Developmentally regulated expression of T cell receptor β chain variable domains in immature thymocytes

A minor subset of immature (CD4-,8-) thymocytes that lack expression of the B2A2 antigen was found to express low levels of surface TCR protein as detected by mAbs F23.1 and KJ16 (reacting with protein products of the V beta 8 gene family). Interestingly, F23.1/KJ16 determinants were expressed on a two- to three-fold higher proportion of B2A2- thymocytes than mature lymph node T cells in four independent haplotypes. When expanded in short-term culture with PMA and calcium ionophore, B2A2- thymocytes retained their overexpression of F23.1/KJ16 determinants and showed a fivefold elevated level (relative to lymph node) of V beta 8-specific mRNA. Taken together, these findings suggest that expression of TCR V beta genes, like Ig genes, is developmentally regulated.