Effects of 0.60 PPM nitrogen dioxide on circulating and bronchoalveolar lavage lymphocyte phenotypes in healthy subjects

Nitrogen dioxide (NO2) is a common oxidant air pollutant. Animal studies have suggested that NO2 exposure causes a decrease in the numbers of some splenic lymphocyte subtypes and impairs lymphocyte-dependent immune responses. To investigate whether ambient levels of NO2 alter circulating and bronchoalveolar lavage fluid (BALF) human lymphocytes, we studied five healthy nonsmoking adult volunteers. In each subject, blood and bronchoalveolar lavage fluid was obtained and then, more than 2 weeks later, volunteers were exposured to 0.60 ppm NO2 for 2 hr with intermittent light to moderate exercise on 4 separate days within a 6-day period. We measured standard tests of pulmonary function (airway resistance, thoracic gas volume, maximal expiratory flow) and had the subjects rate the severity of respiratory symptoms before and after each NO2 exposure. Circulating and BALF lymphocytes were labeled with fluorochrome-conjugated monoclonal antibodies to human lymphocyte antigens and a flow cytometer was used to count lymphocyte subtypes. Neither any single day's exposure nor all four exposures caused a change in symptoms or in the results of tests of pulmonary function. The total number of circulating lymphocytes obtained after NO2 exposure was slightly greater than at baseline (1792 +/- 544 vs 1598 +/- 549 cells/mm3 at baseline; P = not significant) but the proportions of lymphocyte subtypes did not differ. In the BALF obtained after NO2 exposure and in the baseline state, the total number of lymphocytes and the percentages of T cells (CD 3), B cells (CD 20), T cytotoxic-suppressor cells (CD 8), T helper-inducer cells (CD 4), and large granular lymphocytes (CD 57) also did not differ after NO2 exposure. A slightly but significantly greater proportion of natural killer cells (CD 16) was found in the BALF obtained after NO2 exposure (7.2 +/- 3.1 vs 4.2 +/- 2.4% of total lymphocytes). We conclude that repeated exposures of healthy nonsmoking adults to 0.60 ppm NO2 are not associated with clinically significant symptoms, changes in airway caliber, or alterations in circulating and BALF lymphocyte subtypes. We suggest that brief, daily exposures to NO2 at levels higher than those achieved in urban atmosphere are unlikely to provoke acute respiratory impairment in healthy, nonsmoking adults.