CD107a surface expression on NK cells, on target interaction, identifies the Munc13-4 defect. (A) PBMCs from a representative healthy donor, a patient with FHL2 (UPN 314), and 2 patients with FHL3 (UPNs 293 and 336) were cultured overnight in the presence of IL-2 and then cocultured with K562. (B-D) Polyclonal-activated NK-cell populations derived from the same donors were cocultured with FO-1 (B), 221 (C), and P815 with anti-NKp30 (D) mAbs. Cells were stained with anti–CD56-PC5 mAb and anti–CD107a-PE mAb and then analyzed by double fluorescence gating on CD56⁺ cells. Numbers indicate the percentage of CD107a⁺ cells. In panel E, histograms refer to the percentage of CD107a⁺ cells (▦) and to the mean fluorescence intensity (MFI) of CD107a surface expression (▪) considering CD56⁺ cells in a group of patients with FHL3 (mean of 6 ± SD) compared with healthy individuals (mean of 9 ± SD) and patients with FHL2 (mean of 3) after coculture with susceptible target cells. In patients with FHL3, both percentage and MFI were significantly lower than in healthy controls (P < .001; Student t test). Patients with FHL3 are also shown individually.