Genetic reduction of basophil numbers in vivo restored Th2 polarization in IRF-2^-/- mice. (A) The percentages of FcϵRIα⁺B220^- cells in the spleen in mice with the indicated genotypes. Control, Kit^W-v/W-v, and IRF-2^-/- denote IRF-2^+/-Kit^W-v/+, IRF-2^+/-Kit^W-v/W-v, and IRF-2^-/-Kit^W-v/+ mice, respectively. Each symbol represents the value of an individual animal. The values for IRF-2^-/-Kit^W-v/W-v mice are significantly lower than those for IRF-2^-/- mice (P < .01) and not significantly different from those for Kit^W-v/W-v mice (P > .05). (B) IL-3–induced IL-4 production by unseparated spleen cells prepared from mice of the indicated genotypes. Values are means and SD of duplicate cultures. ND indicates not detectable (< 10 pg/mL). (C) Cytokine production by fresh splenic CD4⁺ T cells on CD3/CD28 stimulation. Values are means and SD of duplicate cultures. ND indicates not detectable (< 20 pg/mL). Representative of experiments with 4 litters.