An antibody is made up of two heavy chains and two light chains. The variable region, which differs from one antibody to the next, allows an antibody to recognize its matching antigen.
Template drawing from "The Immune System", any modifications 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>