Anaphylaxis is an acute, potentially lethal, multisystem syndrome resulting from the sudden release of mast cell- and basophil-derived mediators into the circulation . It most often results from immunologic reactions to foods, medications, and insect stings, although it can also be induced through nonimmunologic mechanisms by any agent capable of producing a sudden, systemic degranulation of mast cells or basophils .
The phenomenon of anaphylaxis was first described in the modern medical literature in 1902 in a study involving protocols for immunizing dogs with jellyfish toxin. The injection of small amounts of toxin in some animals, rather than generating protection, precipitated the rapid onset of fatal or near-fatal symptoms . The authors named this response "l'anaphylaxie," which is derived from the Greek words a- (against) and phylaxis (immunity or protection).
The pathophysiology of anaphylaxis will be reviewed here. The clinical manifestations, diagnosis and management of anaphylaxis, and the epidemiology and etiology of fatal anaphylaxis are discussed separately. (See "Anaphylaxis: Rapid recognition and treatment" and "Fatal anaphylaxis".)
PROPOSED IMMUNOPATHOLOGIC MECHANISMS
The mechanism responsible for most cases of human anaphylaxis involves immunoglobulin E. Possible alternative mechanisms remain incompletely understood. Environmental exposures and complex genetic factors may also have important roles, although these are not explored in this review.
Terminology — The term anaphylaxis has traditionally been reserved for IgE-dependent events, and the term "anaphylactoid reaction" has been used to describe IgE-independent events, although the two reactions are often clinically indistinguishable. The World Allergy Organization (WAO), an international umbrella organization representing a large number of regional and national professional societies dedicated to allergy and clinical immunology, has proposed discarding this nomenclature. The WAO categorizes anaphylaxis as either immunologic or nonimmunologic, and this is the terminology used in this review .