These observations are in agreement with previous findings where it was shown that MNV replication triggered apoptosis in infected RAW264.7 cells at 12–16 hours post-infection, through the activation of caspase-9, caspase-3 and was associated with a down-regulation of survivin (an inhibitor of apoptosis which prevents activation of caspase-9). This evidence concerns the gene CASP9 and infection.