The absence of IL-2 causes an accumulation of immature myeloid cells in the bone marrow of IL-2^−/− mice. Cytocentrifuge preparations of bone marrow cells (BM) from 6-week old SPF wild-type (+/+) and IL-2^−/− (×/×) mice were fixed and stained with Wright-Giemsa stain before photomicroscopy. Magnification 800X. The results shown are representative of 10 groups of mice.