acquired immunity, any form of immunity that is not innate and is obtained during life as a result of the development of antibodies in response to an antigen. It may be naturally or artificially acquired and actively or passively induced. Naturally acquired immunity is obtained by the development of antibodies resulting from an attack of infectious disease or by the transmission of antibodies from the mother through the placenta to the fetus or to the infant through colostrum and breast milk. Artificially acquired immunity is obtained by vaccination or by the injection of immune gamma globulin. Acquired immunity can be divided into cell-mediated immunity (T cells) and humoral immunity (B cells). Compare natural immunity. See also active immunity, passive immunity.
