APA Dictionary of Psychology

n. the ability of the body to resist infection, based on the actions of the immune system in mounting immune responses. Active immunity arises when immune cells (see lymphocyte) produce, and remain able to produce, appropriate antibodies following infection or deliberate stimulation (immunization). Passive immunity is conferred by the introduction of antibodies from another organism (e.g., via colostrum). Innate immunity does not require prior contact with invading microorganisms or tissues and involves nonspecific immune responses. See also antigen–antibody reaction.