Ultrastructural observations on the interaction in vitro between bovine eosinophils and juvenile Fasciola hepatica.

This ultrastructural study has shown that there is a layer of dense flocculent material on the surface of juvenile Fasciola hepatica incubated in vitro with specific bovine antiserum. This material corresponds to the complexes of secreted glycocalyx and bovine antibody previously characterized by fluorescence microscopy. Bovine eosinophils attach closely to those regions of the parasite's surface that are free of flocculent precipitates. This close attachment is followed by degranulation of the eosinophils into the narrow zone between the cells and the parasite. Only in these regions is damage, in the form of vacuolation of the tegument, seen within the juvenile F. hepatica. It is concluded that the inability of bovine eosinophils to kill juvenile F. hepatica in the presence of specific antiserum results from the presence of a protective layer, consisting of antigen/antibody complexes, on the parasite's surface.