Analysis of the variability in cytotoxic lymphocyte exocytosis in healthy adults. (A-H) PBMCs from 198 healthy adult volunteers were incubated for 3 hours in medium or with target cells and mAbs as indicated. (A) Graph displays levels of exocytosis in CD8⁺CD57⁺ T cells or CD3^–CD56^dim NK cells stratified according to CMV serostatus. Boxes and whiskers display quartiles, limits, as well as outliers, with plus signs representing means. Pairs statistically different by Student t test are indicated. (B) Flow cytometry plots show CD3^–CD56^dim NK-cell CD107a surface expression in relation to intracellular expression of FcεRγ or EAT-2, after indicated stimulations. The percentages of cells in each quadrant are indicated. Only 5.4% of FcεRγ^– NK cells exocytosed after K562 stimulation, compared with 21.7% of FcεRγ⁺ NK cells. Similarly, 6.7% of EAT-2^– NK cells exocytosed when stimulated with K562, compared with 25% of EAT-2⁺ NK cells. (C-D) Graphs displaying the relationship between CD3^–CD56^dim NK-cell–induced CD107a surface expression and frequencies of cells lacking expression of FcεRγ, EAT-2, or SYK after stimulation with P815 cells added anti-CD16 mAb (C) or K562 cells (D). Diagonal lines represent linear regression and with 95% confidence intervals in bold, whereas the dashed horizontal line indicates the cutoff percentage deemed abnormal in regard to K562 cell–induced NK-cell exocytosis. (E) The graph depicts frequencies of CD107a-expressing NK cells according to stimulation and expression of FcεRγ, SYK, and EAT-2 in CD3^–CD56^dim NK-cell subsets, with bars representing SD. (F-H) Graphs correlating exocytic responses in cytotoxic lymphocyte subsets in healthy individuals, as specified. Donors with low CD107a response after K562 stimulation and expanded FcεRγ^– NK-cell populations are highlighted with red and orange dots, whereas donors with low CD107a responses to anti-CD3 and anti-CD16 are highlighted with blue dots.