Which immunoglobulin is associated with hypersensitivity reactions such as asthma?

• A. IgA
• B. IgD
• C. IgE
• D. IgG

Answer: (C)

IgE is the antibody most closely linked to allergic hypersensitivity reactions like asthma. In susceptible individuals, an allergen triggers a Th2 response that promotes class switching to IgE; the produced IgE binds to high-affinity receptors on mast cells and basophils, effectively arming them for later responses. Upon re-exposure, the allergen cross-links the bound IgE, causing rapid degranulation and release of histamine, leukotrienes, and other mediators. These substances lead to bronchoconstriction, airway inflammation, and increased mucus production, all hallmarks of asthma. Other immunoglobulins have different roles—IgA primarily protects mucosal surfaces, IgD mainly serves as a B cell receptor, and IgG is involved in opsonization and neutralization—so IgE is the one most associated with this type of hypersensitivity.