Recombinant maltose-inducible porin LamB of Aeromonas hydrophila induces TH2-biased mixed immune response and generates cross-species agglutinating antibodies in the murine model.

BACKGROUND: Aeromonas hydrophila is a major freshwater fish pathogen responsible for significant economic losses to the aquaculture industry. Its virulence factors include proteins involved in primary adhesion, pili, flagella, O-antigen, outer membrane proteins, and adhesins, etc. Among these, the outer membrane maltose-inducible porin functions as an adhesin and can be a potential vaccine candidate.

METHODS AND RESULTS: In the present study, the maltose-inducible porin (LamB) of A. hydrophila was heterologously overexpressed, purified and assessed for its immunogenic potential in a murine model. The gene encoding mature LamB was cloned into pRSET-A expression vector. Recombinant LamB (rLamB) carrying a 6×-histidine tag was expressed as inclusion bodies in E. coli BL21(λDE3), purified from solubilized inclusion bodies by metal affinity chromatography to near homogeneity, and refolded. Immunization of mice with rLamB generated high-titer anti-rLamB antibodies with high specificity. The anti-rLamB antisera agglutinated live A. hydrophila cells in vitro and recognized other Aeromonas species, suggesting its possible application in the diagnosis of Aeromonas infection and potential as a candidate for broad-spectrum vaccine development. Antibody isotyping and cytokine ELISA indicated a TH2-biased mixed immune response.

CONCLUSION: Recombinant LamB of Aeromonas hydrophila elicited strong and specific immune responses, generating high-titer antibodies that agglutinated live bacteria and cross-reacted with other Aeromonas species. These findings collectively suggest that rLamB of A. hydrophila may have potential as a vaccine candidate for broad-spectrum vaccine development and possible diagnostic applications against heterogeneous A. hydrophila.