Effect of tumour cell contact on endothelial cell OPG production. HuDMECs were co-cultured with the T47D cell line at HuDMEC: T47D ratios of 2:1, 4:1 and 10:1 for 72 hours as described in materials and methods. HuDMECs were separated from the T47D cell line and gene expression measured in the separate cell populations using real-time quantitative PCR (a). OPG secretion was assessed using ELISA (b). For real-time quantitative PCR, values were normalised to GAPDH and are given as fold expression compared to untreated HuDMECs. Data are represented as mean ± S.E.M. from three independent experiments. ***, p < 0.001 compared to control cells (HuDMEC only); **, p < 0.01 compared to control.