Type-specific antigens of Neisseria meningitidis serogroup A

By using Ouchterlony immunodiffusion techniques, we defined three unique antigenic determinants (A1, A2, and A3) among six isolates of Neisseria meningitidis serogroup A. Two of these determinants (A2 and A3) were identified as lipopolysaccharides in nature and were not found to occur on the serogroup B strains of N. meningitidis that we examined. The A1 determinant commonly occurred among the serogroup B strains and was identified as a protein determinant.