A Y-shaped protein found in the blood and produced by the B-cells of the body’s immune system in response to an invading foreign substance or antigen. Antibodies protect the body from disease by binding to these invaders and destroying them.
A lock and key analogy is often used to describe the shapes of the antibody and antigen. The antigen is the key, hoping to enter into and infect a cell. The antibody is the lock that grips and locks the key, preventing it from entering and infecting cells. These locks (the antibodies) are what our immune system has manufactured to keep recognizing and “locking in” the antigen so that it cannot harm the body.
See the monoclonal antibody.