Basophils were responsible for the augmented IL-4 production by IRF-2–deficient spleen cells. (A) IL-3–induced IL-4 production by whole spleen cells isolated from control (○) or IRF-2^-/- mice (•). Each symbol represents an individual mouse. Horizontal bars are the means. Amounts of IL-4 produced are significantly higher for IRF-2^-/- mice than for controls (P < .005). (B) Flow cytometry for basophil-enriched (Bs(+)) or depleted (Bs(-)) spleen cells. Numbers represent the percentages of basophils. (C) IL-3–induced IL-4 production by the cell preparations shown in panel B. ND indicates not detectable (< 20 pg/mL). Repeated 3 times with similar results. Means and SD of duplicate cultures established with cells from control (□) or IRF-2^-/- mice (▪) are shown.