Which antibody mediates immunity to parasitic worms?

• A. IgG
• B. IgA
• C. IgE
• D. IgM

Answer: (C)

IgE is the antibody specialized for defense against large extracellular parasites like helminths. When parasite antigens are bound by IgE, the Fc region engages Fc receptors on eosinophils, as well as on mast cells and basophils. This sets up eosinophil-mediated cytotoxicity: eosinophils attach to IgE-coated parasites and release granule proteins such as major basic protein that damage the worm’s surface. At the same time, mast cell and basophil degranulation releases mediators that increase mucus production, smooth muscle contraction, and vascular permeability, helping to expel the parasite. The Th2 response drives IgE production and eosinophil activation, reinforcing this defense. Other antibodies like IgG, IgM, or IgA have their roles (IgG in opsonization, IgM in early responses, IgA at mucosal surfaces), but they’re not as specialized for targeting large helminths as IgE is.