Anti-idiotype induced protection against Neisseria meningitidis serogroup C bacteremia.

We have developed a monoclonal anti-idiotypic antibody, designated 6F9, which acts as the surrogate image of the meningococcal group C capsular polysaccharide (MCP). Murine immunization with 6F9 results in a T-dependent anti-MCP antibody response. To examine the protective nature of the antibody response elicited by 6F9 we performed a series of live challenge studies using a murine model for meningococcal infection in which mice were iron dextran treated and challenged with 10 x LD50 of meningococcal group C strain 35E. Adult BALB/c mice immunized with 6F9 had a 100% survival and a significantly reduced level of bacteremia at 24 h. Mice immunized with MCP had an 80% survival rate, all survivors were bacteremic at 24 h. Neonatal mice primed within 24 h of birth and immunized at 4 weeks of age with 6F9 had a 100% survival and cleared their bacteremia by 8 h, which was significantly faster than the MCP primed and immunized mice. Neonatal mice primed with 6F9 and challenged at 5 weeks of age had a survival rate of 90% which was significantly higher than mice primed with MCP and the control group (60% and 50% survival, respectively). Mice primed at birth and immunized at 8 days had a 100% survival and 90% of these mice had sterile blood cultures by 8 h. Mice primed and immunized with MCP all remained bacteremic at 24 h. These data indicate that the anti-Id 6F9 which mimics the capsular polysaccharide of group C meningococci is capable of inducing protective immunity in immunologically mature as well as immature animals.