Antigens are molecules that are found on the surface of viruses, bacteria, and other foreign bodies. They act as flags, identifying these invader cells to the body’s immune system. The body’s immune cells detect the antigens and produce antibodies against them, which then bind to the antigens and neutralize them. Antigens play an important role in the body’s immune response, triggering the production of antibodies that defend the body against infection and disease. They are also used in medical diagnostics to detect the presence of particular pathogens in a sample. The ability to identify antigens can help identify an offending microorganism and help researchers better understand how the body responds to a particular antigen.