Reduced hematopoietic progenitor cell activity in the bone marrow of IL-2^−/− mice. Bone marrow mononuclear cells from 5-week old SPF wild-type (+/+) or IL-2^−/− (−/−) mice were cultured in methylcellulose containing IL-3/GM-CSF/erythropoietin/stem cell factor for 11 days and the number of granulocyte/erythroid/myeloid/megakaryocytic (GEMM), granulocyte/macrophage (GM) and blast forming unit-erythroid (BFU-E) colonies counted. * P < .005 for comparison of IL-2^−/− and IL-2^+/+. The results shown were obtained from three independent experiments.