Design of T cell epitope rich OmpC peptide and its conjugation with Vi-polysaccharide: a candidate vaccine for typhoid fever (106.26)

Abstract

Abstract Here, we conjugated Vi polysaccharide with outer membrane protein C (OmpC) peptide-39 amino acid residues of S.Typhi and its immunogenicity was evaluated in mice. T cell epitopes in the OmpC were predicted using program T sites. Predominantly two regions with high content of T-cell epitopes, loop # 3a & 7 were chosen and synthesized commercially. Carbodiimide-mediated conjugation of Vi polysaccharide with synthetic OmpC peptide was achieved using ADH as a linker molecule. In various batches; obtained polysaccharide/peptide ratio was between 0.43-0.65. Total and IgG antibodies against Vi polysaccharide and OmpC peptide were measured by ELISA. No Vi antibody was detected in OmpCp and saline control group. Vi polysaccharide alone elicited very low levels of Vi antibody without any booster effect while Vi-OmpCp conjugate evoked 20 fold more efficient immune response than Vi polysaccharide. The Vi-OmpCp conjugate elicited strong booster response which persisted for longer duration. Further, adequate level of IgG antibodies were induced only by the Vi-OmpCp conjugate suggesting that T-helper cells had been induced. Although no immune response was generated against OmpCp. Therefore, selected OmpC short peptide used as carrier with Vi is assumed to be a promising candidate vaccine against typhoid fever.