Improved immunodiagnosis of cystic hydatid disease by using a synthetic peptide with higher diagnostic value than that of its parent protein, Echinococcus granulosus antigen B.

The assays are used for the diagnosis of hydatid disease are still imperfect. The reported diagnostic sensitivity and specificity vary greatly depending on the panel of sera used, the laboratory conducting the assay, and, more critically, the antigen used. To contribute to its standardization, we have recently ranked the diagnostic performances of the major parasite antigens and the available synthetic peptides using a large collection of serum samples. That work showed that antigen B (AgB) possesses the highest diagnostic value among these antigens. In the present work we further dissected its antigenicity by analyzing the reactivity of the same panel of sera against a set of synthetic peptides spanning the sequence of both AgB subunits. The N-terminal extension of these subunits appeared to be immunodominant in human infections. A 38-mer peptide (p176) delineated from the N-terminal extension of the AgB/1 subunit performed in an enzyme-linked immunosorbent assay with a higher diagnostic sensitivity (80%) and specificity (94%) than native AgB, Ag5, or any other peptide antigen tested against this collection of serum samples. In view of its high diagnostic value and its nature as a well-defined reproducible antigen, p176 could conveniently be used as a reference standard antigen in the diagnosis of hydatid disease.