Antigen
Any molecule, such as a protein or carbohydrate on a pathogen or cell surface, that the immune system recognizes as foreign and that triggers an antibody or cellular immune response. Antigens are central targets for vaccines and diagnostic assays.
What is an antigen?
An antigen is any molecule that the immune system recognizes as foreign and responds to, commonly a protein or carbohydrate found on the surface of a virus, bacterium, or other cell. The specific region of the antigen that an antibody actually binds is called an epitope.
When the immune system encounters an antigen, it can mount a response that includes producing antibodies tailored to that antigen and activating immune cells to eliminate the threat. In this sense antigens are the triggers that set adaptive immunity in motion.
Why are antigens important?
Antigens are central to how vaccines work: by exposing the body to a harmless form or fragment of an antigen, a vaccine teaches the immune system to recognize and react quickly to the real pathogen later. The choice of antigen largely determines what protection a vaccine provides.
They are equally important in diagnostics, where many tests detect either an antigen itself or the antibodies the body has made against it. This makes antigens a shared foundation for prevention, detection, and a great deal of immunology research.
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