In type I hypersensitivity, which cell type is primarily responsible for releasing mediators that cause symptoms?

In type I hypersensitivity, which cell type is primarily responsible for releasing mediators that cause symptoms?

• A. T cells
• B. Mast cells
• C. B cells
• D. Neutrophils

Answer: (B)

Mast cells are the primary source of the immediate mediators in type I hypersensitivity. When an allergen binds to IgE that has attached to FcεRI receptors on the surface of mast cells (and to a lesser extent basophils), the cross-linking triggers degranulation. This releases histamine and other preformed mediators stored in granules, plus newly synthesized leukotrienes and prostaglandins. These mediators cause the hallmark symptoms: increased vascular permeability leading to swelling, vasodilation, mucus production, itching, and, in the airways, bronchoconstriction. While B cells generate the IgE that arms the response and T helper cells (especially TH2) help drive IgE production, the actual release of the symptomatic mediators is carried out by mast cells.

Mast cells are the primary source of the immediate mediators in type I hypersensitivity. When an allergen binds to IgE that has attached to FcεRI receptors on the surface of mast cells (and to a lesser extent basophils), the cross-linking triggers degranulation. This releases histamine and other preformed mediators stored in granules, plus newly synthesized leukotrienes and prostaglandins. These mediators cause the hallmark symptoms: increased vascular permeability leading to swelling, vasodilation, mucus production, itching, and, in the airways, bronchoconstriction. While B cells generate the IgE that arms the response and T helper cells (especially TH2) help drive IgE production, the actual release of the symptomatic mediators is carried out by mast cells.