What is the primary mediator released from mast cells during a Type 1 hypersensitivity reaction?

Histamine is the primary mediator released from mast cells during a Type 1 hypersensitivity reaction. When an individual is exposed to an allergen for the first time, their immune system produces Immunoglobulin E (IgE) antibodies specific to that allergen. These IgE antibodies then bind to mast cells and basophils, sensitizing them to future exposures to the allergen.

Upon subsequent exposure to the same allergen, cross-linking of the IgE on the surface of mast cells occurs. This triggers the mast cells to degranulate, leading to the release of several mediators, with histamine being one of the most significant. Histamine causes various effects, including vasodilation, increased vascular permeability, and smooth muscle contraction, which often result in the symptoms associated with allergic reactions such as itching, swelling, and bronchoconstriction.

While cytokines and prostaglandins play a role in the inflammatory response and can contribute to the symptoms of a Type 1 hypersensitivity reaction, they are not the primary mediators released upon the initial triggering of mast cells. Instead, histamine acts quickly and is responsible for the immediate symptoms experienced during an allergic response. IgE, although critical in the sensitization process and key to