Patterns of in vitro BFU-E proliferation in different forms of polycythaemia and in thrombocythaemia

To investigate erythroid colony formation in polycythaemia of different types and in thrombocythaemia, a study was performed in 121 subjects, including 13 normal volunteers (N), 30 patients with Primary Proliferative Polycythaemia (PPP), 35 with Idiopathic Erythrocytosis (IE), 19 with Secondary Polycythaemia (SP), 10 with Primary Thrombocythaemia (PT) and 14 with Secondary Thrombocytosis (ST); BFU-E colony formation from peripheral blood samples was studied in the presence of medium only, medium plus a source of burst-promoting activity (BPA) and medium BPA, plus erythropoietin (Ep). In the presence of medium only, practically no colonies were seen in cultures from N and SP, while a variable number was observed in cultures from PPP, IE and PT. Significant differences between groups were as follows: N v PPP; IE v PPP; SP v PPP; N v PT; ST v PT. Such differences persisted in the presence of BPA, but disappeared when Ep was added to the cultures. Further experiments, plating non-adherent mononuclear cells in a chemically defined serum-free medium, confirmed the growth of tiny erythropoietic colonies from circulating stem cells of patients with PPP and PT, in the absence of BPA and EP. These results provide a useful criterion to differentiate PPP, as a group, from other types of polycythaemia; individual cases of IE may need further characterization.