Answer:
Antigens are substances that activate the adaptive immune response.
Explanation:
An antigen is a molecule or a substance that activates or stimulates immune response most especially the adaptive immune system made up of lymphocytes e.g B cells and T cells. The stimulation of lymphocytes leads to the production of antibodies.
Antigens could either be hetero-antigen (foreign) or auto-antigen (self). Hetero-antigens could be substances produced by microorganisms or certain foods, while auto-antigens are produced in the body. Although the body recognizes auto-antigens, but in autoimmune disorders the body doesn't recognize auto-antigens.
