Which immunoglobulin is most closely associated with eosinophil activation in parasitic infections?

• A. IgA
• B. IgM
• C. IgG
• D. IgE

Answer: (D)

Eosinophils are the key effector cells against helminthic parasites, and their activation is driven most strongly by IgE antibodies. In a parasitic infection, a Th2 response leads to production of parasite-specific IgE, which coats the surface of the parasite. Eosinophils have high-affinity Fc receptors for IgE (FcεRI); when IgE bound to the parasite cross-links upon encountering the same antigen again, the eosinophils are activated and release cytotoxic granule proteins such as major basic protein and eosinophil-derived cationic proteins. This degranulation damages or kills the parasite. IL-5 further enhances eosinophil numbers and responsiveness, boosting this effect. While other antibodies like IgG can mediate opsonization and ADCC by different effector cells, IgE specifically orchestrates eosinophil-driven antiparasitic activity, making it the best fit for this scenario.