There are a number of caspases in mammalian cells that have been shown to be involved in the early stages of apoptosis, e.g. Caspase 2, Caspase 3, Caspase 6, Caspase 7, Caspase 8, Caspase 9 and Caspase 10. The functions of these enzymes are not yet entirely clear, but it appears that after an initial signal to the cell to undergo apoptosis, they may be responsible for the activation, amplification and execution of the apoptotic cascade. Because of the central importance of the caspases in apoptosis, their detection by flow cytometry has become widespread. The activity of enzymes implicated in apoptosis may be detected in three ways: