APAF1 and viral infectious disease: In addition, the permeability of the outer mitochondrial membrane is increased in the context of viral infections or other death stimuli, resulting in the release of cytochrome C and binding to apoptotic protease activating factor-1 (Apaf-1) to form apoptotic bodies, thereby causing the activation of caspase-9 to cleave pro-caspase-3 and triggering pyroptosis.