Basophil-like c-kit⁻ FcεRI⁺ cells predominate in Ik^−/− IL-3 bone marrow cultures. Bone marrow cells from Ik^+/+ and Ik^−/− mice were cultured in IL-3 (5 ng/mL). (A) The c-kit and FcεRI expression assessed at day 19 of culture. (B) Ratio of percentage of mast cells (c-kit^hi FcεRI⁺) to basophils (c-kit⁻ FcεRI⁺) over time in wild-type and Ik^−/− cultures. Results are representative of 8 experiments with independent bone marrow cultures. (C) c-kit and FcεRI expression in cultured bone marrow cells at day 28 of culture. (D) Ik^+/+ c-kit^hi FcεRI⁺ cells (top panel), Ik^−/− c-kit⁺ FcεRI⁺ (middle panel), and Ik^−/− c-kit^– FcεRI⁺ cells (bottom panel) were analyzed for expression of markers that define the basophil phenotype (2B4⁺ CD11b⁺ Thy1.2⁺ IL3Rα^hi, solid lines). Shaded peaks: isotype control antibody. (A-D) Representative of 3 experiments with independent bone marrow cultures. (E) Wright-Giemsa staining of fluorescence-activated cell sorted Ik^−/− c-kit^– FcεRI⁺ cells (original magnification ×100), representative of 2 experiments. (F) Quantitative RT-PCR analysis of mast cell and basophil lineage-specifying genes in whole Ik^+/+ and Ik^−/− cultures. Data are the mean of 3 separate quantitative RT-PCR analyses ± standard deviation using RNA isolated from the same bone marrow culture. *P < .05. (G) Kinetics of lineage-determining gene expression assessed by quantitative RT-PCR analysis in IL-3 only Ik^+/+ and Ik^−/− cultures. Data represents mean of quadruplicates at each time point ± standard error of the mean, representative of 2 experiments.