CD59 is a widely expressed membrane regulatory protein, and its C-terminus is fixed on the cell surface via a GPI anchor. CD59 has different names due to its functions, such as homologous restriction factor-20, protectin and membrane inhibitor of reactive lysis (MIRL). The main physiological function of CD59 is to prevent the complement membrane attack complex (MAC) from lysing and destroying cells of the same species or its own, that is, homologous species restriction (HSR).