Kinetics of T lymphocyte subsets and B lymphocytes in response to immunostimulants in flounder (Paralichthys olivaceus): implications for CD4(+) T lymphocyte differentiation

CD4(+) T lymphocytes play crucial roles in the adaptive immune system. CD4, as the most effective marker to delineate the T-helper subsets, was identified in many fish species. Two CD4 homologs, CD4-1 and CD4-2, have been reported in flounder (Paralichthys olivaceus). In this study, monoclonal antibodies (mAbs) against CD4-1 and CD4-2 of flounder were produced, CD4(+) T lymphocytes were isolated and identified, and the variations in CD4(+) and CD8(+) T lymphocytes and IgM(+) B lymphocytes after Poly I:C, PMA or β-glucan stimulation were investigated. Then, the expression of transcription factors and cytokines in sorted CD4(+) T lymphocytes was analyzed. The results showed that the mAbs were specific to flounder CD4-1(+) and CD4-2(+) T cells. CD4-1(+) and CD4-2(+) cells responded to all three stimulants, while CD8(+) T lymphocytes only give a strong response to Poly I:C, and the percentages of IgM(+) B lymphocytes showed a tendency to increase. After stimulation, the expression of transcription factors and cytokines of Th1, Th2 and Th17 cells varied in CD4(+) T cells. These results will provide crucial foundations for the differentiation and function of teleost CD4(+) T lymphocytes.