Elevated IgE levels are typically found in

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

Answer: (A)

Elevated IgE levels point to immediate, IgE-mediated allergic reactions. In these responses, allergens promote a Th2-skewed response that drives B cells to switch to producing IgE, often aided by IL-4. The IgE then binds to high-affinity receptors on mast cells and basophils, sensitizing them. When the same allergen is encountered again, cross-linking of the bound IgE triggers rapid degranulation and release of histamine, leukotrienes, and other mediators, leading to the symptoms of allergy. This pattern is typical in atopy and conditions like allergic rhinitis, asthma, and certain food allergies. Other hypersensitivity types involve different antibodies or mechanisms (Type II mainly IgG/IgM against cells, Type III immune complexes, Type IV T-cell–mediated), and do not rely on IgE elevation.