Perforin binding on the surface of K562 and ML-2 cells.

Target cells were incubated for 4 hours with 30 μL PBS or with 100 μg total protein of the NK lysates. After 1 hour of incubation with a FITC-labeled antiperforin antibody or an FITC-labeled isotype antibody, cells were analyzed by flow cytometry. (A) K562 cells + perforin antibody, (B) ML-2 cells + perforin antibody, (C) K562 cells + isotype antibody, and (D) ML-2 cells + isotype antibody. Open histograms = cells with PBS, shaded histograms = cells with NK lysates. M1 indicates perforin-positive cells.