Production and application of monoclonal antibodies to human selenoprotein P

Selenoprotein P is a selenium-rich extracellular protein and is the major selenoprotein in plasma. Although the biological function of selenoprotein P has not been established, we have recently shown that selenoprotein P has phospholipid hydroperoxide glutathione peroxidase-like activity. To study the structure and function of selenoprotein P, we produced monoclonal antibodies against human selenoprotein P. Immunization of rats with purified selenoprotein P was followed by hybridization, cloning, and the establishment of eleven hybridomas producing specific antibodies against human selenoprotein P. With the addition of six kinds of insoluble rat anti-human selenoprotein P monoclonal antibodies to human plasma, the selenium concentration of the supernatant was decreased to 47% of the control. This suggests that selenoprotein P constituted 53% of total plasma selenium. Western blot analysis of the immunoprecipitate from human plasma showed that the antibodies specifically bound to a 69 kDa protein, representing selenoprotein P. Next, we developed an enzyme-linked immunosorbent assay for selenoprotein P using two monoclonal antibodies. The plasma concentration of selenoprotein P in 77 normal individuals was 5.3 ± 1.1 μg/ml. Because preferential depletion of selenoprotein P by low density lipoprotein (LDL)-apheresis has been reported, we next measured selenoprotein P concentration of plasma samples from patients before and after LDL-apheresis. We confirmed that the plasma concentration of selenoprotein P was decreased from 5.7 to 2.3 μg/ml by LDL-apheresis. This result shows that this assay provides a reliable means of measuring the content of selenoprotein P in plasma.