NK-cell cytotoxicity and degranulation in the index case (patient A). (A-B) Resting peripheral blood mononuclear cells (PBMCs) or (C-D) PBMCs stimulated for 72 hours with IL-2 from patient A and 2 healthy adults were evaluated for cytotoxicity and degranulation toward K562 cells. (A,C) Plots show specific lysis for different effector cell to target cell (E:T) ratios in a 4-hour ⁵¹Cr-release assay. (B,D) After 2 hours of incubation at 37°C, the cells were stained with fluorochrome-conjugated anti-CD3, anti-CD56, and anti-CD107a monoclonal antibodies. Lymphocytes were gated on forward/side scatter plots, followed by gating on CD3 versus CD56 plots. Plots show CD56 versus CD107a expression on CD3⁻CD56⁺ natural killer (NK) cells. The percentage of CD107a⁺ cells is indicated. NK-cell cytotoxicity and degranulation were analyzed repeatedly in the patient. One representative experiment is shown.