CASP9 and infection: Next, the activities of caspase 8 and caspase 9 on infection with either H37Ra or H37Rv were monitored at 24 hrs of infection, using calorimetric assay, and we found that the expression level of caspase 8 was reduced to 50% (0.8 ± 0.3) in host cells infected with H37Rv.