Characterization of monoclonal antibodies recognizing alpha and beta subunits of human chorionic gonadotropin hormone.

Human chorionic gonadotropin (hCG) hormone is required for maintenance of early pregnancy and is a potential marker in the diagnosis and prognosis of both pregnancy and trophoblastic diseases. Murine hybridomas were generated against purified hCG. Seven hybrid clones secreting antibodies against hCG molecule with IgG1/kappa subclass were established. The indirect ELISA result demonstrated that six MAbs (BEL-1 to BEL-6) recognized hCG in both holo and free beta subunit form with negligible cross-reactivity against a closely related hormone, human luteinizing hormone (hLH). In this fusion, only one MAb (ALC-1) showed a cross-reaction with hLH, which designated an alpha subunit specific. The outcome of Western blot ascertained that ALC-1 recognized the conformational epitope on alpha subunit of hCG at Mr 23 kDa band in nonreducing condition (NR). In contrast, epitopes belonging to all MAbs recognized beta subunit of hCG were in linear peptide structure at Mr 34 kDa band (NR) and Mr 26 kDa band (R). These six MAbs were further characterized by using two beta subunit carboxy-terminal synthetic peptides (beta109-119 and beta109-145). Three of them (BEL-1, BEL-3, and BEL-4) recognized only epitope harboring in beta109-145 fragment, the others recognized both types of the synthetic peptide. In order to select the most suitable MAbs specific to beta subunit of hCG for exploiting with ALC-1 in the sandwich-type immunometric assay, competitive ELISA was employed. Six individual MAbs specific to beta subunit of hCG were used to compete with biotinylated ALC-1 to evaluate the proximity of their epitopes on the holo form of hCG molecule. Of all six MAbs, BEL-5 depicted the lowest percent inhibition result, which indicated the bottom-most steric hindrance effect. Consequently, MAb BEL-5 will be the most appropriate antibody to utilize in concert with ALC-1 in place of devising a sandwich-type immunometric assay for measuring holo-hCG level.

Construction, purification and characterization of a recombinant baculovirus containing the gene for alpha subunit of human chorionic gonadotropin.

A cDNA encoding the alpha subunit of human chorionic gonadotropin, a placental glycoprotein hormone, was cloned downstream to the viral polyhedrin gene promoter of Autographa california nuclear polyhedrosis virus and the recombinant transfer vector was used to co-transfect Spodoptera frugiperda cells growing in culture. Recombinant baculovirus carrying the alpha hCG gene was detected and isolated after dot hybridization using supernatant from co-transfected cells. Recombinant vAc alpha hCG having a replacement of the viral polyhedrin gene, which is hyper-transcribed very late in the infection cycle, with the alpha hCG cDNA was purified after a single round of plaque purification. Insect cell culture infected with vAc alpha hCG, secreted high levels of hCG which was biologically active.