T and B lymphocytes immune responses in flounder (Paralichthys olivaceus) induced by two forms of outer membrane protein K from Vibrio anguillarum: Subunit vaccine and DNA vaccine

Abstract

To further elucidate the roles of T and B lymphocytes in fish subunit and DNA candidate vaccines for immunisation, the immune responses of T and B lymphocytes to recombinant protein (rOmpK) and plasmid OmpK (pOmpK) from Vibrio anguillarum plus cyclosporine A (CsA) were investigated in flounder (Paralichthys olivaceus). The results showed that in the rOmpK-immunised groups, the percentages of CD4-1+ and CD4-2+ T (PCD4-1+ and PCD4-2+ T) lymphocytes significantly increased to a peak on days 5 or 7. The percentages of IgM+ B (PIgM+ B) lymphocytes and specific antibodies markedly increased to a peak at weeks 4 or 5. The nine immune-related genes were significantly up-regulated and the expression levels of CD4-1, CD4-2 and MHC II genes were higher than that of CD8α, CD8β and MHC I genes. The CD4+ T lymphocytes, IgM+ B lymphocytes, and specific antibodies were significantly inhibited by CsA. Therefore, the responses of CD4+ T lymphocytes influenced the responses of the B lymphocytes and antibodies. In the pOmpK-immunised groups, the PCD4-1+, PCD4-2+, and PCD8β+ T lymphocytes significantly increased to a peak on days 11 or 14, days 9 or 11, and days 7 or 9, respectively. The PIgM+ B lymphocytes and specific antibodies significantly increased to a peak at weeks 5 or 6. Immune related genes upregulated, and CD4+ and CD8+ T lymphocytes, IgM+ B lymphocytes and specific antibodies all suppressed by CsA, suggesting that the responses of T lymphocytes subpopulations influenced B lymphocytes and antibodies responses. Therefore, the subpopulations of T lymphocytes played an important role in the immune responses induced by subunit and DNA candidate vaccines of OmpK and regulated the immune responses of B lymphocytes in flounder.