Antibody: a blood protein produced in response to and counteracting a specific antigen. Antibodies combine chemically with substances which the body recognizes as alien, such as bacteria, viruses, and foreign substances in the blood.
Antibiotics: a substance produced by or a semisynthetic substance derived from a microorganism and able in dilute solution to inhibit or kill another microorganism.
Antigen: a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.