Cytotoxicity of cigarette smoke total particulate matter (PM) in HUVECs. Following a 24-hour exposure to the indicated concentration of PM, cell viability was assessed using neutral red uptake assays. Experiments were performed in triplicate in a single HUVEC donor, and data are representative of those obtained in 3 other donors. Data are presented as mean ± S.D. cell viability. Levels are normalised to the viability of cells not exposed to PM. *p < 0.05 compared to controls.