Journal
GENES
Volume 12, Issue 4, Pages -Publisher
MDPI
DOI: 10.3390/genes12040544
Keywords
γ δ T cell; T cell receptor; TRA; TRD locus; variable; diversity; joining and constant genes; complementarity determining region-3; δ chain; somatic hypermutation; Camelidae
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Funding
- University of Bari
- University of Salento
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The research found that compared to other animals, the number of variable genes in camel γδ T cells is lower, but it is still able to be expanded and diversified through somatic hypermutation mechanisms. In addition, the multiple insertions of D genes contribute to the increased diversity of camel δ chain antigen binding sites.
The role of gamma delta T cells in vertebrate immunity is still an unsolved puzzle. Species such as humans and mice display a low percentage of these T lymphocytes (i.e., gamma delta low species) with a restricted diversity of gamma delta T cell receptors (TR). Conversely, artiodactyl species (i.e., gamma delta high species) account for a high proportion of gamma delta T cells with large gamma and delta chain repertoires. The genomic organisation of the TR gamma (TRG) and delta (TRD) loci has been determined in sheep and cattle, noting that a wide number of germline genes that encode for gamma and delta chains characterise their genomes. Taking advantage of the current improved version of the genome assembly, we have investigated the genomic structure and gene content of the dromedary TRD locus, which, as in the other mammalian species, is nested within the TR alpha (TRA) genes. The most remarkable finding was the identification of a very limited number of variable germline genes (TRDV) compared to sheep and cattle, which supports our previous expression analyses for which the somatic hypermutation mechanism is able to enlarge and diversify the primary repertoire of dromedary delta chains. Furthermore, the comparison between genomic and expressed sequences reveals that D genes, up to four incorporated in a transcript, greatly contribute to the increased diversity of the dromedary delta chain antigen binding-site.
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