Abstract：The cluster of differentiation 3 (CD3) molecules are expressed on the surface of T-cell and involved in T-cell activation by binding to T cell receptor complex non-covalently. In this paper, three CD3 subtypes (CD3γ/δ, CD3ε and CD3ζ) cDNA were obtained from Lateolabrax japonicus by RT-PCR and rapid amplification of cDNA ends (RACE). The full length cDNA sequence of CD3γ/δ was 1 231 bp in length, containing a 5'-UTR of 99 bp, 3'-UTR of 583 bp and ORF of 549 bp which encoded a putative protein of 182 amino acids. The CD3ε cDNA was 2 145 bp in length with 186 bp 5'-UTR, 1 434 bp 3'-UTR and 525 bp ORF coding a protein of 174 amino acids. The full length cDNA sequence of CD3ζ was 1 231 bp in length, including a 5'-UTR of 56 bp, 3'-UTR of 772 bp and ORF of 453 bp which encoded a deduced protein of 150 amino acids. The CD3γ/δ and CD3ε in Lateolabrax japonicus were similar in structure with an Ig-like extracellular domain, a transmembrane peptide and a cytoplasmic tail with one immunoreceptor tyrosine-based activation motif (ITAM). There were 4 cysteins in the extracellular domains of CD3γ/δ and CD3ε, the first 2 cysteins involved in Ig-fold stabilisation and the last two in CxxCxE motif important for dimerization. However, The CD3ζ molecule had a different structure with a short extracellular part of 5 amino acids, a transmembrane region and a long cytoplasmic tail with three ITAM motifs. Analysis of DNA and cDNA sequences showed that the ORF part of CD3γ/δ gene contained 6 exons and 5 introns while CD3ε gene contained 7 exons and 6 introns. qRT-PCR results showed that CD3γ/δ, CD3ε and CD3ζ were expressed in all tissues tested with higher levels in gill, spleen, headkidney and intestine and lower levels in fat, liver, eye and brain. The expression of CD3γ/δ, CD3ε and CD3ζ increased obviously in headkidney, intestine and spleen after intraperitoneal injection of Vibrio harveyi. The results indicated that CD3s were involved in immune response of T cells after bacterial infection. This obtained information will provide a theoretical basis for studying the molecular mechanism of fish CD3 in regulating fish immune response to pathogens.
