Complement sensitivity of erythroid and myeloid precursors in paroxysmal in nocturnal hemoglobinuria

Megakaryocyte progenitors in paroxysmal nocturnal haemoglobinuria are sensitive to complement

We have investigated growth in vitro of bone marrow megakaryocytic progenitors (CFU-Mk) in 7 patients with paroxysmal nocturnal haemoglobinuria (PNH) to determine the sensitivity of CFU-Mk to complement. Bone marrow light density mononuclear cells were exposed to fresh or heat-inactivated AB human serum in the presence of medium or isotonic sucrose solution. We found that the proliferative activity of bone marrow CFU-Mk in PNH patients was significantly lower than in controls. In addition, the number of CFU-Mk in PNH bone marrow cells exposed to isotonic sucrose and complement was reduced to 25% of that in PNH cells exposed to isotonic sucrose without complement. In conclusion, our finding showed an increased sensitivity of CFU-Mk in PNH bone marrow cells to complement, supporting the hypothesis that the PNH defect is present at the level of CFU-Mk.

Increased sensitivity to complement of megakaryocyte progenitors in paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a haemolytic disorder characterized by an increased sensitivity of peripheral blood cells including platelets to the lytic action of complement (C'). Previous studies have demonstrated that in PNH bone marrow erythroid colony and burst forming units, as well as granulocytic-monocytic colony forming units, have an increased sensitivity to complement-induced injury as compared with normal erythroid and myeloid progenitors. The purpose of this study was to investigate the effect of complement on PNH and normal marrow megakaryocytic progenitors (CFU-M). Bone marrow non-adherent and T-cell depleted light density mononuclear cells from three patients with PNH and six normal volunteers were exposed to fresh or heat-inactivated AB human serum in the presence of medium or isotonic aqueous sucrose solution for 30 min at 37 degrees C. After being washed the cells were assayed for CFU-M by the plasma clot method in a complement free medium containing 6% medium conditioned by T-lymphocytes stimulated by phytohaemagglutinin. The number of megakaryocytic colonies grown from PNH marrow cells exposed to isotonic sucrose and C' was reduced to one third of those grown from PNH cells exposed to isotonic sucrose and heat-inactivated C', or to medium with and without C'. In contrast, the number of megakaryocytic colonies grown from normal marrow cells exposed to isotonic sucrose and C' was unchanged. These findings indicate that PNH marrow CFU-M express an increased sensitivity to C'-mediated injury similar to that detected on PNH-erythrocytes by the sucrose haemolysis test, and support the hypothesis that the PNH defect is expressed at the level of pluripotent haematopoietic stem cell.