Which immunoglobulin class is most commonly associated with allergic reactions such as asthma?

• A. IgA
• B. IgD
• C. IgE
• D. IgG

Answer: (C)

Allergic reactions like asthma are driven by IgE-mediated immediate hypersensitivity. IgE binds to allergens and anchors on high-affinity receptors on mast cells and basophils. When the same allergen is encountered again, the IgE molecules cross-link, triggering these cells to release histamine, leukotrienes, and other mediators that cause bronchoconstriction, increased mucus, and airway inflammation typical of asthma. In allergic individuals, Th2-type responses promote B cells switching to IgE production in response to the allergen. Other immunoglobulins have different roles: IgA protects mucosal surfaces but isn’t the main driver of allergic asthma; IgD mainly acts as a B cell receptor with limited circulating effector role; IgG is the most abundant circulating antibody involved in opsonization and secondary responses, not the immediate hypersensitivity reaction that underlies asthma.