The complement membrane attack complex is a pore that inserts into the cell membrane. The complex is formed by up to 18 C9 subunits (purple), the C5, C6, and C7 subunits (various shades of green), and the C8-alpha, C8-beta, and C8-gamma subunits (shades of red). Side (left) and Top (center) views show the complex's split-washer configuration. C8 subunits bind the C9 ring with the remainder of the complex. Ultra-rare mutations (right, depicted in yellow) in C8-alpha at arginine 444 and in C8-beta at residue aspartic acid 382 appear to either stabilize or destabilize the membrane attack complex. Changes in the stability of the membrane attack complex may lead to chronic inflammation of the retina.