Introduction to Antigen


An antigen is a substance that can trigger an immune response in the body. The immune system is a complex network of cells and molecules that protects us from harmful invaders, such as bacteria, viruses, parasites, and toxins. The immune system recognizes these invaders as foreign and tries to eliminate them.

The immune system can distinguish between self and non-self molecules by using special receptors on its cells. These receptors can bind to specific parts of the foreign molecules, called antigens. An antigen is any molecule that can be recognized by an immune receptor and elicit an immune response.

An antigen can induce the formation of two types of immune products: antibodies and T cells. Antibodies are proteins that circulate in the blood and bind to antigens with high specificity and affinity. T cells are white blood cells that can directly kill infected cells or help other immune cells to produce antibodies or cytokines (chemical messengers).

Not all antigens are immunogens, meaning that they can activate the immune system and induce an immune response. Some antigens are too small or too similar to self molecules to be recognized by the immune system. Some antigens may require additional signals or helper molecules to be immunogenic.

The term antigen is derived from the words antibody generator, indicating its role in stimulating antibody production. However, antigens can also stimulate T cell responses, which are essential for cellular immunity and immunological memory.

Antigens can originate from outside or inside the body. Foreign antigens are those that come from external sources, such as microbes, toxins, pollen, or transplanted organs. Self antigens are those that are normally present in the body, such as proteins, nucleic acids, or lipids. Self antigens usually do not trigger an immune response, unless they are altered or presented in an abnormal way. This can lead to autoimmune diseases, where the immune system attacks its own tissues.

Antigens play a key role in the adaptive immunity, which is the branch of the immune system that can learn from previous exposures and generate specific and long-lasting responses against specific antigens. Antigens are also involved in the innate immunity, which is the first line of defense against pathogens and does not require prior exposure or memory.

Antigens are diverse and complex molecules that can vary in their size, shape, structure, and function. Antigens can be classified into different types based on their origin, chemical nature, immunogenicity, and antigenicity.