IL-2 partially restores degranulation and cytotoxicity by PBLs from FHL4 patients. (A-E) PBLs from healthy adult and infant donors, plus FHL2, FHL3, and FHL4 patients were stimulated with 400 IU/mL IL-2 for 72 hours. (A) IL-2–stimulated PBLs were evaluated for cytotoxicity toward K562 cells in 4-hour ⁵¹Cr release assays. Lytic units were calculated from specific lysis values. (B) PBLs were maintained in medium or medium with IL-2 added for the indicated times. Thereafter, PBLs were incubated alone or with K562 cells as indicated for 2 hours at 37°C. Cells were stained with fluorochrome-conjugated anti-CD3, anti-CD56, and anti-CD107a mAbs. Induced CD107a surface expression on CD3⁻CD56⁺ NK cells after incubation with K562 cells relative to PBLs alone was plotted as a function of stimulation time with IL-2. (C-E) PBLs stimulated with IL-2 for 72 hours were incubated alone or with target cells as indicated for 2 hours at 37°C. Thereafter, cells were stained with fluorochrome-conjugated anti-CD3, anti-CD56, and anti-CD107a mAbs. (C) Lymphocytes were gated on forward scatter/side scatter plots, followed by gating on CD3 versus CD56 plots. Profiles show CD56 versus CD107a mAb staining of CD3⁻CD56⁺ NK cells. (D) Induced CD107a surface expression on CD3⁻CD56⁺ NK cells after indicated stimulation was plotted. Lines represent mean values. (E) Induced CD107a surface expression on lymphocytes after indicated stimulation was plotted. Lines represent mean values.