Phenotypic analysis of affected peripheral erythroid for CD59 in paroxysmal nocturnal hemoglobinuria

To determine whether affected reticulocytes could be a reliable marker for the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH), we analyzed CD59-antigen expression on the membranes of reticulocytes and erythrocytes.

We studied 10 PNH patients and 5 healthy volunteers by two-color flow cytometry with a membrane permeable fluorescent dye, thiazole orange (TO), and anti-CD59 monoclonal antibodies (MoAb). TO was introduced to gate reticulocytes and anti-CD59 MoAb were used to identify glycosylphosphatidylinositol (GPI)-deficient cells.

Cells from healthy individuals were only CD59 positive. However, in all PNH patients, CD59-antigen expression could be divided into 3 types: type I cells (CD59 normally positive), type II cells (CD59 partly positive) and type III cells (CD59 negative). The majority of reticulocytes belonged to type III cells, GPI-deficient cells (61.0%). In addition, the percentage of affected reticulocytes was higher than that of erythrocytes.

Analyzing PNH reticulocytes was important, because most patients had elevated numbers of reticulocytes, which represent more closely the recent erythroid output of BM. However, circulating mature erythrocytes were subject to complement-mediated intravascular lysis. Therefore, the percentage of abnormal erythrocytes may not accurately reflect the proliferation rate of normal and abnormal erythroid progenitor cells. Thus, affected reticulocytes could be a more reliable indicator for the diagnosis of PNH than mature erythrocytes.