Partial characterisation of carbohydrate-rich Echinococcus granulosus coproantigens

Coproantigen ELISA based tests for diagnosis of canine echinococcosis provide high specificity and sensitivity. However, the antigenic molecules present in faeces from infected dogs have not yet been characterised. While initial attempts to determine the molecular weights of Echinococcus granulosus coproantigens by SDS-PAGE and Western blotting with coproantigen reactive capture antibodies were equivocal, they suggested presence of a significant carbohydrate component. Periodate treatment of coproantigen positive faecal supernatants resulted in a significant reduction (53%) in ELISA activity, suggesting that carbohydrates are involved in the antigenic structure of E. granulosus coproantigens. Protease treatment of antigenic molecules resulted in an 11% reduction in absorbance in ELISA, indicating that protein components were also present which affected by enzyme activity. Lectin-binding ELISA assays indicated strong affinity of E. granulosus coproantigens to concanavalin agglutinin and Lens culinaris agglutinin, and moderate binding to wheat-germ agglutinin and peanut agglutinin. No binding was detectable to Ulex europaensis agglutinin-I, Bandeiraea simplicifolia or Dolichos biflorus agglutinin. These data indicate that E. granulosus coproantigens from infected dog faeces possibly contained alpha-D-mannose and/or alpha-D-glucose, beta-galactose and N-acetyl-beta-glucosamine residues. To verify the role of carbohydrate moieties in coproantigens, faecal samples were treated with exoglycosidase and tested in the coproantigen ELISA. Treatment with beta-galactosidase or N-acetyl-beta-glucosamine reduced ELISA activity by 44 and 30%, respectively. Incubation with a panel of other specific exoglycosidases including alpha-galactosidase as well as alpha-L-fucosidase, alpha-mannosidase, beta-mannosidase, alpha-glucosidase, beta-glucosidase, beta- fructosidase, or neuraminidase, did not alter coproantigen detection in ELISA. The results indicate that coproantigens present in faeces from E. granulosus naturally infected dogs were highly glycosylated and contain beta- galactose and N-acetyl-beta-glucosamine. The putative relationship of antigenic molecules with the tapeworm glycocalyx is discussed.