Caspases are a class of cysteine proteases, or a type of enzyme, that break up or cleave other proteins. Caspases are involved in the initiation and execution of apoptosis (programmed cell death). The caspases transmit intracellular signals through a "caspase cascade" where one caspase cleaves a second caspase, and this cleavage activates the second caspase. Once activated, the second caspase could then cleave other caspases (thereby activating them) or other downstream ligands.