Identification of a differentially expressed Echinococcus multilocularis protein Em6 potentially related to antigen 5...

By a strategy of differential immunological screening of an expression library constructed from adult Echinococcus multilocularis parasites, a partial cDNA sequence encoding a protein termed Em6 was isolated. This molecule displayed high sequence homology to the recombinant antigen 'Eg6' which was previously described as an immunogenic epitope of antigen 5 of E. granulosus. Further Em6 sequences and the corresponding sequences from a cattle isolate of E. granulosus were obtained by a PCR approach. By immunoblot analyses using affinity purified antibodies, expression of Em6 in fertile cysts producing protoscoleces of the E. multilocularis metacestode stage was observed. However, Em6 was absent in non-fertile metacestodes. The demonstration of a protein in E. multilocularis displaying identities to 'antigen 6' of E. granulosus could potentially contribute to the future elucidation of the relationship between antigen 5 and 'antigen 6' in the genus Echinococcus, and shed some lights on the performance of serodiagnostic assays for hydatid disease based on the respective antigens.