Megakaryocytic colony formation (CFU-Meg) in essential thrombocythemia: quantitative and qualitative abnormalities of bone marrow CFU-Meg.

For the purpose of examining the mechanisms for the overproduction of megakaryocytes and platelets in essential thrombocythemia (ET), marrow megakaryocytic colony-forming units (CFU-Meg) were characterized using a methylcellulose culture system in nine patients with ET, and they were compared with those of 16 control subjects and four patients with secondary thrombocytosis (ST). The number of CFU-Meg per 10(5) cells in ET was significantly higher (p less than .001) than that in the controls (5.8 times of the controls) or that in ST. ET showed endogenous CFU-Meg (58 +/- 16% of the total CFU-Meg) that could form megakaryocytic colonies without phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM) as a source of Meg-CSA. The controls and the patients with St revealed no endogenous CFU-Meg. The dose-response studies with PHA-LCM revealed that CFU-Meg from ET are highly sensitive to low concentrations of PHA-LCM compared to CFU-Meg from the control and ST. Erythropoietic burst-forming units (BFU-E) were monitored as a control progenitor, because the patients with ET studied did not have erythrocytosis. Although five out of nine patients with ET had endogenous BFU-E, the percentages of endogenous BFU-E were small (4-10%). The number of BFU-E in ET was not different from the control value. Thus, ET is associated with an enlarged CFU-Meg compartment that shows abnormal growth patterns when cultured in vitro, while the growth abnormality of BFU-E is small, which may underlie the hematological features of ET. The culture of CFU-Meg should be clinically useful for differentiating ET from ST.