Which mediator is primarily responsible for pruritic lesions in an IgE-mediated hypersensitivity reaction?

In an IgE-mediated hypersensitivity reaction, histamine plays a crucial role in the development of pruritic lesions, or itchy skin conditions. When an allergen is encountered by the immune system in a sensitized individual, it triggers the activation of B cells that produce IgE antibodies. These antibodies bind to mast cells and basophils, leading to their degranulation upon subsequent exposure to the same allergen.

The degranulation of these cells releases several mediators, with histamine being one of the most significant. Histamine acts primarily on the H1 receptors in the skin and other tissues, causing vasodilation and increased vascular permeability. This results in edema, redness, and the characteristic itch associated with allergic reactions. The release of histamine directly correlates with the pruritus experienced during these hypersensitivity responses, making it the primary mediator responsible for the symptoms.

Other mediators, such as cytokines, neutrophils, and macrophages, also play roles in the immune response; however, they are more involved in the broader inflammatory response and do not directly cause the itching sensation associated with pruritic lesions in this type of hypersensitivity.