Identification and expression of a Fasciola hepatica gene encoding a gut antigen protein bearing repetitive sequences.

A Fasciola hepatica cDNA clone of about 2 kb was isolated from an expression library by immunological screening using blood serum from an experimentally infected calf. The cDNA clone hybridised to a RNA of about 3 kb in a Northern blot experiment. The nucleotide sequence of the cDNA revealed the presence of an open reading frame of 1636 bp which encoded 24 tandemly arranged 20-amino acid-long repeats, followed by 65 non-repeated residues preceding the stop codon. This antigen was expressed in Escherichia coli as beta-galactosidase fusion proteins which were used for the production of specific antibodies. Immunofluorescence studies using specific antifusion sera revealed that the antigen was specifically expressed in the parasite intestine epithelial cells. Due to its early appearance it might be possible to design diagnostic assays based on this repeated antigen for identification of recently infected animals.