Which class of antibodies is primarily involved in allergic reactions?

• A. IgA
• B. IgM
• C. IgE
• D. IgD

Answer: (C)

Allergic reactions are driven by immunoglobulin E. When an allergen is encountered, helper T cells skew toward a Th2 response and promote B cells to switch to producing IgE. This IgE binds with high affinity to FcεRI receptors on mast cells and basophils, sensitizing them. Upon subsequent exposure, the allergen cross-links the IgE on these cells, triggering degranulation and the release of histamine, leukotrienes, and other mediators. Those substances cause the classic allergy symptoms: itching, swelling, mucus production, bronchoconstriction, and vasodilation.

IgA mainly protects mucosal surfaces and isn’t the key player in immediate allergic reactions. IgM is the first antibody produced in responses and activates complement, but it doesn’t mediate the rapid, IgE-driven hypersensitivity seen in allergies. IgD mostly serves as a B cell receptor and is not a major mediator of allergic effector functions.

So the antibody class most involved in allergic reactions is IgE.