Which antibody is primarily involved in allergic reactions and defense against parasites?

• A. IgE
• B. IgA
• C. IgG
• D. IgM

Answer: (A)

IgE is the antibody type most closely tied to allergic reactions and defense against parasites. In allergies, IgE binds to high-affinity receptors on mast cells and basophils. When an allergen cross-links these bound IgE molecules, these cells release histamine and other mediators, producing the symptoms of an allergic response. For parasites, especially helminths, IgE-coated parasites are targeted by eosinophils; eosinophils bind the IgE via Fc receptors and release toxic granules to help kill the parasite. Other immunoglobulins have different primary roles—IgA protects mucosal surfaces, IgG handles neutralization, opsonization, and complement activation, and IgM is the first responder in primary responses and also activates complement.