Immunophenotypic discrepancies between granulocytic and erythroid lineages in peripheral blood of patients with paroxysmal nocturnal haemoglobinuria

Abstract: In paroxysmal nocturnal haemoglobinuria (PNH), somatic mutation of the PIG‐A gene is thought to result in altered expression of glycosylphosphatidylinositol (GPI)‐anchored proteins. This study was performed to determine if there were any heterogeneities of cellular phenotypes between two major peripheral blood cells, erythrocytes and granulocytes. Using CD59‐based immunocytometry, the patterns of CD59 expression were shown to be conserved in the circulating erythroid cells (reticulocytes and mature erythrocytes) in all 29 patients with PNH. Twenty‐one patients had distinct combinations of PNH type I, II, and III cells in different lineages. Only eight patients exhibited similar patterns of CD59 expression between the two lineages. Approximately one third of the patients had PNH type II cells in either or both of the two lineages indicating variable lineage involvement. The proportion of abnormal granulocutes was higher than those of abnormal reticulocytes and erythrocytes. In patients with appropriate erythropoietic responses to haemolysis (RPI>2.0), shift reticulocytes display predominantly PNH phenotypes. These immature erythroid cells with altered expression of GPI‐anchored proteins may dominate the peripheral blood during periods of increased marrow activity resulting in greater phenotypic mosaicism in such patients. Discrepancies in expression of GPI‐anchored proteins in PNH which are highly variable between the two lineages may be the result of their different life spans and the influence of complement‐mediated cytolysis. The phenomena also indicated the possible occurrence of more than one PNH clones with variable clonal dominance.