EACH OF THE 2 PRODUCTIVE T-CELL RECEPTOR ALPHA-GENE REARRANGEMENTS FOUND IN BOTH THE A10 AND BM 3.3 T-CELL CLONES GIVE RISE TO AN ALPHA-CHAIN WHICH CAN CONTRIBUTE TO THE CONSTITUTION OF A SURFACE-EXPRESSED ALPHA-BETA-DIMER

The H-2 K(b) specific cytotoxic T cell clone BM3.3 carries two productive TCR alpha gene rearrangements but expresses a single detectable TCR alpha-beta chain combination on its surface. However, when separately analyzed by gene transfer, both productive alpha gene rearrangements are translated into alpha-chains capable of pairing with the BM3.3 beta-chain and of cell surface expression. Similar observations have been made with the products of the two productive alpha-gene rearrangements previously identified in the A10 T cell clone. These observations contrast with those made for the two TCR alpha-chains expressed in the MS202 T clone. In the latter instance, when analyzed by gene transfer, one of the alpha-chains was unable to make a pair with the beta-chain. Consequently, when considered with respect to the mechanisms of TCR allelic exclusion, our data suggest that the mere expression of a TCR alpha-beta-dimer on the surface of immature CD4+CD8+ thymocytes may be necessary but not sufficient to shutdown further alpha-gene rearrangements. Rather, the ability of a TCR alpha-beta dimer to be positively selected may be needed to trigger the maturation of thymocytes to a stage devoid of recombinase activity. Alternatively, if non-dividing CD4+CD8+CD3+ small thymocytes do not experience secondary alpha-gene rearrangement, our data suggest that TCR alpha gene rearrangements are attempted quasi-simultaneously on both alpha-alleles.