Physical or chemical agents such as cellular toxins or hormones can also induce apoptosis. (Under or over expression of certain hormones can initiate apoptosis.) Special signaling molecules (tumor necrosis factor TNFa, FasL) can induce apoptosis by binding to their respective receptors on the cell. (This occurs when, after a search of a cells surface, a cytotoxic T cell (Tc) concludes it is damage