Aberrant expression of CD23 on B cells and impaired production of IFN-γ and IL-10 by CD4⁺ T cells from STAT3 mutant patients suggests dysregulated IL-4 signaling in HIES. Expression of CD23 on ex vivo isolated naive (A; CD20⁺CD27⁻) and memory (B; CD20⁺CD27⁺) B cells from healthy donors (open black histogram) and HIES patients (solid gray histogram) was determined by flow cytometry. Panels A and B are representative histograms; the values are the mean fluorescence intensity plus or minus SEM of CD23 on naive and memory B cells from 5 controls and 4 HIES patients. (C,D) CD4⁺ T cells isolated from a normal donor (■) and HIES patient (□) were cultured for 5 days with immobilized anti-CD3 mAb in the absence or presence of IL-2, soluble anti-CD28 mAb, or IL-21. Secretion of (C) IFN-γ and (D) IL-10 was determined after 5 days of culture. The values represent the means plus or minus SD of triplicate cultures.