The Common Cytokine Receptor γ Chain and the Pre-T Cell Receptor Provide Independent but Critically Overlapping Signals in Early α/β T Cell Development

Intracellular signals emanating from cytokine and antigen receptors are integrated during the process of intrathymic development. Still, the relative contributions of cytokine receptor signaling to pre-T cell receptor (TCR) and TCR-mediated differentiation remain undefined. Interleukin (IL)-7 interactions with its cognate receptor complex (IL-7Ralpha coupled to the common cytokine receptor gamma chain, gammac) play a dominant role in early thymopoiesis. However, alpha/beta T cell development in IL-7-, IL-7Ralpha-, and gammac-deficient mice is only partially compromised, suggesting that additional pathways can rescue alpha/beta T lineage cells in these mice. We have investigated the potential interdependence of gammac- and pre-TCR-dependent pathways during intrathymic alpha/beta T cell differentiation. We demonstrate that gammac-dependent cytokines do not appear to be required for normal pre-TCR function, and that the rate-limiting step in alpha/beta T cell development in gammac- mice does not involve TCR-beta chain rearrangements, but rather results from poor maintenance of early thymocytes. Moreover, mice double mutant for both gammac and pre-Talpha show vastly reduced thymic cellularity and a complete arrest of thymocyte differentiation at the CD44(+)CD25(+) cell stage. These observations demonstrate that the pre-TCR provides the gammac-independent signal which allows alpha/beta T cell development in gammac- mice. Thus, a series of overlapping signals derived from cytokine and T cell receptors guide the process of alpha/beta thymocyte development.