Correlation of intracellular CD107a and perforin expression. (A) Intracellular FACS staining of CD107a, CD107b, and CD63 in combination with perforin (Pfn) in primary human NK cells (gated on CD3^–CD56^dim lymphocytes). Shown is one representative donor of 30. (B) Correlation among CD107a, CD107b, CD63, and Pfn on the population level. The Pfn mean fluorescence intensity (MFI) of cell populations acquired as in (A) was determined and plotted against the MFI of CD107a, CD107b, and CD63 for each healthy adult donor (N = 30). Linear regression was calculated according to Pearson. R² and P values are indicated.