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.
Kucik et al. review common intestinal parasites found in the United States, which include Enterobius vermicularis, Giardia lamblia, Ancylostoma duodenale, Necator americanus, and Entamoeba histolytica. They report that eosinophilia occurs in 30-60% of N. americanus infection, which is the second most common helminthic infection in the United States.
Walsh et al. studied the effect of the humoral immune response on the parasitic worm, N. americanus. Both upon infection and two years after, the group demonstrated that high IgE levels and high eosinophil counts correlated negatively with parasite weight and fecundity.
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 1,3,4&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.
Kucik CJ, Martin GL, Sortor BV. Common Intestinal Parasites. Am Fam Physician. 2004 Mar 1;69(5):1161-1169.
PMID:15023017 (Link to Abstract)
Pritchard DI, Quinnell RJ, Walsh EA. Immunity in humans to Necator americanus: IgE, parasite weight and fecundity. Parasite Immunol. 1995 Feb;17(2):71-5.
PMID:7761110 (Link to Abstract)