reaginic

Reaginic is a historical immunology term describing serum antibodies associated with immediate hypersensitivity reactions. The word derives from reagin, the serum factor once thought to mediate allergic responses in early 20th-century serology. Reaginic antibodies were described as circulating factors capable of triggering mast cell or basophil degranulation when exposed to allergens, producing the rapid, IgE-mediated symptoms characteristic of type I hypersensitivity.

In modern immunology, these reaginic antibodies are understood largely as immunoglobulin E (IgE) antibodies in humans. IgE binds to allergens and sensitize mast cells and basophils, leading to mediator release and allergic manifestations such as rhinitis, asthma, or anaphylaxis. Because this framework aligns with the IgE model, the term “reaginic” is now largely historical and rarely used in contemporary practice.

Today, allergy diagnostics rely on IgE-based approaches, including skin-prick testing and serum specific IgE assays, rather than the older reaginic terminology. The concept of reaginic reactions contributed to the foundational understanding of immediate-type hypersensitivity and the development of serologic tests in the early history of allergy and immunology.

See also: Immunoglobulin E, Type I hypersensitivity, Allergy.