Usage of human T-cell receptor V beta, J beta, C beta, and V alpha gene segments is not proportional to gene number.

Certain T-cell receptor (TCR) beta-chain variable (V), joining (J), and constant (C) gene segments, as well as TCR alpha-chain V gene segments, are disproportionally represented in TCR alpha and beta cDNA libraries derived from PHA-stimulated peripheral blood lymphocytes. Sequences of 138 TCR alpha clones and 96 TCR beta clones were determined and of these 128 TCR alpha clones and 88 TCR beta clones were found to contain unique combinations of V, J, and C gene segments or to display diversity in N region nucleotides. The frequency of the V, J, and C genes used in the assembly of unique transcripts was ascertained. Of the 24 reported V beta gene families, 21 were observed among the 88 TCR beta clones including four V beta families (V beta 1, V beta 2, V beta 3, and V beta 4) that were represented in the sample 2 1/2-5 times more frequently than would be expected on the basis of copy number within the gene complex. Seventy-eight percent of the clones were positive for C beta 2 and more than half of the clones (53%) used one of two J beta 2 genes: J beta 2.1 was present in 27 clones and J beta 2.7 in 20 clones. TCR V alpha families were also disproportionately represented in this sample. Twenty-five of 30 V alpha families were observed in the sample of 128 clones including six recently reported V alpha families. Three V alpha families, V alpha 2, V alpha 8, and V alpha 23, accounted for approximately 40% of the TCR alpha clones and were represented at 18%, 9.4%, and 13.3%, respectively. Both V alpha 2 and V alpha 8 gene families contain more than one gene; thus the number of clones observed in these families may, in part, be related to gene number. However, V alpha 23, which appears to be a single-copy gene family, is significantly overrepresented in this sample. Although disproportional usage of V beta genes may be accounted for by superantigen exposure, reasons for disproportional usage of J beta, C beta, and V alpha genes are presently unknown.