DISTINCT ROLES OF THE INTERLEUKIN-7 RECEPTOR-ALPHA CHAIN IN FETAL ANDADULT THYMOCYTE DEVELOPMENT REVEALED BY ANALYSIS OF INTERLEUKIN-7 RECEPTOR ALPHA-DEFICIENT MICE

Mouse mutants lacking expression of the IL-7 receptor (IL-7R) alpha ch ain are defective in thymopoiesis. The adult thymus has multiple defec ts, including reduced cell numbers and proportions of the more mature thymocyte subsets, a complete absence of CD25(+) cells and a reduced l evel of RAG1 and RAG2 expression. We show here that, in contrast to th e profound developmental arrest observed in the adult thymus, fetal th ymocytes from IL-7R alpha(-/-) mice have normal proportions of all of the major thymocyte subpopulations, including CD25(+) thymocytes and t he most mature single-positive subsets. Moreover, normal levels of RAG 1 and RAG2 were observed. Total thymocyte numbers, however, remained r educed. These data suggest that the IL-7R alpha chain is a key regulat or of both survival and proliferation during thymocyte development but that it is not essential for the production of T cells during fetal t hymopoiesis.