Pollutants and asthma: Role of air toxics

Asthma is a disease characterized by intermittent bronchoconstriction due to increased airway reactivity to both allergic and nonallergic stimuli. Most asthma exacerbations that result in hospitalization are associated with viral upper respiratory tract infections. Such infections typically induce T-helper type 1 (T(H)1) responses in the airway, involving activation of nuclear factor-kappaB (NF-kappaB). However, a more recently appreciated cause of asthma exacerbation is exposure to pollutants, including ozone and various components of particulate matter (PM), including transition metals, diesel exhaust, and biologicals such as endotoxin. Although the role of air toxics in asthma pathogenesis remains incompletely examined, many components of PM that are active exacerbants of asthma are also prominent air toxics (metal ions and organic residues). These agents have been observed to activate NF-kappaB. Reviewed in this article are the actions of specific air pollutants on airway inflammation in humans and potential common response pathways for ozone, PM, and several air toxics.