Which antibody is responsible for causing anaphylactic reactions?

• A. IgE
• B. IgG
• C. IgM
• D. IgA

Answer: (A)

Anaphylactic reactions are driven by IgE antibodies. In sensitized individuals, these IgE molecules bind to mast cells and basophils via FcεRI receptors. When the allergen is encountered again, it cross-links the bound IgE, triggering rapid degranulation of these cells and release of mediators like histamine, leukotrienes, and prostaglandins. This mediator surge causes widespread vasodilation, increased vascular permeability, bronchoconstriction, and swelling—producing the life-threatening symptoms of anaphylaxis. Other antibodies (IgG, IgM, IgA) aren’t the primary mediators of this immediate, severe allergic reaction. Clinically, recognizing IgE-mediated type I hypersensitivity helps explain why epinephrine is the first-line treatment.