Distinct roles of the interleukin-7 receptor α chain in fetal and adult thymocyte development revealed by analysis of interleukin-7 receptor α-deficient mice

Mouse mutants lacking expression of the IL-7 receptor (IL-7R) alpha chain are defective in thymopoiesis. The adult thymus has multiple defects, including reduced cell numbers and proportions of the more mature thymocyte subsets, a complete absence of CD25(+) cells and a reduced level of RAG1 and RAG2 expression. We show here that, in contrast to the profound developmental arrest observed in the adult thymus, fetal thymocytes from IL-7R alpha(-/-) mice have normal proportions of all of the major thymocyte subpopulations, including CD25(+) thymocytes and the most mature single-positive subsets. Moreover, normal levels of RAG1 and RAG2 were observed. Total thymocyte numbers, however, remained reduced. These data suggest that the IL-7R alpha chain is a key regulator of both survival and proliferation during thymocyte development but that it is not essential for the production of T cells during fetal thymopoiesis.