Use of a monoclonal antibody specific for a protein epitope of Echinococcus granulosus antigen 5 in a competitive antibody radioimmunoassay for diagnosis of hydatid disease.

A monoclonal antibody (mAb) designated as EG 02 154/12, specific for the major antigen (antigen 5) of Echinococcus granulosus was produced, and used to study the binding sites recognized by anti-antigen 5 antibodies from patients with hydatid disease. The nature of the target epitope was partially characterized. The antibody reactivity was analyzed towards sheep hydatid fluid antigens (SHF Ag) using ELISA, immunoelectrophoresis (IEP), Western blotting (WB), and immunoprecipitation (IP). In IEP, EG 02 154/12 mAb gave a single precipitin of Ag 5. The mAb and human hydatid patient sera recognized a major antigen of 64 kDa, in SHF Ag analyzed in non-reducing conditions. Both types of antibodies revealed two components of 37 and 22 kDa in reducing conditions. Deglycosylation and delipidation of SHF Ag did not affect the mAb binding. These results, together with the observation of mAb binding to in vitro translation products from protoscoleces messenger RNA, suggest the protein nature of the epitope recognized on the antigen 5. Using competitive antibody radioimmunoassay (CRIA), a competition between this mAb and hydatid patient sera, for the same epitope or closely related sites on antigen 5, was observed. No such competition was detected with the sera from other helminthiasis. The sensitivity and specificity of CRIA was compared to that of ELISA and CRIA found to be an improved diagnostic test for hydatid disease.