We have recently described an mAb, anti-Ti gamma A, that recognizes an antigenic determinant carried by a TCR gamma chain. This antibody binds to approximately 3% of human PBLs and delineates a CD2+, CD3+, TCR-alpha/beta-, CD4-, CD8+/-, CD5+, NKH1-, and HLA class II- subset. The present study was designed to identify the gene encoding the Ti gamma A epitope. A first analysis was carried out on a previously characterized TCR gamma + fetal-cloned cell line termed F6C7. It was found that F6C7 cells have one gamma rearrangement on each chromosome: one joins V gamma 3 to J gamma 1, and the second joins V gamma 9 to J gamma P. Because only the latter allele appeared to be transcribed in the F6C7 lymphocytes, these data strongly suggested that anti-Ti gamma A mAb is specific for either a V gamma 9 or a V gamma 9-J gamma P-encoded peptide. To confirm this point, we studied an additional series of 13 randomly selected Ti gamma A+ cloned cells derived from peripheral blood of three distinct adult individuals. Each one of these lymphocytes was shown to both possess and transcribe a V gamma 9-J gamma P-C gamma 1-rearranged gene. It is therefore concluded that a predominant subpopulation of CD3+ TCR-alpha/beta- human circulating T lymphocytes (namely, the subset defined by anti-Ti gamma A mAb) surface expresses a gamma protein with a limited potential of variability from one cell to another.

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