IDENTIFICATION AND DIAGNOSTIC-VALUE OF A MAJOR ANTIBODY EPITOPE ON THE 12 KDA ANTIGEN FROM ECHINOCOCCUS-GRANULOSUS (HYDATID-DISEASE) CYST FLUID

An IgG1 monoclonal antibody (MoAb), designated C9E7H8, has been produc ed against an epitope on the 12 kDa antigen of Echinococcus granulosus cyst fluid, believed to represent the smallest subunit of antigen B. This MoAb, raised against purified 12 kDa antigen eluted from a reduci ng SDS-PAGE gel, demonstrated strong binding to native sheep cyst flui d in ELISA and recognition of all three subunits of antigen B (at 12, 16, 23 kDa) by immunoblot under both reducing and non-reducing conditi ons. Immunoblot analysis also indicated that the complementary epitope is conserved amongst cyst fluids from different intermediate hosts of E. granulosus, including fluids from cysts of two distinct strains, a nd is present in cyst fluid from E. multilocularis. The monoclonal dis plays binding to a cDNA clone, EgPS-3, which we have previously shown expresses part of the 12 kDa molecule. EgPS-S, expressed as a glutathi one-S-transferase fusion protein, was successful in positive detection of 74% of cystic hydatid patients, although cross-reactions were obse rved with 25% of sera from alveolar hydatid and 22% of sera from schis tosomiasis japonica patients. Three peptides, based on the predicted a mino acid sequence of EgPS-3, showed increased specificity but slightl y reduced sensitivity in the detection of antibody from E. granulosus patients. The predominant epitope recognized by human antibody occurs in the N-terminal 27 amino acids (peptide 65) of EgPS-3 which also cor relates with the location of the monoclonal antibody epitope.