CD59, also known as protectin, is a glycosylphosphatidylinositol （GPI）-anchored protein expressed on the surface of various cells. It plays a vital role in regulating the immune system and protecting cells from the complement system. Specifically, CD59 is the only membrane-bound inhibitor of the complement membrane attack complex （MAC）, an immune pore that can damage human cells. Without CD59, MAC pores formed on red blood cells result in rupture, causing chronic hemolysis and immune-related neuropathies.