Antigen

An antigen is a molecule or a structure found on the surface of a cell or a virus that can be recognized by the immune system. Antigens can be proteins, carbohydrates, lipids, or other molecules. When an antigen is recognized by the immune system, it triggers an immune response which leads to the production of antibodies or the activation of other immune cells. Antigens can be either self (produced by the body) or non-self (produced by an outside source, such as a virus or bacteria). The immune system uses antigens to detect foreign substances, such as bacteria, viruses, and toxins, and to differentiate between self and non-self. This process is called antigen recognition and is mediated by antigen-presenting cells (APCs). APCs display antigens on their surface which are recognized by the immune system and activate a specific immune response. Antigens can also be used to create vaccines which help to protect against disease. Vaccines contain antigens which are injected into the body. This stimulates the immune system to produce antibodies which are specific to the antigen and can recognize it if it enters the body again. In addition, antigens can be used in laboratory settings to identify specific molecules or structures. For example, antibodies tagged with fluorescent dyes can be used to detect antigens on cells or viruses, allowing scientists to study their structure and function.