CD40 plays roles in T cell-dependent response and B cell activation and differentiation in Nile tilapia (Oreochromis niloticus)

CD40 is a member of the TNF receptor family and plays critical roles in T cell-dependent (TD) immune response in mammals. However, limited information on CD40 functional characterization is known in teleost fish. In this study, Nile tilapia (Oreochromis niloticus) CD40-like (OnCD40) was cloned and characterized with its expression patterns in TD immune response, including the process of B cell activation and differentiation. The OnCD40 has a 948 bp length open reading frame and was expressed wildly in immune tissues, especially in peripheral blood. In addition, the OnCD40 expression level was much higher in IgMhi naive/activated B cells than that of IgMlo plasma-like B cells. Further, the expression of OnCD40 was significantly up-regulated after in vivo challenge of keyhole limpet hemocyanin (KLH), and the increased level of OnCD40 expression was evidently higher in the second stimulation than the first one. The significant up-regulation of OnCD40 transcript also appeared following KLH immunization in vitro. Moreover, by in vitro stimulation of recombinant Oreochromis niloticus interleukin 6 ((r)OnIL-6), recombinant Oreochromis niloticus interleukin 10 ((r)OnIL-10), or induction of anti-OnIgM monoclonal antibody (mAb), the OnCD40 expression was markedly up-regulated following the B cell activation or differentiation. Taken together, the findings in this study suggest that OnCD40 might be involved in TD humoral immune response and plays roles in B cell activation and differentiation in Nile tilapia.