Suppression of in Vitro Granulocyte-Macrophage Colony Formation by the Peripheral Mononuclear Phagocytic Cells of Patients with Idiopathic Aplastic Anaemia

S ummary . To investigate whether phagocytic cells play a role in the pathogenesis of aplastic anaemia, we studied the effect of the mononuclear phagocytic cells in the peripheral blood from patients with idiopathic aplastic anaemia on granulocyte—macrophage colony (GM-colony) formation. There was no apparent infection in the studied patients. In nine out of 20 cases the mononuclear cells suppressed the formation of GM-colonies by normal bone marrow. Removal of the phagocytic cells by carbonyl iron powder caused a loss of this suppressive effect. These results suggest the requirement for phagocytic cells in this suppressive effect and the possible involvement of phagocyte-mediated immunological mechanism in the pathogenesis of some cases of idiopathic aplastic anaemia.