The complement system is made up of about 25 proteins that work together to “complement” the action of antibodies in destroying bacteria. Complement proteins circulate in the blood in an inactive form. When the first protein in the complement series is activated— typically by antibody that has locked onto an antigen—it sets in motion a domino effect. Each component takes its turn in a precise chain of steps known as the complement cascade. The end product is a cylinder inserted into—and puncturing a hole in—the cell’s wall. With fluids and molecules flowing in and out, the cell swells and bursts.
Template drawing and caption from "The Immune System", any modifcations, made by myself are released into the public domain.
<a rel="nofollow" class="external text" href="http://www.niaid.nih.gov/publications/immune/the_immune_system.pdf">The Immune System (pdf)</a>