acquired immunity

resistance resulting from previous exposure of the individual in question to an infectious agent or antigen; it may be active and specific, as a result of naturally acquired (apparent or inapparent) infection or intentional vaccination (artificial active immunity); or it may be passive, being acquired from transfer of antibodies from another person or from an animal, either naturally, as from mother to fetus, or by intentional inoculation (artificial passive immunity), and, with respect to the particular antibodies transferred, it is specific. Passive, cell-mediated immunity produced by the transfer of living lymphoid cells from an immune (allergic or sensitive) animal to a normal one is sometimes referred to as adoptive immunity.