Monoclonal antibodies to human urinary thrombopoietin

Monoclonal antibodies (MA) to a thrombocytopoiesis-stimulating factor (TSF or thrombopoietin) were obtained from hybridomas derived from the fusion of P3 x 63/Ag 8 cells and spleen cells from TSF-immunized BALB/c mice. Media from several hybrid cultures were tested in a microantibody detection technique that measured the binding of MA to a 125I-purified TSF preparation from human embryonic kidney (HEK) cells. Hybridized cells were injected into pristane-primed mice and the antibodies produced in the ascites fluid were also shown to bind the 125I-TSF. Compared to the results of normal mouse serum, ascites fluid containing MA was shown to bind the unlabeled TSF from HEK cells. The TSF activity was significantly reduced in the supernatant fluid after precipitating the TSF-anti-TSF immune complex by a second antibody when tested in an immunothrombocythemic mouse assay. After SDS-PAGE, the precipitate from this TSF-Ma conjugate showed that the antiserum bound a single 32,000 mol wt component, indicating the monospecificity of the MA. MA directed toward human TSF will allow studies that were not previously possible