Antigen

Antigens are molecules found on the surface of cells and viruses that trigger an immune response in the body. The immune system recognizes antigens as foreign and produces antibodies to neutralize or destroy them. Antigens can be proteins, carbohydrates, lipids, or nucleic acids.

Epitope

An epitope is a small, specific region on the surface of an antigen that is recognized by the immune system. Also known as an antigenic determinant, an epitope is a part of the antigen that interacts with antibodies or T cells. Different epitopes can elicit different immune responses and may be targeted by different types of antibodies.