| Abstract: | The β chain (p75) of the interleukin-2 (IL-2) receptor (IL-2R) is expressed on up to 5-7% of fetal thymocytes on day 16 of gestation, declining thereafter to a minute proportion of less than 1% around birth, and of 1-2% of adult thymocytes. A significant part of fetal IL-2R β+ thymocytes are γδ cells. The precursor-progeny relationships of fetal DL-2Rβ+ thymocytes to the αδ T cell lineage have not been previously studied, nor has their position within the developmental sequence been determined. Here we show that IL-2Rβ is expressed on a subset of very immature cells, along with high amounts of Pgp1 and FCγRII/III, partially preceding the expression of intracellular CD3?. IL-2-Rβ disappears before expression of IL-2Rα. IL-2Rβ+ cells, purified by sorting on day 15 of gestation, efficiently reconstituted fetal thymic lobes depleted of lymphoid cells by treatment with desoxyguanosine. They developed into T cell receptor (TCR)αβ+, TCRγδ+, and CD4/CD8 double- and single-positive cells in similar proportions as did sorted IL-2Rα+ day 15 fetal thymocytes. These data suggest that IL-2Rβ expression marks a short period of very early thymocyte development, perhaps immediately after entry into the thymus. |
