Time course of gene expression after direct and bystander irradiation. (a) Heatmap showing mean relative gene expression of genes with characteristic biphasic expression, irradiated (I) and bystander (B) ratios are shown adjacently over the time course. On the scale bar, red indicates up-regulation and green, down-regulation of mRNA compared to controls. qRT-PCR was used to monitor expression of IL6 (b), MMP1 (c) and CXCL5 (d), at 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours and 24 hours after direct irradiation (closed circles) and bystander (closed square) exposure of IMR-90 cells. Gene expression was normalized to PPIA and UBC mRNA levels and is relative to expression in time-matched controls (dashed black line). Points are the mean and standard error of four independent experiments.