学位論文の一部を構成しているため、に本文を掲載。 A signal joint (sj) T-cell receptor excision circle (TREC) is produced by T-cell receptor (TCR)gene rearrangements during αβ T-cell maturation in the thymus. sjTREC have been studied as a marker of thymic function in several spices. We designed specific primers for δrec-ψJα sj region to identify the location of the bovine sjTREC region and determined the nucleotide sequence of the PCR product. The obtained sequences were subjected to a BLAST search, which identified a matching region. This matching region contained TCR δ genes and was identified on bovine chromosome 10. We also confirmed the polymorphism of the sj region by sequencing of 10 PCR products, and observed irregular insertion of bases in the δrec-ψJα recombination signal sequence. We then developed a quantitative PCR (QPCR) assay for evaluation of sjTRECs level in order to evaluate bovine thymic function for application in the veterinary clinic. This QPCR assay specifically amplified the sj region of bovine sjTREC and could detected 101–107 copy numbers of sjTRECs. Using this assay we found that the number of sjTRECs in peripheral blood mononuclear cells was less than 10% that of the thymus.