Further characterization of the 38 kDa antigen from Echinococcus granulosus (hydatid disease) cyst fluid: evidence for antigenic heterogeneity and reactivity with anti-P1 antibodies.

A panel of 5 IgM and 6 IgG1 monoclonal antibodies (MoAbs) was produced against a band, eluted from a reducing SDS-PAGE gel, containing the 38 kDa subunit of antigen 5 (Ag 5) from Echinococcus granulosus cyst fluid; seven of the MoAbs were shown subsequently to bind epitopes on Ag 5 but none recognized phosphorylcholine or periodate-sensitive carbohydrate epitopes. Differences in the fine specificity of the MoAbs were apparent and, upon reduction, heterogeneity in 38 kDa components from hydatid cyst fluids of different intermediate host origin was revealed by peptide fingerprinting and immunoblotting using the MoAbs. One of the IgG1 MoAbs (ED9) was able to distinguish a reduced 38 kDa molecule in cyst fluids from two distinct genotypes--the horse/dog and sheep/dog strains--of E. granulosus and this may have implications for hydatid serology, immunoepidemiology and strain typing. Furthermore, epitopes on this 38 kDa component or on a different molecule with the same or similar M(r) are reactive with anti-P1 blood group antigen antibodies and this could result in false-positive reactions where sera from P2 patients with suspected hydatid disease are tested by immunoblot or immunoprecipitation analysis.