Regulation of T cell receptor (TCR) β gene expression by CD3 complex signaling in immature thymocytes:: Implications for TCRβ allelic exclusion

During alpha beta thymocyte development, clonotype-independent CD3 complexes are expressed at the cell surface before the pre-T cell receptor (TCR), Signaling through clonotype-independent CD3 complexes is required for expression of rearranged TCR beta genes, On expression of a TCR beta polypeptide chain, the pre-TCR is assembled, and TCR beta locus allelic exclusion is established, We investigated the putative contribution of clonotype-independent CD3 complex signaling to TCR beta locus allelic exclusion in mice single-deficient or double-deficient for CD3 zeta/eta and/or p56(lck). These mice display defects in the expression of endogenous TCR beta genes in immature thymocytes, proportional to the severity of CD3 complex malfunction. Exclusion of endogenous TCR beta VDJ (variable, diversity, joining) rearrangements by a functional TCR beta transgene was severely compromised in the single-deficient and double-deficient mutant mice. In contrast to wild-type mice, most of the CD25(+) double-negative (DN) thymocytes of the mutant mice failed to express the TCR beta transgene, suggesting defective expression of the TCR beta transgene similar to endogenous TCR beta genes. In the mutant mice, a proportion of CD25+ DN thymocytes that failed to express the transgene expressed endogenous TCR beta polypeptide chains. Many double-positive cells of the mutant mice coexpressed endogenous and transgenic TCR beta chains or more than one endogenous TCR beta chain. The data suggest that signaling through clonotype-independent CD3 complexes may contribute to allelic exclusion of the TCR beta locus by inducing the expression of rearranged TCR beta genes in CD25(+) DN thymocytes.