Milan is one of the biggest cities in Italy characterized by a heavy automotive traffic. Air pollution is a deal of concern owing to the high concentration of particulate matter (PM10 and PM2.5) registered all over the year. Existing epidemiological data suggest an impact of PM on human health; however, experimental data on the biological effects of PM are still poorly investigated. In vitro results obtained after exposure to PM10 and PM2.5 sampled in Milan during winter and summer are reported

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... here. PMs were characterized for their chemical and microbiological composition and tested to evaluate their potential toxicity in the human pulmonary cell line A549 and in the monocytes cell line THP-1. The chemical and microbiological analysis showed an evident seasonality in PM properties. Interestingly summer PMs contains mainly gram negative bacterial population while winter PMs gram positive, spore forming and possibly pathogenic, bacteria. PMs triggered different biological responses which are possibly related to the sampling season. Summer PMs elicited a higher pro-inflammatory potential that correlates to the high content of gram negative bacteria as detected by the microbiological characterization. On the other hand the winter PMs are able to induce cell cycle arrest, disrupting the normal microtubule organization in mitotic cells. The results obtained underline that the chemical properties of the PM are only in part responsible for the biological responses, since the biological components are of primary importance triggering endpoints such as inflammation.