IMMUNOBLOT EVALUATION OF IGG AND IGG-SUBCLASS ANTIBODY-RESPONSES FOR IMMUNODIAGNOSIS OF HUMAN ALVEOLAR ECHINOCOCCOSIS

Antigen binding of total-IgG and IgG-subclass antibodies from patients with alveolar or cystic echinococcosis (AE and CE) was assessed by im munoblotting. Antigen extracts were prepared from Echinococcus multilo cularis protoscoleces (EmP) or from homogenized E. multilocularis meta cestode tissue (EmCH). Antigens of approximately 44, 35, 27, 21, 17.5 and 16.5 were recognized by total-IgG and IgG,- and IgG(4)-subclass an tibodies in some of 50 human AE sera from China, Japan or France. The 44- and 35-kDa polypeptides, present in both EmP and EmCH extracts, we re recognized by total-IgG antibodies in sera from 82% and 66% of the AE patients, respectively. However, over 30% cross-reactivity occurred between these two antigens and sera from CE and Taenia solium cystice rcosis patients. The immunoblot specificities of the 27-, 21- and 17.5 -kDa antigens in EmP for E. multilocularis infection were 73%, 88% and 93%, respectively. Recognition of the 17.5-kDa antigen in the EmP imm unoblot was much higher for the Japanese AE cases (11/13; 85%) than fo r the French (9/19; 47%) or Chinese (9/18; 50%) AE cases. None of the CE cases from Uruguay or Libya, where human AE has not been reported, was seropositive for the 17.5-kDa antigen. Antibodies from three (7.3% ) of the 41 Chinese CE cases recognized the 17.5-kDa antigen. Within t he 13 Japanese AE sera, the combined detection by IgG(1), IgG(4) and t otal-IgG antibodies of the 27-, 21- and 17.5-kDa antigens in either Em P or EmCH immunoblots was greater than that by each class/subclass alo ne, increasing the overall sensitivity for AE patients. A combined ELI SA/immunoblot approach, including IgG-subclass detection using E. mult ilocularis protocolex or cyst extracts, could be useful for the differ ential diagnosis of human alveolar echinococcosis. An algorithm for su ch an approach is given.