Interleukin-2 inducible T cell kinase (ITK) may participate in the anti-bacterial immune response of Nile tilapia via regulating T-cell activation

Interleukin-2 inducible T cell kinase (ITK) plays a predominant role in the T-cell receptor (TCR) signaling cascade to ensure valid T-cell activation and function. Nevertheless, whether it regulates T-cell response of early vertebrates remains unknown. Herein, we investigated the involvement of ITK in the lymphocyte-mediated adaptive immune response, and its regulation to T-cell activation in the Nile tilapia Oreochromis niloticus. Both sequence and structure of O. niloticus ITK (OnITK) were remarkably conserved with its homologues from other vertebrates, implying its potential conserved function. OnITK mRNA was extensively expressed in lymphoid-related tissues, and with the relative highest level in peripheral blood. Once Nile tilapia was infected by Edwardsiella piscicida, OnITK in splenic lymphocytes was significantly up-regulated on 7-day post infection at both transcription and translation levels, suggesting that OnITK might involve in the primary adaptive immune response of teleost. Furthermore, upon splenic lymphocytes were stimulated by T-cell specific mitogen PHA, OnITK mRNA and protein levels were dramatically elevated. More importantly, treatment of splenic lymphocytes with specific inhibitor significantly crippled OnITK expression, which in turn impaired the inducible expression of T-cell activation markers IFN-γ, IL-2 and CD122, indicating the critical roles of ITK in regulating T-cell activation of Nile tilapia. Taken together, our results suggest that ITK takes part in the lymphocyte-mediated adaptive immunity of tilapia, and is indispensable for T-cell activation of teleost. Our findings thus provide novel evidences for understanding the mechanism regulating T-cell immunity of early vertebrates, as well as the evolution of adaptive immune system.