Natural killer cell tumoricidal activity in cigarette smokers and in silicotics

Cigarette smoking and asbestos exposure have been reported to alter the tumor-killing activity of blood natural killer (NK) cells. However, NK cell function in relation to silica dust exposure has not been examined. We studied blood NK cell number, percentage, and tumoricidal activity in 120 hardrock miners, 57 of whom had radiographic evidence of silicosis, and in 33 community controls. There was a significant increase in leukocyte count and lymphocyte count in current smokers compared with former and never smokers, but these cell counts were normal in silicotics and those with silica dust exposure. No significant differences in NK cell (CD16+) number or percentage were found by flow cytometric analysis of smoking or dust exposure groups. Surprisingly, NK tumoricidal activity was significantly higher in cigarette smokers compared with former smokers and never smoker control subjects. Although tumoricidal activity was elevated in silicotics, this was accounted for by their cigarette smoking. These results suggest that cigarette smoking is associated with elevation of blood NK cell tumoricidal activity on a per cell basis, in the absence of any alteration in the absolute number of NK cells in blood.