The <a href="https://en.wikipedia.org/wiki/complement_system" class="extiw" title="w:complement system">complement system</a> 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.
<ul><li>English text of 'Image:Complement pathway.png' by <a href="//commons.wikimedia.org/wiki/User:DO11.10" title="User:DO11.10">DO11.10</a></li>
<li>German translation of 'Image:Complement pathway.png' by  <a href="//commons.wikimedia.org/wiki/Special:Contributions/Hduman" title="Special:Contributions/Hduman">Hduman</a></li>
<li>Galician translation <a href="//commons.wikimedia.org/wiki/User_talk:Miguelferig" title="User talk:Miguelferig">Miguelferig</a></li>
<li>Catalan translation <a href="//commons.wikimedia.org/wiki/User:Leptictidium" title="User:Leptictidium">Leptictidium</a></li>
<li>Spanish translation <a href="//commons.wikimedia.org/wiki/User:Asierog" title="User:Asierog">Asierog</a></li>
<li>SVG by <a href="//commons.wikimedia.org/wiki/User:Perhelion" title="User:Perhelion">Perhelion</a></li></ul>
Own work based on: <a rel="nofollow" class="external free" href="http://www.niaid.nih.gov/publications/immune/the_immune_system.pdf">http://www.niaid.nih.gov/publications/immune/the_immune_system.pdf</a>