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Adaptive Immunity Definition. Adaptive immunity is an important part of the immune system. It is protection from an infectious disease agent that is mediated by B-and T-lymphocytes following exposure to specific antigen, and characterized by immunological memory.
Medical Definition of ACTIVE IMMUNITY. : usually long-lasting immunity that is acquired through production of antibodies within the organism in response to the presence of antigensâcompare acquired immunity, innate immunity, passive immunity. usu. long-lasting immunity that is acquired through production of antibodies within the organism in response to the presence of antigens â compare passive immunity. See active immunity defined for kids. ADVERTISEMENT.