An ultrastructural study of the interaction of human eosinophils with respiratory syncytial virus

It was shown previously that eosinophils are activated in vivo and in vitro by respiratory syncytial virus (RSV). For study of the interaction of eosinophils and RSV on the ultrastructural level, normodense eosinophils were purified from peripheral blood of healthy human volunteers. After incubation with RSV in the presence or absence of autologous serum, the eosinophils were examined with immunofluorescence microscopy employing an RSV-specific monoclonal antibody, and with transmission electron microscopy. After 2-h incubation in the presence of live RSV, 25.6 ± 12.9% of the eosinophils demonstrated positive fluorescence. This increased to 62.8 ± 8.9% when fresh autologous serum was added during incubation (P = 0.015). The effect was abolished when the serum was heat-treated, indicating Fc-receptor-independent enhancement of viral uptake by the cells. In transmission electron microscopy, virions were seen in phagocytic vacuoles at the periphery of the cells. Eosinophil activation characterized by piecemeal degranulation was evident. In conclusion, activation of eosinophils during RSV bronchiolitis probably occurs in part by direct interaction of the cells with the virus.