Extensive involvement of CD40 and CD154 costimulators in multiple T cell-mediated responses in a perciform fish Larimichthys crocea.

CD40 and CD154 are well-characterized costimulatory molecules involved in adaptive humoral immunity in humans and other mammals. These two costimulatory molecules were found to be originated from teleost fish during vertebrate evolution. However, the functionality of fish CD40 and CD154 remains to be explored. In this study, we identified the CD40 and CD154 homologs (Lc CD40 and Lc CD154) from large yellow croaker (Larimichthys crocea), a marine species of the perciform fish family. The Lc CD40 and Lc CD154 share conserved structural features to their mammalian counterparts, and are widely expressed in immune-relevant tissues and leukocytes at different transcriptional levels. Immunofluorescence staining and FCM analysis showed that Lc CD40 and Lc CD154 proteins are distributed on MHC-II+ APCs and CD4-2+ T cells, and are significantly upregulated in response to antigen stimulation. Co-IP assay exhibited strong association between Lc CD40 and Lc CD154 proteins. Blockade of Lc CD154 with anti- Lc CD154 antibody (Ab) or recombinant soluble Lc CD40-Ig fusion protein remarkably decreased the MHC-II+ APC-initiated CD4+ T cell response upon Aeromonas hydrophila stimulation, and alloreactive T cell activation as examined by mixed lymphocyte reaction (MLR). These findings highlight the costimulatory role of Lc CD40 and Lc CD154 in T cell activities in Larimichthys crocea. Thus, the CD40 and CD154 costimulators may extensively participate in the regulation of multiple T cell-mediated immune responses in teleost fish. It is anticipated that this study would provide a cross-species understanding of the evolutionary history of CD40 and CD154 costimulatory signals from fish to mammals. • Identification of CD40/CD154 in perciform fish provides further evidence for the origin of these two costimulators in fish. • CD40/CD154 regulate APC-initiated CD4+ T cell activation in fish. • CD40/CD154 are involved in regulating allogeneic T cell reaction in fish. [ABSTRACT FROM AUTHOR]