What is the Origin of Hypersensitivity Reaction?

The term is a precise medical description of an over-reactive biological process. "Hypersensitivity" combines the Greek hyper, meaning over or excessive, with "sensitivity," referring to the body's level of responsiveness to a stimulus. "Reaction" refers to the resulting physiological response to the antigen. The term was formally introduced in the early 20th century to categorize these detrimental, immune-mediated responses that cause damage to the host's own tissues.

What is the Mechanism of Hypersensitivity Reaction?

Hypersensitivity reactions involve a complex, dysregulated cascade of immune cells and potent signaling molecules. For instance, Type I reactions are initiated by the initial sensitization phase where plasma B cells produce IgE antibodies specific to the antigen. Upon subsequent re-exposure, the antigen cross-links IgE fixed on the surface of mast cells and basophils, triggering the rapid release of powerful inflammatory mediators like histamine and leukotrienes. This rapid degranulation leads to the immediate physiological effects, such as vasodilation and smooth muscle contraction, demonstrating a failure in immune tolerance.

Hypersensitivity Reaction

Meaning

A Hypersensitivity Reaction is an exaggerated or inappropriate immune response to an antigen that is normally considered harmless, resulting in significant tissue damage and systemic physiological dysfunction. These detrimental reactions are clinically categorized into four main types, Type I through Type IV, based on the specific immunological mechanism and the speed of the onset. In clinical practice, the careful management of these reactions is paramount as they can range from uncomfortable allergic symptoms to acute, life-threatening anaphylaxis.