Reduced generation but efficient TCR beta-chain selection of CD4(+)8(+) double-positive thymocytes in mice with compromised CD3 complex signaling

Maturation to the CD4(+)8(+) double-positive (DP) stage of thymocyte develo pment is restricted to cells that have passed TCR beta selection, an import ant checkpoint at which immature CD4(-)8(-) double-negative (DN) cells that express TCR beta polypeptide chains are selected for further maturation. T he generation of DP thymocytes following TCR beta selection is dependent on cellular survival, differentiation, and proliferation, and the entire proc ess appears to be mediated by the pre-TCR/CD3 complex. In this study, we in vestigate the signaling requirements for TCR beta selection using mice sing le deficient and double deficient for CD3 zeta/eta and/or p56(lck), While t he numbers of DP cells are strongly reduced in the single-deficient mice, a further drastic reduction in the generation of DP thymocytes is seen in th e double-deficient mice. The poor generation of DP cells in the mutant mice is primarily due to an impaired ability of CD25(+) DN thymocytes to prolif erate following expression of a TCR beta-chain, Nevertheless, the residual DP cells in all mutant mice are strictly selected for expression of TCR bet a polypeptide chains. DN thymocytes of mutant mice expressed TCR beta and C D3 epsilon at the cell surface and contained mRNA for pre-T alpha, but not for clonotypic TCR alpha-chains, together suggesting that TCR beta selectio n is mediated by pre-TCR signaling in all cases. The data suggest different ial requirements of pre-TCR signaling for cell survival on the one hand, an d for the proliferative burst associated with TCR beta selection on the oth er.