CD59 and cancer: Furthermore, complement-induced cytolytic effector mechanisms on the surface of host cells is prevented through the expression of complement regulatory proteins (CRPs), such as CD46, CD55, CD59 and factor H. Several cancer types overexpress CRPs and make use of this defense mechanism against complement-induced cytolysis (123–125), whereas downregulation or blockade of CRPs sensitizes cancer cells to complement- and antibody-mediated cytotoxicity (126, 127).