Immunogenicity and protective efficacy of Vibrio harveyi pcFlaA DNA vaccine in Epinephelus awoara

The FlaA gene from Vibrio harveyi, with a short nucleotide sequence encoding the Flag marker, was cloned into the eukaryotic expression vector pcDNA3.1(+) (designated as pcFlaA). Ninety grouper (Epinephelus awoara) were separated into three equal size groups. An experimental group was immunized with pcFlaA, Control I group was immunized with the vector pcDNA3.1(+), and Control II group was immunized with PBS. The expression of pcFlaA mRNA and protein was examined using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. We also evaluated the immunogenicity and protective efficacy of pcFlaA against V. harveyi by measuring the lymphocyte proliferation response and serum levels of specific antibody and conducting a bacterial challenge test. We successfully transfected the fish muscle with pcFlaA. The pcFlaA mRNA and protein was expressed in the muscle cells for up to one month following injection. The proliferation response of lymphocytes in fish immunized with pcFlaA was significantly higher than in control group II. Furthermore, the immunized fish generated specific antibody. The vaccination also resulted in significantly higher survival during the bacterial challenge test.