EXPRESSION AND ANALYSIS OF THE DIAGNOSTIC-VALUE OF AN ECHINOCOCCUS-GRANULOSUS ANTIGEN GENE CLONE

A pool of 9 sera from Echinococcus granulosus infected patients (PSP) was used to screen an E. granulosus cDNA library constructed in the ex pression vector lambda gt11. Ten reactive phage clones were isolated a nd 8 were confirmed in spot-lysis arrays probed with PSP. The insert o f 1 of these clones (lambda AgEg4) previously characterized as an E. g ranulosus cytosolic malate dehydrogenase encoding gene was subcloned i nto the plasmid vector pGEX-1 and expressed as a fusion with glutathio ne S-transferase. The fusion peptide (Ag4-GST) was produced in Escheri chia coli and its antigenicity was confirmed in colony immunoassay and in immunoblot using nondenaturing conditions. The lack of antigenicit y of Ag4-GST in immunoblot using denaturing conditions suggests that t he recognized epitopes are conformational. Ag4-GST was purified by aff inity chromatography and tested in ELISA and immunodots to access its sensitivity and specificity in the diagnosis of human cystic hydatid d isease. An overall sensitivity of 53.6% was obtained. Cross-reactions were observed with some sera From patients infected with Schistosoma m ansoni and Wuchereria bancrofti. Ag4-GST was not recognized by any of the sera from Taenia solium infected patients tested. These preliminar y results suggest that Ag4-GST could be useful as an accessory antigen to discriminate some cross-reactions with sera from cysticercosis pat ients, especially in regions like southern Brazil, where schistosomias is and Filariasis are not prevalent.