High levels of nitrogen dioxide (NO₂) are associated with asthma related morbidity and mortality although the precise mechanisms surrounding this remain unclear. This study evaluated the effects of in vivo NO₂ exposure on expression of a variety of biomarkers.

Twelve non-asthmatic subjects were randomly exposed, with an intervening 3 week period, to 2 ppm NO₂ or filtered air on four successive days. Bronchial biopsies were taken after exposure and subsequently immunostained and their expression quantified using computerised image analysis. Expression of IL-5, IL-10, IL-13, and ICAM-1 were significantly greater (p⩽0.05) in subjects exposed to NO₂ than in those exposed to filtered air.

The study showed that NO₂ exposure results in an upregulation of pro-allergic Th2 cytokines. This suggests a mechanism by which environmental agents may trigger changes in bronchial epithelium which are associated with the asthmatic inflammatory process. In turn, this raises the possibility of future targets for disease prevention and treatment. Larger studies in asthmatic subjects incorporating the effects of more long term NO₂ exposure on cytokines in conjunction with parameters such as lung function, airway hyperresponsiveness, and inflammatory surrogates are required.