Purification and partial characterization of the major antigen of Echinococcus granulosus (antigen 5) with monoclonal antibodies

A monoclonal antibody specific for antigen 5 of Echinococcus granulosus was isolated and partially characterized. Purification of antigen 5 was accomplished by affinity chromatography using an immunoabsorbent prepared with this monoclonal antibody. Pure antigen 5 was identified by immunoelectrophoresis, double diffusion in agar gel, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting. The pure antigen displayed the electrophoretic mobility typical of antigen 5 and gave a single precipitin band in double diffusion with both monoclonal antibody and rabbit anti-pH5PPT hydatid fraction serum. Two bands of 66 and 56 kDa could be detected in the pure antigen 5 after sodium dodecyl sulphate-polyacrylamide gel electrophoresis when performed in non-reducing conditions: both bands were reactive with the monoclonal antibody in immunoblotting. After reduction with 2-mercaptoethanol, antigen 5 displayed one band only, of 39 kDa. Antigen 5 purified by this procedure was found to retain reactivity with human sera from hydatid patients in a DD5 test.