Role of the Intracellular Domain of IL-7 Receptor in T Cell Development

Signals from the IL-7R are uniquely required for T cell development and maintenance, despite the resemblance of IL-7R to other cytokine receptors and the apparent sharing of common signaling pathways. This unique requirement could either reflect unique expression of IL-7R or IL-7, or it could indicate that the IL-7R delivers unique signals. To determine whether the IL-7R provided unique signals, we exchanged its intracellular domain with that of other cytokine receptors: IL-4R, IL-9R, and prolactin receptor (PRLR). Chimeric receptors were used to reconstitute development of IL-7R −/− hemopoietic progenitors by transducing the receptors in retroviral vectors. Whereas IL-7R −/− thymocytes are arrested at the double-negative stage, IL-4R, IL-9R, or PRLR all imparted some progression to the double-positive stage. IL-4R and PRLR gave only small numbers of thymocytes, whereas IL-9R gave robust αβ T cell development and reconstitution of peripheral CD4 and CD8 cells, indicating that it can duplicate many of the functions of IL-7R. However, IL-9R failed to reconstitute rearrangement of the TCRγ locus or development of γδ T cells. Thus, the IL-7R signals required in the αβ T cell lineage (such as survival and proliferation) are not unique to this receptor, whereas rearrangement of the TCRγ locus may require a signal that is not shared by other receptors.