Induction of protective immunity against S. typhi infection with by peptide mimics of LPS epitopes

Objective To characterize three peptide mimics of lipopolysaccharide (LPS) epitopes which induce the humoral immune response to LPS and the protective immunity against S. typhi bacterium. Methods The three peptide mimics of LPS epitopes were synthesized according to sequences of phage clones screened from phage display peptide library using anti-LPS antibody as target. Peptide mimics was conjugated to Blue Carrier (BC) as vaccine. Balb/c mice were immunized with the peptide-BC, and then challenged with Gram-negative bacteria. Anti-LPS antibodies in peptide-BC-immunized mice were detected by ELISA using peptide-BSA as coating antigen. Survival days of mice were observed. Results Specific antibodies against S. typhi-LPS 7261 and E.coli-LPS 2630 were elicited in mice immunized with peptide 13a-, peptide 13b-, and 12w-BC conjugations, and could be boosted by inactive or live bacteria. After challenge with S. typhi, the survival time of mice immunized with peptide 13a-, peptide 13b- and 12w-BC conjugations were (6.5 ± 0.77), (9.5 ± 1.38), and (9.3 ± 0.75) days, respectively. While the survival time of mice immunized with BC was 5 days. Conclusion These results suggest that these three peptides can mimic the antigenicity of LPS epitopes and can induce secondary antibody response, like thymus-dependent antigens. These peptide mimics could be a new vaccine candidate of LPS.