What is an antigen?

An antigen is a substance that triggers an immune response in the body. It is typically a molecule, often a protein or polysaccharide, that is recognized by the immune system as foreign or harmful, prompting the body to mount a defense against it. Antigens can be found on the surface of pathogens such as bacteria and viruses, but they can also be components of pollen, dust, or even food, making them central to allergic reactions in some individuals.

When an antigen enters the body, it is identified by specific immune cells, which then initiate a cascade of immune responses involving the activation of various cells, including T cells and the production of antibodies by B cells. This process is crucial for the development of immunity and helps the body protect itself from infections and diseases.

Understanding what an antigen is highlights its role in immunology and the body’s defense mechanisms, which is a fundamental concept in biomedical studies.