IgE-mediated and mast cell degranulation describe which type of hypersensitivity?

• A. Type II hypersensitivity
• B. Type I hypersensitivity
• C. Type III hypersensitivity
• D. Type IV hypersensitivity

Answer: (B)

IgE-mediated and mast cell degranulation describe immediate-type hypersensitivity, also known as Type I. In this reaction, exposure to an allergen leads B cells to produce IgE, which binds to FcεRI receptors on mast cells and basophils. When the allergen cross-links these IgE molecules, it triggers rapid degranulation and release of histamine, leukotrienes, and prostaglandins. This causes the hallmark immediate symptoms: vasodilation, increased vascular permeability, smooth muscle constriction (including bronchoconstriction), and mucus production. A later phase can involve eosinophils and cytokines contributing to ongoing inflammation. This differs from the other hypersensitivity types: Type II is antibody-mediated cytotoxicity against cell surface antigens, Type III involves immune complex deposition, and Type IV is driven by T cells in a delayed fashion.