Identification of functional Fasciola hepatica antigens in experimental infections in rabbits.

Studies done comparing the reactivity of serum from an infected rabbit at different intervals of infection with a Fasciola hepatica crude tegument extract, F. hepatica excretory-secretory (ES) products and Fh arc 2 by ELISA show that the first 2 antigen preparations offer a better sensitivity for detecting acute infection, especially in its early stages (3 weeks). The ES proteins from F. hepatica adult worms were identified by the enzyme-linked immunotransfer blot (EITB) in order to define the antigens recognized by the sera from rabbits with experimental fascioliasis. A group of 7 polypeptides with molecular weights of 23-28 Kd were the major antigens recognized. Reactivity to these antigens is maximum at 8-10 weeks of infection by EITB. As the infection progresses, reactivity to the 23-28 Kd antigens decreases but does persist through 52 weeks of infection. At least 5 other polypeptides of 120, 84, 58, 52, 39 and 33 Kd were recognized by the sera of infected rabbits from 6 to 52 weeks of infection. A different pattern was observed in parallel studies done with these same sera by immunoprecipitation of ES antigens. In addition to a 33 Kd antigen, which was detected by both techniques, a 62 Kd antigen was detected early in infection (5 weeks) and 3 major antigens of 38, 40 and 44 Kd were prominent by immunoprecipitation from 9 weeks onward. This implies the presence of multiple Fasciola antigens with serodiagnostic potential. The expression of these antigens during development and their possible role in immunity is discussed.