Full activation and function of T cells in teleost require collaboration of the first and co-stimulatory signals

T cells response in mammals requires synergism of the first signal and co-stimulatory signal. However, whether and how dual signaling regulates the T-cell response in early vertebrates remains unknown. In present study, we found that the teleost Nile tilapia Oreochromis niloticus encodes the key components of LAT signalosome: LAT, ITK, GRB2, VAV1, SLP-76, GADS, and PLC-γ1. These components are evolutionarily conserved, and CD3ε mAb-induced T-cell activation markedly increased their expression; while at least ITK, GRB2, and VAV1 could interact with LAT to form the signalosome. Downstream of the first signal, the NF-κB, MAPK/Erk, and PI3K-AKT pathways were activated upon CD3ε mAb stimulation. Furthermore, treatment of lymphocytes with CD28 mAbs triggered the AKT-mTORC1 pathway downstream of the co-stimulatory signal. A combined stimulation using CD3ε plus CD28 mAbs enhanced the phosphorylation of Erk1/2 and S6 and elevated the expression of NFAT1, c-Fos, IL-2, CD122, and CD44, signifying T-cell activation. Moreover, instead of the first signal or co-stimulatory signal alone, both dual signals are required for T-cell proliferation. In addition, full T-cell activation was accompanied by marked apoptosis and cytotoxic response. Therefore, our findings suggest that tilapia relies on dual signaling to maintain the optimal T-cell response, providing a novel perspective for understanding the evolution of the adaptive immune system.