudomonas Aeruginosa Immunotype 1 in Mice

Acid treatment of Pseudomonas aeruginosa immunotype 1 lipopolysaccharide generated a low-molecular-weight polysaccharide fraction that was detectable in agar gel immunodiffusion but did not induce antibodies or resistance to infection in mice. The polysaccharide was treated with periodate to generate additional aldehyde groups. Oxidized polysaccharide was covalently coupled by reductive amination to 1,4-diaminobutyl-derivatized bovine serum albumin. Physical properties of the conjugate were characterized by gel filtration and high-pressure liquid chromatography. The gelation activity of the conjugate in the Limulus amoebocyte lysate assay was 4,000-fold less than native lipopolysaccharide by weight. Mice immunized with the conjugate resisted challenge with P. aeruginosa immunotype 1 that killed 90% of mice immunized with saline. Immunization with the conjugate vaccine induced humoral immunoglobulin G that passively protected normal and burned mice. These results indicate that conjugation of nonimmunogenic polysaccharide antigen of P. aeruginosa restores immunogenicity similar to that of native lipopolysaccharide without restoring endotoxicity inherent in lipopolysaccharide.