Proliferation of erythroid colonies in semi-solid agar.

Growth of human erythroid cells in soft-agar culture with no added erythropoietin was demonstrated. This growth was particularly marked in patients with diseases such as myelofibrosis (MF) in which patients had a previous history of polycythaemia vera (PV) characterized by excessive red cell production. A rapid assessment of the proportion of erythroid colonies was obtained by directly staining the culture with benzidine. Fixed and stained preparations of these agar-grown cells revealed elements in all stages of erythroid maturation. The morphology of these erythroid colonies was characteristic of 'erythroblastic islands' containing central, iron-containing macrophages, surrounded by erythrocytic precursors, with the more mature erythrocytes found at the periphery of the colony. These observations document that erythropoiesis may be maintained in agar cultures, and suggest that this technique may be of diagnostic value in disease states characterized by abnormalities of red cell production.