Characterization of a monoclonal antibody to human sex hormone binding globulin

We have produced a monoclonal hybridoma cell line (S1B5) that secretes an IgG2α immunoglobulin with a high affinity (Kd 0.38 × 10−11 M) for 125I-labelled sex hormone binding globulin (SHBG), and which will specifically immunoprecipitate SHBG from serum. The antibody is produced in high titre in culture medium and ascites fluid, and can be purified to apparent homogeneity by protein A affinity chromatography. When examined by isoelectrofocussing, a characteristic series of bands, which bind 125I-SHBG, are observed at pH 8.5–9. Competitive, superimposable displacement of 125I-SHBG from the antibody is achieved with dilutions of human, chimpanzee and gorilla sera at comparable SHBG concentrations. Partial cross-reaction is observed with sera from other Old World primates, but not with sera from New World monkeys or any other vertebrate species studied.