PM10 was collected in a Milan urban site, representative of the city air quality, during winter and summer 2006. Mean daily PM10 concentration was 48 μg m -3 during summer and 148 μg m -3 during winter. Particles collected on Teflon filters were chemically characterized and the endotoxin content determined by the LAL test. PM10-induced cell toxicity, assessed with MTT and LDH methods, and proinflammatory potential, monitored by IL-6 and IL-8 cytokines release, were investigated on the human alveolar epithelial cell line A549 exposed to increasing doses of PM. Besides untreated cells, exposure to inert carbon particles (2-12 μm) was also used as additional control. Both cell toxicity and proinflammatory potency resulted to be higher for summer PM10 with respect of winter PM10, with IL-6 showing the highest dose-dependent release. The relevance of biogenic components adsorbed onto PM10 in eliciting the proinflammatory mediators release was investigated by inhibition experiments. Polymixin B (Poly) was used to inhibit particle-bind LPS while Toll-like receptor-2 antibody (a-TLR2) to specifically block the activation of this receptor. While cell viability was not modulated in cells coexposed to PM10 and Poly or a-TLR2 or both, inflammatory response did it, with IL-6 release being the most inhibited. In conclusion, Milan PM10-induced seasonal-dependent biological effects, with summer particles showing higher cytotoxic and proinflammatory potential. Cytotoxicity seemed to be unaffected by the PM biogenic components, while inflammation was significantly reduced after the inhibition of some biogenic activated pathways. Besides, the PM-associated biogenic activity does not entirely justify the PM-induced inflammatory effects. © 2010 Wiley Periodicals, Inc.

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