Stimulation of CFU-Mk colony growth by normal plasma and plasma from myelodysplastic patients.

The ability of plasma from myelodysplastic patients to support the clonal growth of normal megakaryocyte progenitors (CFU-Mk) was compared with that of plasma from normal subjects. The resultant megakaryocyte colonies were expressed as a plasma factor index megakaryocyte (PFI-Mk). All cultures included PHA-LCM and medium conditioned by the human bladder carcinoma cell line 5637, and some of them had EPO. PFI-Mk (MDS) was significantly lower than PFI-Mk (normal), both with and without EPO. A positive correlation was found between megakaryocyte and platelet count in normal subjects, but was not present in MDS patients. There was no correlation between platelet count and PFI-Mk in neither group. In MDS there was a negative correlation between megakaryocyte number and PFI-Mk, both with and without EPO. Although, the mean megakaryocyte number in MDS and in normal bone marrow was similar, the proportion of immature megakaryocytes was much higher in MDS. Previous work indicates an abnormal clonal origin of megakaryocytes in MDS. The present study suggests that abnormal plasma factors affects megakaryocytopoiesis in this condition.