Figure 1

Apoptosis mediated by death receptors of the TNF family in type I and type II cells. Apoptosis can be initiated by two alternative pathways: in type I cells the amount of initiator caspases is sufficent to induce executioner caspases directly or in type II cells the enhancing effect of mitochondria is necessary. Active executioner caspases cleave the death substrates, which results in apoptosis.