In vitro incubation of the various stages of the nematode parasite Trichinella spiralis was performed with murine eosinophils, neutrophils, or mononuclear cells in the presence or absence of immune mouse serum. It was found that eosinophils, in the presence of immune but not normal mouse serum, destroyed the newborn larval stage of the parasite in vitro. Neutrophils were significantly less cytotoxic, and mononuclear cells did not kill in this in vitro assay. The eosinophil effect on the newborn larvae was confirmed by their decreased infectivity on injection into mice. Eosinophil-mediated parasite destruction was dependent on a 7S antibody that appeared by 3 weeks after T. spiralis infection and which was specific for the newborn larval stage of the parasite. Detailed electron microscopic examination of the cell-parasite interaction showed that during the initial 4 hr of incubation, eosinophils were closely applied to the surface of the helminth and spread long pseudo-pods over its cuticle. By 8 hr, electron dense deposits appeared on the surface of the newborn larvae concomitant with a decrease in the number of crystalloid granules visible within the attached eosinophils. Irregularities in the parasite cuticle were evident at this time. By 10 hr of incubation, fractures in the cuticle and disintegration of the parasite internal structures were visualized. In vitro models of host resistance to multicellular parasites, such as this one, in which morphologic destruction of the target organism can be directly visualized, quantitated, and characterized should provide a useful tool for elucidation of the basic mechanism of the eosinophil’s protective role.
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Kazura et al. (1980) studied this question.