CASP8 and infection: In contrast to infection with ΔospD3, infection with ΔospC1ΔospD3 did not increase the levels of phosphorylation of MLKL or cytotoxicity, whereas caspase-8 activity was elevated in cells infected with ΔospC1 or ΔospC1ΔospD3 (Fig. 6D,E).