CD96 is one of the immune superfamily members and it is identified as a T cell-specific receptor. In this study, we cloned a CD96 from Nile tilapia (Oreochromis niloticus, named OnCD96). The open reading frame of OnCD96was 1371 bp, encoding a protein of 456 amino acids. Sequence alignment analysis indicated that OnCD96 contained two Ig-like domains in entodomain, proline-rich motif, and ITIM motif in the cytoplasm. Subcellular localization studies showed that OnCD96 was distributed mainly in the cytoplasm and on the cytoplasmic membrane. In healthy tilapia, OnCD96 was distributed in all the tested tissues and relatively higher in the liver. After Streptococcus agalactiae infection, the expression of OnCD96 in the thymus, brain, and spleen reached its peak at 72 h, 48 h, and 24 h, respectively. After stimulation with poly I:C, the expression of OnCD96 in thymus and spleen reached its peak at 6 h and 24 h respectively. While, the expression in the brain had double peaks, which were at 24 h and 96 h. After stimulation with Keyhole limpet hemocyanin (KLH), a classical T cell-dependent antigen, the expression of OnCD96 was significantly up-regulated in blood and head kidney. Moreover, compared with the first challenge, OnCD96 was up-regulated earlier after the second challenge. Yeast two-hybrid assay indicated that there might be interaction between OnCD96 and OnNecl5. These results suggested that OnCD96 plays an important role during pathogens infection, and the interaction between CD96 and Necl5 is conserved in Nile tilapia.
