Complement component 5 (C5) is part of the complement system and the body’s innate immune system. The complement system is important for controlling inflammation, homeostasis, and defending the body against foreign pathogens. C5 is cleaved into C5a and C5b by C5 convertase. C5a increases blood vessel permeability and attracts inflammatory cells, while C5b binds with other complement components to form a membrane attack complex (MAC) that kills the pathogen.1
Patients with paroxysmal nocturnal hemoglobinuria are deficient in CD59, a part of the complement system that protects normal blood cells from the MAC. Blocking C5 cleavage has been shown to inhibit the formation of MAC and limit hemolysis in these patients.2
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CD: cluster of differentiation.
1. National Center for Biotechnology Information. Complement C5 [Homo sapiens (human)]. https://www.ncbi.nlm.nih.gov/gene/727. Accessed 4/6/2019. 2. Brodsky RA. Paroxysmal nocturnal hemoglobinuria. Blood. 2014;124(18):2804-2811.