Stimulus-dependent inhibition of NK-cells by CML cells: reversal by histamine and catalase.

One hundred thousand heterologous NK cell-enriched lymphocytes were admixed with 1.2 to 5 × 10⁴ CML cells and assayed for cytotoxicity against K562 cells (10⁴ cells/well) in a 16-hour assay. The cell cultures were treated with culture medium (control, ○), histamine (10 μmol/L, ●), or catalase (100 U/mL, ▪). The right part of the figure shows data obtained in cell cultures also treated with fMLF (0.1 μmol/L), added at 15 minutes after the onset of incubation. Data are cell lysis percent ± SEM of sextuplicate determinations.