1. Immunity induced in the host itself by antigen and lasts much longer, sometimes lifelong. (wikipedia.org)
2. A form of acquired immunity in which the body produces its own antibodies against disease-causing antigens. (wordnetweb.princeton.edu)
3. The immunity that results from the production of antibodies by the immune system in response to the presence of an antigen. (Google Dictionary)
4. A type of immunity or resistance developed in an organism by its own production of antibodies in response to an exposure to an antigen, a pathogen or to a vaccine. (biology-online.org)