In vitro effect of immune serum and bovine granulocytes on juvenile Fasciola hepatica.

Cattle, infected with Fasciola hepatica metacercariae, produce antibodies against the outer glycocalyx of freshly excysted juvenile F. hepatica. Using 51Cr-release and viability assays such antibodies in the presence or absence of bovine complement did not cause discernible damage to the parasite. The presence of excess antibody caused the build-up of large aggregates of antigen--antibody complexes over the parasite surface; these aggregates were eventually shed into the medium. Neutrophils and eosinophils were obtained by selective stimulation of the mammary gland of heifers, and attached in large numbers to flukes coated with either IgG1 or IgG2. Attachment was dependent on Fc receptors although the adherence of the eosinophils was more prolonged than that of the neutrophils. Using 51Cr-release and viability assays no damage occurred to the flukes using either eosinophils or neutrophils in antibody-dependent cell-mediated cytotoxicity; adherent granulocytes were eventually shed. It is suggested that the rapid turnover and excretion of the outer glycocalyx of juvenile flukes prevents the intimate attachment of granulocytes to the helminth parasite, which is perhaps a prerequisite for cell-mediated damage to occur.