Interactions between human eosinophils and schistosomula of Schistosoma mansoni. I. Stable and irreversible antibody-dependent adherence.

Abstract The adherence of purified eosinophils (mean purity 93%) and neutrophils (mean purity 94%) from normal, noneosinophilic subjects to schistosomula of Schistosoma mansoni was examined. Significant adherence occurred only in the presence of human anti-schistosomular serum. Eosinophil adherence was greater than neutrophil adherence at all times of incubation and at all concentrations of cells or of anti-schistosomular serum. An IgG fraction of anti-schistosomular serum was sufficient to mediate this adherence. Addition of Staphylococcus aureus protein A (SPA) (63 μg/ml) or of aggregated human γ-globulin (aHGG) (2.5 mg/ml) at the beginning of the incubation inhibited the adherence reaction, suggesting that the cells bound via their receptor for the Fc portion of immunoglobulin (FcR). Several unusual features of eosinophil adherence were noted that were not explicable on the basis of classical FcR-dependent reactions. First, eosinophil adherence at 37°C was better than neutrophil adherence in spite of the higher density of FcR on neutrophil membranes as assessed by rosette formation. Secondly, eosinophil adherence was greatly reduced at 4°C, whereas neutrophil adherence was essentially unchanged. In contrast, FcR-mediated binding of eosinophils to antibody-coated red cells was stronger at 4°C than at 37°C. Thirdly, although incubation at 4°C inhibited the initiation of eosinophil adherence, it was not capable of reversing established adherence. Fourthly, SPA and aHGG, although capable of inhibiting the initiation of eosinophil and neutrophil adherence, were ineffective in reversing established eosinophil adherence to schistosomula, whereas established neutrophil adherence was easily reversed. These results indicate that antibody-dependent eosinophil adherence proceeds in at least two distinguishable steps. The first is mediated by FcR, and is relatively weak, whereas the second, a temperature-dependent step, allows a firm, relatively irreversible binding of the eosinophil to schistosomula. This mechanism would ensure the selective concentration of eosinophils on the surface of schistosomula. In this system, eosinophils, but not neutrophils, then proceed to kill the parasite.