After earlier observations that antibody-dependent, cell-mediated damage to 51Cr-labeled schistosomula can be ablated by pretreatment of a mixed preparation of human peripheral blood leukocytes with an anti-eosinophil serum and complement, we investigated the cytotoxic effects of eosinophil-enriched cell preparations. Preparations containing up to 98.5% eosinophils and devoid of neutrophils were effective in mediating antibody-dependent damage to schistosomula. Preparations enriched in mononuclear cells or in neutrophils, and devoid of eosinophils, were inactive. Eosinophils from some patients with eosinophilia induced by schistosomiasis were less active on a cell-to-cell basis than cells from normal individuals. The possibility that such cells were initially blocked by immune complexes was considered, and it was found that reasonable cytotoxicity by purified eosinophils from patients with eosinophilia could be generated by overnight cultures. A possible requirement for cooperation between eosinophils and other cell types was also studied. Lymphocytes, neutrophils and monocytes failed to enhance eosinophil-mediated cytotoxicity. These results provide further evidence that the eosinophil is the only cell in man responsible for antibody-dependent, complement-independent damage to schistosomula in vitro. Eosinophils from individuals, however, differ in their cytotoxic potential by a mechanism yet to be elucidated. The possible relationship of these findings to immunity in vivo is discussed.

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Summary.-We measured the effect of 6 standard (Adriamycin, BCNU, DTIC, melphalan, vinblastine, actinomycin D) These investigations furnish a quantitative description of the chemosensitivity of human metastatic melanoma CFU. Additionally, these studies serve as a useful step towards the development of an in vitro chemosensitivity test for human melanoma, and provide an operational quantitative basis for further exploration of in vitrodirected therapy in metastatic neoplasms.

SUMMARYThe cell-mediated resistance of human leucocytes toTrypanosoma dionisii, a bat parasite related toT. cruzi, was investigated. Human peripheral blood neutrophils and monocytes were cytotoxic toT. dionisiias assessed by electron microscopy and by induction of99mTc release from trypanosomes pre-labelled with [99mTc]pertechnetate. The enhancement of cytotoxicity by specific antiserum varied considerably from one individual to another. Neither blood lymphocytes nor blood eosinophils induced99mTc release fromT. dionisii. The trypanosomes were readily phagocytosed by neutrophils and monocytes even in the absence of added antiserum but the rate was enhanced when antiserum was present. Eosinophils also phagocytosedT. dionisiibut only in the presence of antiserum. Investigation by electron microscopy revealed thatT. dionisiiis rapidly destroyed in the phagocytic vacuole of neutrophils and monocytes and by eosinophils. Phagocytosis, ultrastructural damage and induction of99mTc release occurred more rapidly in neutrophils than in monocytes.

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