MAC, Human, mAb B7

The monoclonal B7 antibody (HM2443) recognizes a C9 epitope of the membrane attack complex (MAC). The three distinct activation pathways of complement converge with the formation of a C3 convertase and subsequently C3b. This initiates the formation of the C5 convertase. The cleavage of C5 by this convertase initiates the lytic or terminal pathway. In contrast to the three activation pathways, which require enzymatic cleavage for activation, the terminal pathway relies on conformational changes induced by binding. Binding of C6 to C5b facilitates binding of C7 which alters the conformation of the complex. After binding of C8, a variable number of C9 molecules associates to the C5b-8 complex to form C5b-9, which is also termed as MAC. The formation of MAC causes lysis of cells when the incorporated C9 molecules of the complex unite into a pore-forming structure. The B7 antibody can be used to stain C5b-9 (or MAC) deposition in tissues and can recognize both C9 and soluble C5b-9 (sC5b-9/TCC) in fluid-phase matrices, like serum or plasma.