Acquired immune system

The adaptive immune system, also known as the acquired immune system or, more rarely, as the specific immune system, is a subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system). The adaptive immune system, also known as the acquired immune system or, more rarely, as the specific immune system, is a subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system). Acquired immunity creates immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to subsequent encounters with that pathogen. This process of acquired immunity is the basis of vaccination. Like the innate system, the acquired system includes both humoral immunity components and cell-mediated immunity components. The term 'adaptive' was first used by Robert Good in reference to antibody responses in frogs as a synonym for 'acquired immune response' in 1964. Good acknowledged he used the terms as synonyms but explained only that he 'preferred' to use the term 'adaptive'. He might have been thinking of the then not implausible theory of antibody formation in which antibodies were plastic and could adapt themselves to the molecular shape of antigens, and/or to the concept of 'adaptive enzymes' as described by Monod in bacteria, that is, enzymes whose expression could be induced by their substrates. The phrase was used almost exclusively by Good and his students and a few other immunologists working with marginal organisms until the 1990s when it became widely used in tandem with the term 'innate immunity' which became a popular subject after the discovery of the Toll receptor system in Drosophila, a previously marginal organism for the study of immunology. The term 'adaptive' as used in immunology is problematic as acquired immune responses can be both adaptive and maladaptive in the physiological sense. Indeed, both acquired and innate immune responses can be both adaptive and maladaptive in the evolutionary sense. Most textbooks today, following the early use by Janeway, use 'adaptive' almost exclusively and noting in glossaries that the term is synonymous with 'acquired'.