Detection of CD55- and CD59-Negative Immature Reticulocytes May Improves Sensitivity/Specificity to Identify a Minor Population of PNH-Type Cells in Patients with Myelodysplastic Syndrome/Aplastic Anemia

Paroxysmal nocturnal hemogloblinuria (PNH) is a hemolytic disease characterized by complement-sensitive red blood cells (RBC). Sometimes, a tiny amount of PNH-type, i.e., CD55- or CD59-negative, red blood cells as well as neutrophils can be detected in peripheral blood from patients with myelodysplastic syndrome (MDS)/ aplastic anemia (AA). It has been reported that the presence of PNH-type cells is correlated with a good response to immunosuppressive therapy foe these disease. However, the ratio of PNH-type RBCs to normal RBCs is always underestimated because PNH-type red blood cells have a shortened life span in the circulation, and there are some patients who have very low number of circulating granulocytes.

Peripheral blood was obtained from 37 patients with MDS or AA and 30 normal subjects. Mononuclear cells were then stained with antibodies against CD55, CD59, and CD71, and analyzed by a flowcytometer. Subsequently, CD55 and CD59-negative and CD71-positive reticulocytes, representing an immature fraction of reticulocytes, were identified. Sensitivity and specificity were compared for the detection of PNH-type immature reticulocytes with those evaluated by a PNH-type RBC- and granulocyte-detecting method.

All 30 normal subjects were negative when the cut-off value for CD55 and CD59-negative and CD71-positive reticulocytes was set at 0.008%. With this cut-off value, PNH-type immature reticulocytes were detected in 18 out of 37 MSA/AA patients. When the cut-off values for PNH-type RBCs and granulocytes were set at 0.005% and 0.01%, respectively, in accordance with the original report by Sugimori, et al, 16 and 18 cases among 37 MDS/AA patients were positive for PNH-type RBCs and granulocytes, respectively. All the 16 cases positive for PNH-type RBCs were also positive for PNH-type granulocytes and immature reticulocytes, while 2 cases negative for PNH-type RBCs were evaluated to be positive for both PNH-type granulocytes and immature reticulocytes. All the cases positive for granulocytes were also positive for immature reticulocytes, and vice versa. These observations indicate that the method to detect minor population of PNH-type immature reticulocytes is feasible and comparable with that to detect PNH-type granulocytes, and could be superior to the PNH-type RBC-detection method in terms of sensitivity, without reducing specificity. If the evaluation of PNH-type granulocytes is difficult, PNH-type immature reticulocytes may be a good alternative to be evaluated.

No relevant conflicts of interest to declare.