Antibody-Dependent Eosinophil-Mediated Damage to 51Cr-Labeled Schistosomula of Schistosoma Mansoni: Mediation by IgG, and Inhibition by Antigen-Antibody Complexes
The properties of the antibodies responsible for complement-independent, eosinophil-mediated damage to schistosomula have been characterized in serum samples from Schistosoma mansoni-infected baboons and human patients. The antibody is opsonic for the target larvae, but is not detectably cytophilic. It is associated with IgG-rich fractions after DEAE-cellulose chromatography, and is removed by anti-IgG immunoadsorbents. In studies on the specificity of the antibody, it was found that activity was also removed by absorption with whole schistosomula, but not with an insoluble adult worm membrane preparation. In this preparation, however, membrane antigens may have been masked; and immunofluorescence studies showed that absorption with schistosomula was associated with loss of activity against the adult worm membrane, indicating a cross-reactivity between schistosomular and adult worm antigens. A finding that activity was also lost after incubation of sera with soluble adult worm antigens was possibly attributable to the formation of immune complexes which blocked effector cell activity. In further studies, it was shown that preincubation of effector cells with exogenous immune complexes resulted in a loss of cytotoxic activity, supporting the hypothesis that Fc receptors are involved in the initial interaction between eosinophils and antibody-coated larvae. The blockade of eosinophil-enriched effector cells by immune complexes was not reversed by washing and subsequent overnight culture before assay. A possible relationship between circulating immune complexes and the relative inactivity of cells from patients with schistosomiasis and eosinophilia is discussed.