Antibody response in cattle, sheep and rats to infection with gamma-irradiated metacercariae of Fasciola hepatica.

Cattle, sheep and rats were infected orally with gamma-irradiated (4 krad) metacercariae of fasciola hepatica, or with normal metacercariae. The antibody response was monitored in each host to metacercarial tegument (T0), juvenile tegument (T1), adult tegument (T2) and gut antigens. The response was examined at weekly intervals for cattle and sheep throughout 15 weeks of infection and four weeks after infection in rats, using an indirect fluorescent antibody labelling technique. It was found that the irradiated metacercariae engendered a normal humoral response to T0, T1 and gut antigens in all three hosts although the antibody levels were somewhat reduced due to an early death or stunting of the flukes. T0 and T1 appeared to be antigenically similar. Antibodies against T2 appeared late in the animals infected with gamma-irradiated metacercariae and the titres attained were considerably lower than in the controls. the T2 antigen stimulus in the animals given gamma-irradiated metacercariae was probably provided by flukes which 'broke through' the developmental barrier imposed by irradiation and which were found alive at autopsy.