Abstract

CD3 is an essential component of the TCR-CD3 complex which plays a key role in adaptive immunity . Non-mammalian CD3 complex consists of CD3γ/δ, CD3ε and CD3ζ subunits. In this study, homologues of CD3γ/δ and CD3ε (termed Ci CD3γ/δ and Ci CD3ε) have been identified in grass carp ( Ctenopharyngodon idella ). Like their counterparts from other vertebrates, the Ci CD3γ/δ and Ci CD3ε are clustered in the same locus in the genome and encode proteins which are structurally conserved, comprising a signal peptide , an extracellular domain, a transmembrane domain and a cytoplasmic tail containing two ITAM motifs. Sequence analyses identified two novel conserved motifs in the cytoplasmic tail of Ci CD3γ/δ and Ci CD3ε, one is composed of an arginine and lysine motif (RK or RR) at the C terminus of Ci CD3γ/δ and a proline rich domain (PxxPxP/Q) located at the N terminus of ITAM motifs of Ci CD3ε. Both genes were highly expressed at the mRNA level in the spleen and gills of healthy fish and could be modulated by infection of Flavobacterium columnare and grass carp reovirus . A monoclonal antibody against the Ci CD3γ/δ (GC38T) was produced and showed good reactivity with the native molecule in Western blotting analysis and flow cytometry. The Ci CD3γ/δ + cells were analysed in the primary leucocytes, accounting for 5.5% of lymphocytes isolated from spleen, 4.5% from head kidney and 2.8% from peripheral blood. The Ci CD3γ/δ + cells were localized in the gills and head kidney by fluorescent confocal microscopy .