Abnormal IL-2^−/− bone marrow hematopoietic progenitor cell activity in LTBMC. Adherent stromal cell layers established from bone marrow cells of normal adult C57BL.6 mice were seeded at day 0 with 1.2 × 10⁷ bone marrow cells from 3-week old SPF wild-type (•) or IL-2^−/− (+) mice in the presence (dashed lines) or absence (solid lines) of 100 U/mL recombinant IL-2. At the times indicated, the cultures were 100% depopulated and the number and type of progenitor cells present identified by methylcellulose CFU assays as described in Materials and Methods. The results shown are representative of three independent experiments. CFU-GM, colony forming unit-granulocyte/macrophage; CFU-GEMM, colony forming unit-granulocyte/erythroid/myeloid/megakaryocyte.