CD3 γ/δ in sea bass (Dicentrarchus labrax): molecular characterization and expression analysis

Abstract

The CD3 complex is the common marker on the surface of both ab and gd T cells and is essential for formation of the T-cell receptor complex and for T-cell activation. In this paper, we report the gene cloning and molecular characterization of a CD3g/d homologue in sea bass (Dicentrarchus labrax), the analysis of transcription levels in lymphoid and non-lymphoid organs and the gene regulation after in vitro stimulation with LPS and PHA. Four cysteine residues in the extracellular domain, involved in the constitution of immunoglobulinlike domain, are present in sea bass CD3g/d sequence and they are conserved both in number and position from mammals to teleost sequences. Similar to other known CD3g/ds, in sea bass CD3g/d there is also a conserved immunoreceptor tyrosine-based activation ITAM motif that could be responsible for its individual signal transduction capacity. The real time RT-PCR basal analysis shows the highest level of CD3g/d mRNA in thymus, followed by peripheral blood leucocytes, spleen, gills, gut, liver, head kidney, brain and muscle. The expression analysis under stimuli condition reveals a significant decrease of CD3g/d expression after LPS stimulation and a significant increase after PHA-L stimulation, in agreement with mammals results. In conclusion, these data allow us to affirm that sea bass CD3g/d can be used as a T cell marker and will help in adding new insight on the immune response mechanisms of sea bass.