Effect of ascorbic acid on human natural killer cells.

Ascorbic acid (vitamin C) was found to inhibit human natural killer cell (NK cell) activity in a dose-dependent manner. Neither effector/target cell binding nor interferon (IFN)- or interleukin-2 (IL-2)-induced increases of NK activity were affected by vitamin C. Lymphocytes incubated for 1 h at 4 degrees C with vitamin C showed a normal NK activity, whereas lymphocytes incubated for 1 h at 37 degrees C with vitamin C exhibited low NK activity. Our findings suggest that vitamin C influences NK cells, probably by acting as a radical scavenger which inactivates killing factors of NK cells.