Preparation of ConjugateD Neisseria Meningitidis Type A Capsular Polysaccharide with Recombinant Protein of Hepatitis B as an Immunogen

Polysaccharide vaccines are effective in individuals from about the two years of age but, as they elicit T-cell independent immunity, they are not effective in younger children. In contrast, polysaccharide-protein conjugates are shown to be highly immunogenic in infants and induce T-cell dependent immunity. In this study, capsular polysaccharide of Neisseria meningitidis type A (NMA-CPS) was attached to recombinant protein of hepatitis B surface antigen (rHbsAg) covalently using amidation method. Immunization was done, choosing 2 groups of rabbits. Pure NMA-CPS and conjugated molecule were injected to groups 1 and 2, with a 15-day interval, intramuscularly. The bleeding was performed at days 0, 15, 30, 45 and titers of sera were measured via serum bactericidal assay. Polysaccharide bactericidal titer on days 15, 30 and 45 was almost identical and there was no increase in titer. But, in the first injection of the conjugate, the titer was much more (about twice of purified polysaccharide), and in the second injection, increased. Results display that conjugated molecules cause more immunity than pure capsular polysaccharide, and can stimulate cellular immunity.