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Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012, India
¹ Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India

(Requests for offprints should be addressed to R R Dighe; Email: rdighe{at}mrdg.iisc.ernet.in)

Human chorionic gonadotrophin (hCG) is secreted during early pregnancy and is required for implantation and maintenance of the pregnancy. Active or passive immunoneutralization of hCG results in termination of pregnancy and this forms the basis of the hCG-based female contraceptive vaccine. However, the ß subunit of hCG possesses 85% sequence homology with the first 114 amino acids of the ß subunit of pituitary human LH (hLH), which is required for ovulation and maintenance of the corpus luteum function during the menstrual cycle. Immunization against hCG or its ß subunit leads to generation of antibodies that can neutralize hLH due to many shared epitopes and hence may cause abnormal menstrual cycles. Therefore, it is essential to identify epitopes that are different in the two hormones. In the present study, we report a monoclonal antibody (MAb) specific for hCG that shows no binding to the isolated subunits. Interestingly, the MAb also does not bind hLH at all. The epitope mapping analysis revealed that this antibody recognizes a unique discontinuous epitope present only in the heterodimeric hCG and is distinct from the unique C-terminal extension of hCGß that is absent in hLHß. The MAb, either as IgG or its recombinant single-chain variable region fragment, inhibited the response to hCG, but not to hLH. Thus, the epitope recognized by this MAb is an ideal candidate antigen for immunocontraception.

This article has been cited by other articles:

				S. Roy, S. Setlur, R. A. Gadkari, H. N. Krishnamurthy, and R. R. Dighe Translational Fusion of Two {beta}-Subunits of Human Chorionic Gonadotropin Results in Production of a Novel Antagonist of the Hormone Endocrinology, August 1, 2007; 148(8): 3977 - 3986. [Abstract] [Full Text] [PDF]