Immune response characterization and vaccine potential of a recombinant chimera comprising B-cell epitope of Aeromonas hydrophila outer membrane protein C and LTB

Aeromonas hydrophila is one of the most virulent fish pathogens, causing colossal economic losses to the aquaculture industry annually. The absence of a safe and effective vaccine makes it very difficult to control this infection. Outer membrane proteins have been widely illustrated to confer protective immunity against a broad spectrum of gram negative bacteria. In the current study, we have analyzed the ability of B-cell epitopes of A. hydrophila's outer membrane protein C (OmpC) to confer protection against bacterial virulence. Bioinformatic algorithms were used to predict linear B-cell epitopes of OmpC and the corresponding nucleotide sequences were cloned in translational fusion with heat labile enterotoxin B subunit (LTB) of E. coli. Of the three recombinant LTB.epitope fusion proteins evaluated, antisera against the fusion protein comprising the epitope stretch of 143-175 amino acids gave maximum cross reactivity with the parent protein OmpC. The anti-fusion protein antisera contained both OmpC- and LTB-specific antibodies. The fusion proteins' LTB moiety retained its ability to bind to the GM1 ganglioside receptor, an essential requirement for its adjuvanicity. Antibody isotyping, cytokine ELISA, and cytokine array analysis revealed a Th2 skewed type immune response along with the presence of some relevant Th17 and Th1 cytokines involved in conferring protective immunity. Surface exposure of the epitope143-175 on live A. hydrophila membrane was investigated and validated using bacterial agglutination and flow cytometry analysis using anti-fusion protein antisera. Our results strongly support the potential of B-cell epitope143-175 of OmpC of A. hydrophila, in fusion with the LTB, as an effective and promising vaccine candidate against this bacterium.