CASP8 and infection: To further clarify the mechanisms involved in MO-induced apoptosis in MH-S cells, we detected the activity of the primary initiator for extrinsic apoptosis (caspase-8) and found that MO infection remarkably increased transcriptional levels of caspase-8 gene in a time-dependent manner and significantly upregulated caspase-8 expression (Figure 5a-c).