Monoclonal Antibodies Against Immunodeterminants Associated with the Alpha and Beta Subunits of Human Chorionic Gonadotropin

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Abstract
Spleen cells of BALB/c mice immunized with human chorionic gonadotropin (HCG), a glycopeptide hormone composed of two nonidentical α and β subunits, were fused with NS-1 mouse myeloma cells. Two hybrid cell lines, clone PC2 and clone PD3 secreting monoclonal antibodies (McAb) to HCG were isolated. With the aid of a double antibody radioimmunoassay it was established that PC2-McAb recognizes an immunodeterminant associated with β-HCG subunit, whereas, PD3-McAb recognizes an epitope present on the α-HCG subunit. Both monoclonal antibodies showed an affinity constant of approximately 5 × 1010 L/M. Because of these immunological characteristics, only PC2-McAb specifically reacts with HCG and shows cross-reactivities of less than 0.1% to other related human glycopeptide hormones. On the other hand, using a hemagglutination test based on antibody induced agglutination of sheep red blood cells coated with HCG, it was shown that only PD3-McAb is capable of inducing a positive reaction, although both monoclonal antibodies have a similar binding capacity to the coated cells. The potential of these two new monoclonal reagents for the qualitative detection and quantitative determination of HCG in human biological fluids is discussed.