Freshly isolated NK cell cytotoxicity and degranulation in FHL3 patients carrying the intron 1 mutation or the 253-kb inversion. Resting PBMCs (A-B) or PBMCs stimulated with IL-2 for 48 hours (C-D) from healthy adult and infant donors or FHL3 patients were evaluated for cytotoxicity and degranulation toward K562 cells. (A,C) NK cell cytotoxicity was evaluated in a 4-hour ⁵¹Cr-release assay. Plots represent lytic units calculated at 25% lysis. (B,D) NK cell degranulation was evaluated in a 2-hour flow cytometric assay. The cells were stained with fluorochrome-conjugated anti–CD3, anti–CD56, and anti–CD107a mAbs. Lymphocytes were gated on forward/side scatter plots, followed by gating on CD3 versus CD56 plots. Plots represent induced CD107a surface expression (ΔCD107a⁺) on CD3⁻CD56⁺ NK cells. Boxes represent 25th, 50th, and 75th percentiles; pluses, mean values; and error bars, 95% CI. For FHL3 patients, each point represents one person. Intron 1 mutant alleles (blue), inversion alleles (red), and alleles with other mutations (gray) are indicated. Bars represent mean and 95% CI.