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Hypersensitivity reactions
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Hypersensitivity reactions are the immune system overreacting: the body's defenses go too far. The Gell and Coombs classification sorts them into four types, based on which part of the immune system is involved.
In type I, IgE, a type of antibody, is in charge. IgE prompts cells called mast cells and basophils to release histamine, and that is what happens in allergic rhinitis. In type II, other antibodies are involved, IgG or IgM, which bind to the body's own cells and lead to their destruction, as happens in autoimmune hemolytic anemia.
In type III, antibodies and antigens, the molecules that antibodies recognize, clump together into small aggregates called complexes. These complexes settle in tissues the way scale settles at the bottom of a kettle, and that happens in lupus. Type IV is different: it relies not on antibodies but on T lymphocytes, a type of white blood cell, and it takes time to appear, like the dermatitis that poison ivy leaves behind.
In brief
Hypersensitivity reactions are exaggerated immune responses; the Gell and Coombs classification distinguishes four types.
In type I, IgE causes mast cells and basophils to release histamine, as in allergic rhinitis; in type II, IgG or IgM binds to the body's own cells and leads to their destruction, as in autoimmune hemolytic anemia.
In type III, antigen-antibody complexes deposit in tissues, as in lupus; type IV relies on T lymphocytes, not antibodies, and is delayed, as in poison ivy dermatitis.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingType I Hypersensitivity Reaction, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated