Caspase 9 expression. Caspase 9 expression, as measured in triplicates from triplicate monolayer cultures by qRT-PCR at 24, 72 and 144 hours post irradiation with 2 Gy and tested using Mann–Whitney U-test. Mean values are shown + SEM. The expression was calculated relative to GAPDH mRNA levels (Caspase 9/GAPDH). * = p ≤ 0.05 when comparing irradiated and non-irradiated cultures and ¤ = p ≤ 0.05 when uninfected and infected cultures are compared from the same time point.