Studies on Phage Displayed Mimotopes of a Protective Monoclonal Antibody (SSj14) Against Schistosoma japonicum

To obtain peptides mimicking epitopes of a protective McAb SSj14 specific to Schistosoma japonicum and investigate their immunoprotective effects. A random 12 phage peptide library was screened using purified McAb SSj14; 33 clones were picked up for specificity identification by ELISA. The epitope of each positive clone was detected by the sequencing analysis technique. The antigenicity of three positive clones (P1, P2, and P11) and their mixture cocktail were further confirmed by western blotting, and their protective efficiency was evaluated by a mice vaccination experiment. IL-12 level between the vaccinated mice and controlled mice were compared. 30 positive phage clones were obtained, which represented 11 different epitopes, respectively, and there was a similar sequence 'H-N/Q-X-S-P/F-X-L-A-T' among all of the epitopes. Western blotting showed that all of the three tested clones were recognized by McAb SSj14. Significant adult worm reduction (13.84 % - 52.83 %), liver tissue egg reduction (34.17 % - 65.47 %) as well as fecal egg reduction (28.89 % - 73.78 %) were observed in mice vaccinated with phages of P1, P2, and P11 and a mixture of three clones. When compared with those of the blank control group, the mice vaccinated with the mixture of phage clones received higher protection than any of the mice injected with only one kind of clone phages. At the same time, the IL-12 level in the serum of vaccinated mice was found to be higher than those of the blank control group, thus suggesting that IL-12 may correlate with the protective efficiency induced by the clone phages. The study provides a new method of developing an effective vaccine against S. japonicum.