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

Summary. 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.