What is an antigen?

An antigen is defined as a substance that triggers an immune response. This can include a variety of molecules, such as proteins, polysaccharides, or even nucleic acids that are found on the surface of pathogens like bacteria and viruses, or can come from non-pathogenic sources. When the immune system detects these antigens, it responds by activating immune cells that produce antibodies specifically against the antigen, which helps to neutralize or eliminate the threat.

Understanding antigens is crucial because they are key to the functioning of the immune system and are involved in determining how the body recognizes and responds to infections and diseases. This concept is also foundational in the development of vaccines, which often include weakened or inactivated forms of antigens to prepare the immune system for future encounters with the actual pathogen.