Fasciola hepatica: IgG and IgA levels in the serum and bile of infected cattle

Bile and serum samples were collected from calves with an implanted cannula throughout a 20-week period of infection with Fasciola hepatica. Using indirect fluorescent antibody labelling and plastic-embedded sections of juvenile and adult flukes as antigens, estimates were made of the relative concentrations of IgG and IgA specific for fluke tegumental and gut antigens in the samples of serum and bile. In serum, antibodies against juvenile (t1) tegument and gut antigens reached peak concentrations 4–6 weeks postinfection and declined slowly thereafter as flukes became established in the bile ducts. IgG against adult tegument (t2) antigens appeared in the serum 6 weeks after infection, but no IgA against t2 was detected. In the bile, both IgG and IgA titres against t1 and gut antigens rose to peak values at 4–6 weeks after infection, but there was no activity against t2 antigen. The Ig levels in bile were considerably lower than in serum. Much more IgA relative to IgG occurred in bile as compared to serum (IgG/IgA ratio in serum was 16–32, in bile 1–2) suggesting a role for IgA in defence at mucosal surfaces. Comparison of the antibody profiles in bile and serum suggested that IgG in the bile was derived from circulating IgG whereas IgA may have been preferentially concentrated in the bile.