T-CELL RECEPTOR-BETA CHAIN GENE REARRANGEMENT AND SELECTION DURING THYMOCYTE DEVELOPMENT IN ADULT MICE

The identification is made in normal mice of the stages in T cell development at which the rearranged beta chain of the T cell receptor (TCR) is utilized to promote T cell maturation, independent of the TCR alpha chain. In addition, evidence is provided that utilization of beta chains in T cell progenitors does not preclude differentiation to TCR gamma delta(+) T cells. This is consistent with the view that an initial consequence of beta chain expression by early thymocytes is clonal expansion, increasing the size of the pool of useful precursors. This allows the proposal to be made that allelic exclusion may be a byproduct of cell cycle regulation during early thymocyte differentiation, which may in turn explain why the efficiency of allelic exclusion varies at different TCR or immunoglobulin loci.