An antibody is a large, Y-shaped protein produced when an antigen—a toxic or foreign substance—is detected by macrophages, the cells that ingest and degrade invaders. Each antibody binds to one specific antigen, either disabling it directly or signaling to the rest of the immune system to eliminate the molecule. Antibodies are part of the adaptive immune system. For more science in your inbox, sign up for our newsletter: Elysiumhealth.com | Elysium Health | Facebook