Acquired aplastic anaemia: a PNH-like disease?

Bone marrow from 20 patients with aplastic anaemia at different stages of disease and from three patients with paroxysmal nocturnal haemoglobinuria (PNH) was incubated in isosmolar sucrose with 5% autologous serum prior to culture in methylcellulose. If fresh serum was used, colony formation by granulocyte-macrophage colony forming cells (GM-CFC) and immature erythroid precursors (BFU-E) was reduced to approximately 50% in all patients tested, at any stage of disease, including complete autologous bone marrow recovery. Heat inactivation and complement inactivation with EDTA completely abrogated this inhibitory serum effect. Selective inactivation of the classical, antibody dependent complement pathway with Mg2+ EGTA reduced the inhibitory effect by 50%. Complement sensitivity of haemopoietic precursors is a known feature of PNH. Since the majority of our patients did not have PNH as judged by a negative sucrose-test on mature erythrocytes, we conclude that, in aplastic anaemia, haemopoietic cells express a PNH-like defect at a primitive level.