A potential polyvalent Neisseria meningitidis vaccine based on a mixture of CaCl2 cell extracts from groups A, B and Y.

Outer membrane proteins (OMP) from Neisseria meningitidis cells of groups A, B, C and Y were extracted with CaCl2. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of each extract showed a multibanded pattern characterized by the presence of three to four major proteins. Immunization of mice with individual extracts induced homologous bactericidal reactions. In addition, the extracts from groups B and C induced heterologous bactericidal reactions (B-C, C-B). The sera of mice immunized with a mixture of group A, B, and Y extracts showed a high bactericidal titre against the three N. meningitidis groups forming the mixture. Moreover, this bactericidal activity had a large spectrum against different strains from groups A, B, Y and also C. After immunization of mice with the individual extracts, each of the sera was shown by immunoblotting to contain antibodies reacting with some of the corresponding proteins. Mice immunized with the mixture showed a significant reduction of bacteraemia following challenge with either of N. meningitidis groups A, B or C. These results suggest that a mixture of OMP from different N. meningitidis groups may have the potential for a meningococcal polyvalent vaccine.