Interleukins 2 and 3 regulate the in vitro proliferation of two distinguishable populations of 20-α-hydroxysteroid dehydrogenase-positive cells

The ability of interleukin 2 (IL 2), interleukin 3 (IL 3), and granulocyte/macrophage colony-stimulating factor (GM-CSF) to induce the proliferation of cells from thymus, spleen, or bone marrow was examined and compared with their ability to induce expression of the enzyme 20-α-hydroxysteroid dehydrogenase (20αSDH). In the thymus, the peanut agglutinin agglutinated cells (PNA⁺) lacked 20αSDH and showed no detectable response to IL 2, IL 3, or GM-CSF in either proliferation or induction of 20αSDH. In contrast, the PNA nonagglutinated (PNA^-) subpopulation expressed 20αSDH and proliferated in response to Con A and/or IL 2. The responding cells that could be expanded in vitro with IL 2 expressed high levels of 20αSDH. Neither IL 3 nor GM-CSF in the presence or absence of Con A had a demonstrable effect on the PNA^- population. In cultures of bone marrow cells, both IL 3 and GM-CSF induced proliferation, whereas IL 2 had no effect of proliferation in the presence or absence of Con A. Thy-1-depleted bone marrow cells, expanded in tissue culture with IL3, contained cells that co-expressed Thy-1 and 20αSDH. In contrast, cells proliferating in vitro to GM-CSF did not express Thy-1 or 20αSDH. In cultures of normal splenic lymphocytes, two populations of cells capable of expressing 20αSDH were detected. One population could be expanded in vitro with IL 2 and Con A, whereas the second was responsive to IL 3. In spleens from athymic mice, only the latter cells were detected. These results demonstrate that IL 3 and IL 2 responsiveness distinguishes two populations of 20αSDH cells. The relevance of these observations to the possible relationship of IL 3 and IL 2 in T cell differentiation is discussed.