Although eosinophilia is a hallmark ofhelminth infections, the function ofthe eosinophil granulocyte remains unknown. The recent development of a monospecific rabbit antimouse antieosinophil serum (AES)' in our laboratories (1) has provided a unique tool by which the roles of eosinophils may be elucidated . Using a murine model of schistosomiasis, the most important helminth infection of man (2), the kinetics of eosinophilia in the peripheral blood, bone marrow, and tissue lesions was carefully established; this was followed by an examination of the effects of AES on these reactions.In previous studies of the eosinophilia in schistosomiasis in mice the animals were hyperinfected, and mortality was high in the acute stages of infection (3, 4) . Mice exposed to relatively low numbers of cercariae, however, will survive for at least a year despite the development of mild to moderate hepatosplenic disease (5, 6) . The kinetics of eosinophilia in the peripheral blood and bone marrow was studied, therefore, in mice exposed to three different intensities of infection and the responses were followed for as long as 20 wk.The effect of Schistosoma mansoni eggs on eosinophilia in the blood, bone marrow and granulomatous lesions was then examined by injecting isolated purified eggs into mice singly and multiply by various routes . While the host response was dependent on the route of injection, primary and anamnestic secondary reactions were seen after successive intravenous injections. Administration of AES under these conditions profoundly suppressed peripheral eosinophilia, induced a marked increase in eosinophil precursors in the bone marrow, and ablated eosinophils from the tissue lesions, considerably reducing their size .
Materials and MethodsAnimals . Young adult female mice of the CF-1 strain (18-22 g in body weight) obtained from Carworth Farms, Inc. were used in these experiments .Eosinophilia in Naturally Infected Mice . Groups of mice were infected by the subcutaneous injection of 10, 50, or 200 cercariae of the Puerto Rican strain of S . mansoni as described by Peters and Warren (7). The worm burden in each of the experimental groups was assessed by perfusion of 10 mice 8 wk after infection (8). Eosinophil counts on five animals in each group were done weekly for the first 6 wk after infection and then at 2-wk intervals.