Which immunoglobulin class is most commonly associated with allergic reactions?

• A. IgG
• B. IgM
• C. IgA
• D. IgE

Answer: (D)

Allergic reactions are driven by immunoglobulin E (IgE). In atopic individuals, IgE specific to an allergen binds to high‑affinity receptors on mast cells and basophils. When the same allergen appears again, it cross‑links the IgE on these cells, triggering degranulation and release of histamine and other mediators. This rapid mediator release causes the classic symptoms of immediate hypersensitivity: itching, swelling, mucus production, and bronchoconstriction.

Other antibody classes have different roles in immunity: IgG is key for blocking and opsonizing pathogens during later or systemic responses; IgM is the first antibody produced in a primary response and helps activate complement; IgA protects mucosal surfaces. None of these are the primary drivers of the typical allergic reaction, which is why IgE is the class most commonly associated with allergies.