The identification of a Clonorchis sinensis gene encoding an antigenic egg protein.

The cDNA library of Clonorchis sinensis was screened for genes encoding antigenic proteins by using sera from clonorchiasis patients. A gene of 888 bp encoding a 28-kDa protein (Cs28) was cloned and found to contain a high percentage of glycine (20%), tyrosine (11%), and lysine (11%). The amino acid sequence of Cs28 showed 60% homology with the vitelline B precursor protein of Opisthorchis viverrini and of 33% homology with the vitelline B1 and B2 proteins of Fasciola hepatica. A strong positive reaction was observed in the intrauterine eggs of adult C. sinensis by immunohistochemical analysis using specific immune sera against recombinant Cs28 protein (rCs28). By immunoblot analysis, rCs28 displayed an antigenic reaction with 73% of the serum samples from 115 cases of clonorchiasis. In addition, it cross-reacted with the sera of 77.5% of 40 opisthorchiasis cases, 90% of 20 schistosomiasis cases, and 50% of 10 paragonimiasis cases. However, no cross-reactions were observed with the sera of sparganosis or cysticercosis patients. In conclusion, the Cs28 protein was identified as an egg protein of C. sinensis and as an antigen common to the trematode species examined.