Evidence for IgE-dependent cytotoxicity by rat eosinophils

Human and rodent eosinophils have been shown previously to act as effector cells against Schistosoma mansoni schistosomula by ADCC mechanisms involving IgG antibodies. The present work brings novel evidence for the existence in rat schistosomiasis of an IgE-eosinophil dependent cytotoxicity mechanism. The role of IgE antibodies present in the rat serum after 6 weeks of infection was clearly established by immunoadsorption and inhibition experiments, whereas the participation of IgG and complement in this system could be ruled out. Mast cell products, including ECF-A tetrapeptides, appear to play an essential role in significantly increasing eosinophil cytotoxicity. A kinetic study of the IgG-dependent cytotoxicity mechanism previously described and of this IgE-mediated mechanism according to rat schistosomiasis revealed the preeminent role played by IgG antibodies in early infection, whereas IgE predominated after 6 wk of infection. The possible significance of IgE-eosinophil cooperation in ADCC mechanisms in parasite and nonparasite models is discussed.