Antigen

An antigen is any substance that triggers an immune response in the body. This response involves the production of antibodies that specifically target and neutralize the antigen. Antigens can be proteins, polysaccharides, lipids, or nucleic acids, and they are typically found on the surface of pathogens like bacteria, viruses, fungi, and parasites. They can also originate from non-infectious sources such as food, pollen, or transplanted organs. The immune system recognizes these foreign molecules as threats, initiating a cascade of events to eliminate them. This recognition is facilitated by antigen-presenting cells and T cell receptors, which allow for the adaptive immune response to identify and remember antigens for future encounters. The response involves antibody production, cell-mediated immunity, and immune memory to protect the host.

Antigen meaning with examples

• During a bacterial infection, bacterial cell wall components act as antigens. These antigens trigger the immune system to produce antibodies specific to those bacterial markers. These antibodies bind to the bacteria, flagging them for destruction by other immune cells, preventing the spread of the infection. In essence, the bacteria's surface antigens are the key that unlocks the immune response's power.
• Vaccines work by introducing weakened or inactive forms of antigens to the body. These antigens, such as those derived from viruses, stimulate the immune system to produce antibodies and memory cells. If the individual encounters the real virus in the future, their immune system can swiftly recognize and neutralize it. This results in the prevention of the disease or a milder form of it.
• In allergic reactions, certain substances like pollen or food proteins can act as antigens. When these antigens enter the body of a sensitized individual, the immune system overreacts. This leads to the release of histamine and other inflammatory chemicals, causing symptoms such as sneezing, itching, or even anaphylaxis in severe cases.
• When a foreign organ is transplanted, the donor's antigens can be recognized as foreign by the recipient's immune system. The immune system then launches an attack against the transplanted organ, leading to rejection. Immunosuppressant drugs are often used to suppress this immune response and prevent organ rejection, allowing the new organ to function.