(type i hypersensitivity) An inflammatory response driven by antigen recognition by antibodies bound to Fc receptors on mast cells or basophils, occurring within minutes after exposure of a sensitized individual to the antigen, and leading to the release of a variety of inflammatory mediators such as histamines.

(type i hypersensitivity) Immediate hypersensitivity reaction - type I reaction, involves immunoglobulin E (IgE)-mediated release of chemical mediators from mast cells and basophils. Th2 cells produce IL-4 and IL-13, which then act on B cells to promote the production of antigen-specific IgE. Reexposure to the antigen can then result in the antigen binding to and cross-linking the bound IgE antibodies on the mast cells and basophils. This causes the release of preformed mediators (histamine, tryptase, tryptase, chemotactic factors), newly synthesized mediators (leukotrienes, prostaglandin, thromboxane, platelet-activating factor, adenosine, bradykinin), and cytokines from these cells that results in structural and functional changes to the affected tissue.

A category of allergic reaction, triggered by specific allergens and involving IgE. The majority of allergic reactions to pollens, pets, dust, mold, food, and insect venom are of this type.

Hypersensitivity reactions which occur within minutes of exposure to challenging antigen due to the release of histamine which follows the antigen-antibody reaction and causes smooth muscle contraction and increased vascular permeability.

(type i immediate hypersensitivity reaction) An immunoglobulin E (IgE) mediated hypersensitivity reaction. These usually occur within an hour of exposure to an allergen.