Characterization of the human immune response to a polysaccharide vaccine from Pseudomonas aeruginosa

Sera from humans vaccinated with a high-molecular-weight polysaccharide vaccine to Pseudomonas aeruginosa immunotype 1 (IT-1) were analyzed for duration of the immune response, specificity for the IT-1 determinant, and by assessing the immunoglobulin classes elicited. The ability of purified IgG, IgM, and IgA to interact with peripheral blood leukocytes, as well as purified polymorphonuclear neutrophils or mononuclear cells, was also examined in an opsonophagocytosis assay. Levels of antibody to IT-1 remained significantly (P less than 0.001) elevated 21 months after immunization. Responses were generally specific to the IT-1 serotype determinant. Some vaccinees also responded to immunotype 2 and immunotype 5 determinants. IgG, IgM, and IgA serum antibodies were all elicited by vaccination. IgG and IgA were effective opsonins for P aeruginosa. IgM-mediated opsonophagocytosis required complement. Serum IgA was highly effective in conjunction with mononuclear cells in opsonophagocytosis of P aeruginosa, suggesting that these immune components may be capable of protecting neutropenic hosts.