What is the mechanism underlying Type 1 hypersensitivity?

Type 1 hypersensitivity, also known as immediate hypersensitivity, is primarily characterized by an IgE-mediated response. The mechanism involves the sensitization phase, where an allergen triggers the production of specific IgE antibodies by plasma cells. These IgE antibodies bind to high-affinity IgE receptors on the surface of mast cells and basophils.

Upon subsequent exposure to the same allergen, the cross-linking of the IgE antibodies bound to these cells leads to degranulation. During this process, mast cells release various mediators such as histamine, leukotrienes, and prostaglandins, which contribute to the acute inflammatory response. This cascade of events results in the classic symptoms associated with allergic reactions, such as bronchoconstriction, vasodilation, increased vascular permeability, and mucus secretion.

The unique aspect of Type 1 hypersensitivity is its rapid onset, often occurring within minutes of allergen exposure due to the pre-formed IgE and the quick release of mediators from mast cells. Understanding this specific mechanism highlights why degranulation of IgE-sensitized mast cells is central to the pathophysiology of Type 1 hypersensitivity reactions.