What is an antigen?

An antigen is a molecule that is capable of inducing an immune response. This means that when it enters the body, the immune system recognizes it as a foreign substance and begins to respond against it. Antigens can be proteins, polysaccharides, or other types of molecules found on the surface of pathogens such as bacteria and viruses, as well as on other foreign substances. When the immune system identifies an antigen, it produces specific antibodies or activates other immune cells to neutralize or destroy the invader.

Understanding the role of antigens is crucial in the context of immunology and vaccine development, as vaccines often contain harmless versions or components of antigens to stimulate an immune response without causing disease. This primes the immune system to respond quickly and effectively if it encounters the actual pathogen in the future.