Anti-Id Ab2-6F9 mimics capsular PS of N. merzingitidis group C (MCPS). Anti-Id Ab2-6F9 stimulates an anti-MCPS antibody response in mice that is specific, protective and T cell-dependent. The immunogenic "internal image of antigen" protein sequence of anti-Id Ab2-6F9 was determined from the DNA sequence of the unique VH CDR3 region and computer modeling. This data was used to prepare a synthetic peptide mimic (P3) of MCPS.