The diagnostic value and molecular characterisation of an Echinococcus multilocularis antigen gene clone.

A diagnostic Echinococcus multilocularis antigen gene (EM4) has been expressed using the Escherichia coli expression vector pGEX-1 resulting in the high level synthesis of a readily purifiable, soluble, non-denatured peptide fused to the 26-kDa glutathione-S-transferase of Schistosoma japonicum. This recombinant antigen, on testing by enzyme-linked immunosorbent assay (ELISA) with heterologous human antisera, demonstrated 100% E. multilocularis specificity. Specific anti-EM4 antibody immunoprecipitated a single 66-kDa protein from protoscolex total RNA directed in vitro translation products indicating the probable involvement of post-translational modification in the production of the native EM4 antigens. Southern blotting analysis suggests that the EM4 native antigens are coded for by a single-copy gene and that the genomic organisation of the EM4 related genes in other parasites is not conserved. The nucleotide sequence of the cloned EM4 cDNA molecule has been obtained and the derived amino acid sequence shows no significant homology with other existing protein sequences.