have an antiapoptotic effect against several death inducers. (A) Transmission electron microscopy of 16HBE cells treated 24 h with A23187 (3 μM) in the absence or in the presence of a 4 h pretreatment with 10 μg/cm2 PM2.5-AW. The micrographs illustrate that control or PM2.5-treated cells show normal nuclear chromatin condensation with the presence of some nucleoli (a) and normal ultrastructure of mitochondria (black arrow). PM's aggregates are localized near to the plasma membrane of cells exposed to particles or into the cytoplasm (white arrows). Treatment with A23187 alone triggered typical features of apoptotic cell death characterized by reduced cellular volume, massive chromatin condensation (b), formation of apoptotic bodies (black asterisk) and maintenance of the plasma membrane integrity. Note that PM2.5-AW pretreatment prevented A23187-induced morphological modifications and allowed 16HBE cells to retain nuclear or mitochondria morphologies similar to those of the control. Scale bar represent 5 μm. (B and C) After a 4 h pretreatment with PM2.5-AW (10 μg/cm2), 16HBE cells were exposed to different inducers of cell death for another 20 h such as mitochondrial respiratory chain inhibitors (rotenone (Rot, 5 μM), antimycin A (AMA, 25 μg/ml) and oligomycin (Omy, 5 μM)), calcium ionophores (ionomycin (Iono, 0.5 μM) and A23187, 3 μM), protein kinases inhibitor (staurosporine STS, 1 μM) and oxidative stress activator (H2O2, 500 μM). Then, cells were quantified for DiOC6(3) low or PI high staining by flow cytometry. (D and E) The human bronchial epithelial NCI-H292 cell line and NHBE primary cells were assessed by flow cytometry in the presence or the absence of PM2.5-AW pretreatement (10 μg/cm2) and apoptosis inducers: A23187 (3 μM), staurosporine (STS, 1 μM) and H2O2 (500 μM). Experiments were repeated three times, and means ± S.D. are shown. Significance was calculated with respect to untreated controls (*, p < 0.001) and with respect to non-pretreated cells with particles (#, p < 0.001).