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CD3ε is involved in host immune response against challenges in Nile tilapia (
 Orechromis niloticus
 )

CD3 is an important membrane molecule of mature T cells. TCR‐CD3 complex plays important roles in the activation and signal transduction of T cells. In this study, the CD3e (OnCD3e) gene was cloned from Nile tilapia (Oreochromis niloticus), and its tissue distribution was detected by qPCR. The expression changes in CD3e were analysed after three challenges (S. agalactiae, A. hydrophila and poly (I:C)) in vivo and in vitro. The open reading frame (ORF) of OnCD3e contains 531 bp, encoding 176 amino acids, which found that OnCD3e consists of conserved amino acid residues and motifs (cysteine residues, CXXC motif, immunoreceptor tyrosine‐based activation motifs and PxPDY). In addition, tissue distribution displayed that OnCD3e has the highest expression in thymus and significant expression level in mucosal immune‐related tissues (intestine and gills). In vivo, all three challenges could significantly up‐regulate the expression of CD3e in the head kidney and spleen. For further in vitro assays, after poly (I:C) stimulation, OnCD3e appeared significant up‐regulation at 3 hr post stimulation, and two pathogenic bacteria also induce significant up‐regulation of OnCD3e in spleen leucocytes (12 hr). These results suggested that OnCD3e was likely to get involved in host immune response against pathogenic challenges.