- Inhalation of traffic-associated atmospheric particulate matter (PM2.5) is recognized as a significant health risk. In this study we focused on a single ("sub-clinical response") exposure to water-soluble extracts from PM collected at a roadside site in a major European city, to elucidate potential components that drive pulmonary inflammatory, oxidative and defense mechanisms, and their systemic impacts. Intra-tracheal instillation (IT) of the aqueous extracts induced a 24h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-α), increased reactive oxygen species production, but insignificant lipids and proteins oxidation adducts in mice' lungs. This local response was largely self-resolved by 48h, suggesting that it could represent a sub-clinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary PM-mediated response. An artificial metal solution (MS) recapitulated the PM extract response. The self-resolving nature of the response is associated with activating defense mechanisms (increased levels of catalase and glutathione peroxidase expression), observed with both PM extract and MS. In conclusion, metals present in PM collected near roadways are largely responsible for the observed transient local pulmonary inflammation and oxidative stress. Simultaneous activation of the antioxidant defense response may protect against oxidative damage.