Immune response and protective effect against Vibrio anguillarum induced by DNA vaccine encoding Hsp33 protein

Heat shock proteins (HSPs) are considered as potent vaccine candidates against a wide range of bacterial diseases. In the present study, a recombinant DNA plasmid based on the expression of Hsp33 gene was constructed and intramuscularly administrated to flounder to elucidate whether it induces immune response and prevents the infection of Vibrio anguillarum in flounder model. Meanwhile, the expression of pHsp33 was analyzed in vitro and in vivo. The results revealed that pHsp33 was successfully expressed both in transfected hirame natural embryo cell lines and injected flounder muscle, suggesting the functionality of pHsp33 to express Hsp33 protein. Fish, when intramuscularly injected with pHsp33 vaccine, exhibited the production of specific antibodies, upregulation of immune related genes expression in the head kidney and increase of sIgM⁺, CD4-1⁺ and CD4-2⁺ lymphocytes in peripheral blood, spleen and head kidney, which indicated the activation of humoral and cellular immune responses. Moreover, pHsp33 upregulated the expression of immune related genes at the inoculation site, indicating the activation of local immune response. In addition, pHsp33 vaccinated flounder provided a relative percent survival of 42.86% and inhibited the pathological lesion in liver following V. anguillarum challenge. In general, the results revealed that pHsp33 could elicit local and system immune responses and confer protection for flounder, suggesting pHsp33 could serve as a DNA vaccine candidate for the control of V. anguillarum infection.