IMMUNOPHENOTYPIC ANALYSIS OF RETICULOCYTES IN PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA

The hematologic disorder paroxysmal nocturnal hemoglobinuria (PNH) occ urs following an acquired somatic mutation in the Piga gene within a b one marrow stem cell. The progeny of this mutated cell cannot synthesi ze glycosylphosphatidylinositol (GPI) anchors, with a resultant defici ency in surface expression of all GPI-linked proteins. The protean cli nical manifestations of PNH presumably result from the deficiency of t hese GPI-linked surface proteins. To explain the observation that neut rophils are affected at a significantly higher percentage than circula ting erythrocytes and to analyze the proliferative rates of erythroid production in PNH, we studied 25 patients using flow cytometry. The fl uorescent dye thiazole orange was used to detect reticulocytes, and CD 59 monoclonal antibody was used to identify GPI-deficient cells. In co ntrast to the mature circulating erythrocytes, the percentage of abnor mal reticulocytes was similar to the percentage of affected neutrophil s. However, the vast majority of reticulocytes was completely GPI-defi cient. ie, were type III cells, even in patients with only modest numb ers of circulating type III erythrocytes. In addition, greater than 5% type II reticulocytes were identified in only 3 patients, although gr eater than 5% type II mature erythrocytes were identified in 10 of 25 patients. The results show that the erythroid and neutrophil bone marr ow precursors have an equivalent proliferative advantage in PNH. The d ata also have important implications for the origin of type-II erythro cytes in PNH. (C) 1995 by The American society of Hematology.