Effect of smoking on natural killer cell activity in the lung.

We investigated the effect of smoking on natural killer (NK) cell activity and distribution in bronchoalveolar lavage fluid (BALF) and blood. Initially, BALF NK cell activity was lower than the blood NK cell activity both in non-smokers (NS) and smokers (S). Following 24 hour culture, NK cell activity markedly increased in NS but not in S. Percentage distribution of Leu-7+ cells and Leu-11+ cells in BALF was similar in NS and S. But the BALF NK cell activity was significantly augmented by IL-2 or OK-432 (a streptococcal preparation) in NS. It appears that smoking reduces NK cell activity in BALF. It is conceivable that the low NK cell activity in BALF in S might contribute to increased incidence of infection and malignancy in smokers.