Thrombopoietin production by human embryonic kidney cells in culture

Human embryonic kidney cells were maintained in culture in a medium containing lactalbumin hydrolysate for 5 to 6 weeks and the supernatant fluid tested for thrombopoietin content. Thrombopoietin was determined by a bioassay procedure which utilized mice that were in rebound thrombocytosis. The results indicate that the medium from kidney cells in culture contained a factor that stimulates thrombopoiesis in assay mice as measured by per cent 35-S incorporation into platelets. A dose-response relationship was demonstrated between the volume of thrombopoietically active production medium injected and the level of isotope that subsequently appeared in the circulating platelets. Thrombopoietin was not found in control production media. Moreover, thrombopoietin-rich production medium did not contain erythropoietin, erythroginin, or white blood cell-stimulating factors. The results of this study indicate that kidney cells in culture produce a specific thrombopoietic stimulating factor. It seems probable from these in virto data that a site of production of thrombopoietin in vivo is the kidney.