Effects of nitrogen dioxide exposure on human host defense

Nitrogen dioxide (NO₂) exposure has been linked with increased respiratory illness and infection. The objective of this study was to determine whether exposure at peak indoor levels causes airway inflammation or impairs local or systemic host defense in humans either immediately or 18 h after exposure. In an initial phase, 12 volunteers were exposed to purified air or a targeted concentration of 2.0 ppm NO₂ for 6 h, with intermittent exercise, and underwent bronchoalveolar lavage (BAL) 18 h after exposure. In a second phase, 12 volunteers participated in an identical exposure protocol but BAL was performed immediately after exposure. Eighteen hours after exposure to NO₂, polymorphonuclear leukocytes recovered by BAL increased from 2.2 ± 0.3 to 3.1 ± 0.4% (p = .005) and small decreases were found in the percentage of blood CD8⁺ T lymphocytes (p = .01) and in blood T lymphocytes expressing neither CD4 nor CD8 (p = .03). These variables were not significantly different immediately after NO₂ exposure. Nitrogen dioxide exposure did not alter lymphocyte subsets in BAL or alveolar macrophage function at either time point. Exposure to 2.0 ppm NO₂ for 6 h with exercise causes airway inflammation and may alter blood lymphocyte populations 18 h after exposure.