ZAP70 activation is an early event of T cell immunity that involved in the anti-bacterial adaptive immune response of Nile tilapia

ZAP70 is essential for initiating the early events of T-cell antigen receptor (TCR) signaling cascade to ensure proper T cell activation and function. However, whether this molecule takes part in the T cell immune response of early vertebrates remains unclear. In the present study, using a teleost model Nile tilapia (Oreochromis niloticus), we investigated the potential involvement of ZAP70 in the T cell activation and adaptive immunity of fish species. Both primary and tertiary structures of O. niloticus ZAP70 (On-ZAP70) are highly conserved with those from other vertebrates. On-ZAP70 protein was widely expressed in lymphoid tissues, and with the highest level in thymus. Once Nile tilapia was infected by Aeromonas hydrophila, mRNA of On-ZAP70 in spleen lymphocytes was induced on day 5 and 8 after infection; meanwhile, phosphorylation of On-ZAP70 was also enhanced, suggesting that On-ZAP70 potentially participated in primary adaptive immune response of Nile tilapia. Furthermore, the frequency of ZAP70 positive lymphocytes was increased during the anti-bacterial adaptive immune response. More importantly, when spleen lymphocytes were activated by T cell specific mitogen PHA, a dramatical augment of On-ZAP70 could be observed at transcription, phosphorylation and cellular level, indicating the involvement of this molecule in T cells activation of Nile tilapia. Altogether, our results demonstrated that ZAP70 activation is an early event of T cell immunity that involved in the anti-bacterial adaptive immune response of Nile tilapia, and thus provided a new evidence to understand the evolution of the lymphocyte-mediated adaptive immunity.