Ik^−/− mice exhibit increased basophils in the absence of infection. (A) Proportion of c-kit⁻ FcεRI⁺ cells in indicated tissues of naive Ik^+/+ and Ik^−/− mice assessed by flow cytometry. Blood basophils were evaluated for the expression of FcεRI and CD200R3 after gating on c-kit⁻ cells. Numbers denote percentage of basophils. (B) Quantification of basophil (c-kit⁻ FcεRI⁺ CD200R3⁺) and eosinophil (c-kit⁻ Ly6G⁻ Siglec-F⁺) numbers in bone marrow of wild-type and Ik^−/− mice by TruCount bead assay. P < .05 (C) Cell surface expression of basophil markers in c-kit^– FcεRI⁺ cells from Ik^−/− bone marrow determined by flow cytometry. (D) Fluorescence-activated cell sorted Ik^−/− c-kit^– FcεRI⁺ bone marrow cells were subject to quantitative RT-PCR analysis to assess expression of lineage-specific transcription factors and proteases. Data represents mean of triplicates ± standard error of the mean. (E) Fluorescence-activated cell sorted Ik^−/− c-kit^– FcεRI⁺ cells bone marrow cells were Wright-Giemsa stained (original magnification, ×100). Results shown in panels A-B are representative of 4 (blood) and 6 (bone marrow, spleen, and liver) of mice of each genotype. (C-D) Representative of 4 mice. (E) Representative of 3 mice.