Effect of RNA synthesis inhibition on inducible defensin expression. 16HBE human epithelial bronchial cells (5 × 106) were grown in six well plates for 24 hours. The cells were then pre-treated with 1 mg of actinomycin D/ml (ActD) or DMSO solvent for 1 h, and some samples were then exposed to the different morphotypes of A. fumigatus either for 6 (Figure 7A) or for 18 (Figure 7B) hours. There was no significant difference in viability between control and treated cells as assessed by staining with trypan blue. Furthermore, the yields of total RNA from the samples were compared and showed no difference. Total RNA was extracted and analysed by RT-PCR. The sizes of amplified products are indicated and were as predicted. GAPDH was uniformly expressed. Complete inhibition of hBD2 and hBD9 expression by the cells exposed to A. fumigatus, either for 6 or for 18 hours was observed after pre-treatment of the cells with actinomycin D.