Cell cycle analysis. (A) Cell cycle of BEAS-2B cells exposed to 7.5 μg/cm2 of winter PM2.5 for 1, 3, 6, 10, 24 and 40 h. The results are representative of 4 independent experiments. (B) Mitotic cells scoring: BEAS-2B cells, exposed for 3, 10, 24 and 40 h to 7.5 μg/cm2 of winter PM2.5, were stained for DNA and β-tubulin and scored as interphasic, mitotic or apoptotic cells. The results are representative of 3 independent experiments; in each experiment 500 cells were scored. * Statistically significant difference from untreated cells (control), P < 0.05.