Induction in mice of cell-mediated immunity to Pseudomonas aeruginosa by high molecular weight polysaccharide and vinblastine

The effect of the cytotoxic drug vinblastine on the development of immunity to high m.w. polysaccharide (PS) isolated from culture supernates of Pseudomonas aeruginosa was investigated. One microgram of PS, a normally nonimmunogenic, nonprotective dose, plus 75 μg of vinblastine were administered to BALB/c mice, and afforded protection to live organism challenge with the homologous strain. The kinetics and serotype specificity of the immune response indicated an active immunization had occurred. Analyses of serum antibody levels of mice given the PS-drug regimen in a sensitive, radioactive antigen-binding assay (RABA) failed to show development of antibody to the immunizing PS. Immunity could be passively transferred with spleen cells but not by serum from PS-drug-immunized animals, and the effector cell was removed by antisera to the Thy-1.2 antigen. Nu/nu mice were also protected against challenge after immunization with PS and vinblastine, but this protection was observed in association with the development of serum antibody to PS in these mice, as measured in the RABA. Protective immunity could not be elicited in the BALB/c mice by PS plus cyclophosphamide. These data suggest that under certain conditions, PS antigens can elicit T cell-dependent immune phenomena, and this T cell-dependent immunity can protect mice from live organism challenge against an extracellular bacterial pathogen.