Complement sensitivity of erythroblasts and erythropoietic precursors in paroxysmal nocturnal haemoglobinuria (PNH).

To clarify the regulation of erythropoiesis of complement (C')-sensitive erythrocytes (E) during erythroid cell maturation and differentiation in paroxysmal nocturnal haemoglobinuria (PNH), the C' sensitivity of (1) erythroblasts from erythropoietic bursts and (2) erythropoietic precursors was examined in seven patients with PNH. For the former, a modified complement lysis sensitivity (CLS) test using the trypan blue dye exclusion method was employed. For the latter, an erythropoietic cell culture following the CLS or sucrose haemolysis (SH) test for mononuclear cells was used. Linear relationships were found between the concentrations of C' and proportions of C'-mediated haemolysed erythroblasts in both PNH and normal erythropoietic bursts. In addition, PNH erythroblasts showed hypersensitivity to C'; in the C' dilution for 50% lysis was 12.5 +/- 8.1 ml in PNH patients and 42.3 +/- 4.5 ml in normal controls. There was also a significant correlation (r = 0.919; P less than 0.01) between the proportions of PNH-III E and haemolysed erythroblasts. Significant hypersensitivity of mature erythroid progenitors (CFU-E) to C' was found in both the SH (P less than 0.01 or P less than 0.05) and CLS (r = -0.712; P less than 0.001) tests in PNH patients. However, no hypersensitivity to C' was observed at the primitive erythroid progenitors (BFU-E) level in either the PNH patients or the normal controls. These findings suggest that in PNH the property of C' sensitivity appears during differentiation and maturation from BFU-E to CFU-E and that the proportions of PNH-III E are already programmed at the level of erythroblasts.