IgE is required for antibody-dependent cellular cytotoxicity of eosinophils in response to helminthic infections.
Eosinophils contribute to host defense against parasitic infection through antibody-dependent cellular cytotoxicity (ADCC). The process of eosinophil-mediated ADCC begins when free IgE binds to parasites in the blood stream. Subsequently, eosinophils recognize and bind the Fc region of bound IgE through a high-affinity Ig-E specific Fc receptor called FcaRI. Finally, eosinophils kill the parasite by releasing cytoplasmic granules that contain cytotoxic proteins such as major basic protein (MBP), eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin. In addition to aiding in host defense against parasites, eosinophils also regulate type I hypersensitivity reactions.
Illustration A is an eosinophil in a peripheral blood smear. Eosinophils have cytoplasmic granules that have a high affinity for the bright, orange-red eosin stain. They often display a bilobed nucleus.
Answers 1 & 3-5: IgA, IgM, IgG, and IgD are not significantly involved in the ADCC response to helminthic infections. IgG is, however, involved in the ADCC response to infected cells mediated by Natural Killer (NK) cells.