Abstract
Background : gδT cells differ fromabT cells with regard to the types of antigen with which their T cell receptorsinteract;gδT cell antigens are not necessarily peptides nor are they presented on MHC. Cattle are considered a“gδT cell high”species indicating they have an increased proportion ofgδT cells in circulation relative to that in“gδT cell low”species such as humans and mice. Prior to the onset of the studies described here, there was limitedinformation regarding the genes that code for the T cell receptor delta chains of thisgδT cell high species.Results : By annotating the bovine (Bos taurus) genome Btau_3.1 assembly the presence of 56 distinct T cellreceptor delta (TRD) variable (V) genes were found, 52 of which belong to the TRDV1 subgroup and were co-mingled with the T cell receptor alpha variable (TRAV) genes. In addition, two genes belonging to the TRDV2subgroup and single TRDV3 and TRDV4 genes were found. We confirmed the presence of five diversity (D) genes, three junctional (J) genes and a single constant (C) gene and describe the organization of the TRD locus. TheTRDV4 gene is found downstream of the C gene and in an inverted orientation of transcription, consistent with itsorthologs in humans and mice. cDNA evidence was assessed to validate expression of the variable genes andshowed that one to five D genes could be incorporated into a single transcript. Finally, we grouped the bovineand ovine TRDV1 genes into sets based on their relatedness.Conclusions : The bovine genome contains a large and diverse repertoire of TRD genes when compared to thegenomes of“gδT cell low”species. This suggests that in cattlegδT cells play a more important role in immunefunction since they would be predicted to bind a greater variety of antigens.