Comparative effects of thrombopoietin and colony-stimulating factors

The possible relationships between thrombocytopoiesis-stimulating factors (TSF or thrombopoietin) and colony-stimulating factors (CSF) were studied. Various CSF-rich preparations and two lots of TSF-rich human embryonic kidney cell culture medium were tested for their ability to stimulate 35S incorporation into platelets of immunothrombocythemic mice. The TSF-rich culture medium produced linear dose-responses between the amount of medium injected and the level of 35S incorporation into platelets of assay mice. Thirteen CSF-rich preparations were used in three separate experiments; the results indicated a lack of correlation (r = 0.003) between CSF activity and the ability of these preparations to stimulate 35S incorporation into platelets of assay mice. Moreover, purified L-cell CSF was inactive in the TSF assay. When the colony stimulating activity in preparations rich in TSF were neutralized with anti-CSF serum, the material's ability to stimulate platelet production in mice was not affected. Based on these results, we conclude that TSF and CSF are separate entities.