Genomic sequencing of the bovine T cell receptor loci and analysis of T cell populations in the peripheral blood of ruminant and non-ruminant species

T cells are important effectors of the immune system that act to regulate the immune response and participate in the destruction of foreign cells. Of the two major populations of T lymphocytes, the alphabeta population is well studied whereas gammadelta cells display a number of idiosyncratic properties. gammadelta T lymphocytes are the first to appear in ontogeny [1], have the ability to present antigen [2] and are able to recognize pathogen associated molecular patterns [3], stress molecules [4] and phosphoantigens [5]. gammadelta T cells preferentially localize to epithelial sites and are expressed in high percentages in the peripheral blood of certain species such as chickens and cattle [6, 7].;Expression analysis of the bovine TCR loci indicates that although alpha, beta and gamma all display preferential gene segment usage, the TCR gamma locus utilized preferential expression considerably more than either TCR alpha or beta. A particular TCRGC region that is highly utilized (C6) contains four copies of a TTEPP ruminant specific repeat and it is postulated that the function of this repeat, which is not presently known, may relate to high peripheral blood gammadelta T cell expression.;A second study was performed to correlate high peripheral blood gammadelta T cell expression with digestive system type. A flow cytometry study performed with 42 different species of animals identified anti-TCR alphabeta, gammadelta, CD3 and WC1 antibodies that were cross-reactive with 30 different species including mammals and reptiles. Using cross-reactive antibodies from this experiment, 15 species were immunophenotyped to calculate peripheral blood gammadelta T cell populations. The results of the immunophenotyping experiment revealed that high expression of peripheral blood gammadelta T cells cannot be correlated with digestive system type, as evidenced by the information that ruminant and non-ruminant primates contain the same percentages of gammadelta T lymphocytes.;As there is no correlation with digestive system type, it is hypothesized that high gammadelta T cell percentages may be connected with placenta use. Animals with epitheliochorial placentae are unable to transfer antibodies from mother to fetus; therefore, the neonate is born with no passive immunity [8]. It is postulated that since gammadelta T cells are expressed highly in young animals that these cells may act as the early immune system in the neonate. It is recommended that future studies investigating placentation and gammadelta T cells begin with an analysis of gammadelta T cell percentages in epitheliochorial primates of the infraorder Strepsirhini (lemurs and lorises) as these species are born without passive immunity.;To investigate if high expression of gammadelta T cells in cattle is due to an alteration in the alphabeta or gammadelta TCR gene structure, 0.7 megabases of bovine genomic DNA sequence was acquired that encompasses the J and C regions of the TCR alpha and beta loci as well as the entire gamma locus. Annotation and analysis of these loci revealed that both the TCR alpha and beta loci contain well conserved joining (J) gene segments, recombination signal sequences (RSS) and constant (C) regions. This study identified a novel constant region (C3) in the TCR beta locus. It was also verified that the bovine TCR gamma locus exists in two separate sections on the chromosome. The TCRgamma gene locus has weak conservation of canonical J gene segments.