The C5-9 membrane attack complex is formed by the activation of C5 to form C5b by either the classical or alternative pathways. C5b sits in the target cell membrane and sequentially binds C6 to C8. The new complex then binds 8 or 9 molecules of C9 which compose the walls of a pore spanning the target cell membrane.
The pore permits small molecules to pass to the inside with subsequent lysis of the target cell.
The membrane attack complex also has other less important functions:
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