CD4⁺ T cells from HIES patients undergo normal proliferation and differentiation into Th1-, Th2-, T reg–, and T_FH-type effector cells. (A) CFSE profiles of normal (outline black histogram) and HIES (solid red histogram) CD4⁺ T cells after stimulation with CD3/CD28 mAb and IL-2 for 5 d. (B) Intracellular expression of IFN-γ and IL-2 in CD4⁺ T cells purified from normal donors and HIES patients after activation for 4–5 d with CD3/CD28/IL-2. The FACS plots in B are representative of one normal control and one HIES patient. (C and D) Frequency of CD4⁺ T cells from normal controls and HIES patients that expressed IL-2 (C) or IFN-γ (D). (E–I) Secretion of IFN-γ (E), TNF-α (F), IL-4 (G), IL-10 (H), and IL-13 (I) by normal and HIES CD4⁺ T cells stimulated with anti-CD3/CD28 mAb and IL-2 for 5 d. (J and K) CD4⁺ T cells were labeled with either (J) CD25 and CD127 to identify T reg cells (CD25^hiCD127^lo) or (K) CXCR5 to identify T_FH cells, as indicated by the gated populations. The values represent the frequency of gated cells and are from one healthy donor and one HIES patient and are representative of at least four patient and control samples. (L) PBMCs were labeled with anti-CD4 and CCR6 mAb, and the frequency of CD4⁺ CCR6⁺ cells in healthy donors and HIES patients was enumerated. For all graphs (E–I and L), each symbol represents the value from an individual donor or patient, and the line represents the mean. *, P < 0.05; **, P < 0.01; ns, not significant.