MURINE IMMUNE-RESPONSES TO NEISSERIA-MENINGITIDIS GROUP-C CAPSULAR POLYSACCHARIDE AND A THYMUS-DEPENDENT TOXOID CONJUGATE VACCINE

The polysaccharide (PS) capsules of many pathogenic bacteria are poor immunogens in infants and young children as a result of the delayed re sponse to PS antigens during ontogeny. The development of polysacchari de-protein conjugate vaccines for Haemophilus influenzae type b, which have proven to be efficacious in this age group, has led to active de velopment by a number of investigators of conjugate vaccines for other diseases. We describe here the response of several mouse strains to t he capsular PS of Neisseria meningitidis group C (MCPS) conjugated to tetanus toroid (MCPS-TT) and the same response in BALB/c mice as a mod el of the immune consequences of conjugate vaccine immunization. The u se of a conjugate vaccine results in a shift in the isotype elicited i n response to the MCPS, from immunoglobulin M (IgM) and IgG3 to primar ily IgG1. A response to MCPS-TT is seen even among mouse strains which respond poorly to MCPS itself, emphasizing the importance of a strain survey when choosing a mouse model for a vaccine. The marked increase in IgG1 antibody titer was accompanied by a large increase in bacteri cidal activity of sera from these animals. Animals primed with the con jugate vaccine demonstrated a booster response after secondary immuniz ation with either the MCPS or the conjugate. The ability to produce a boosted IgG1 anti-MCPS response to the MCPS can be transferred to adop tive recipients by B cells alone from mice primed with MCPS-TT but not mice primed with MCPS alone. These data indicate that in BALB/c mice a single immunization with MCPS-TT is sufficient to induce a shift to IgG1 and generate a memory B-cell population that does not require T c ells for boosting.