Detection of small populations of CD59-deficient erythrocytes in patients with aplastic anemia or myelodysplastic syndrome and normal individuals

To detect a small population of blood cells with a deficiency of glycosyl p hosphatidylinositol (GPI)-anchored protein, we evaluated the expression of CD59 by flow cytometry on one million erythrocytes, which is about 100 time s more than the number of erythrocytes tested by our standard immunoassay, Blood samples from healthy volunteers, patients with aplastic anemia (AA), and patients with myelodysplastic syndrome (MDS), who all showed no detecta ble GPI deficiency by the standard assay, were investigated. The numbers of CDS9-deficient erythrocytes were 5 to 145/10(6) erythrocytes in the health y volunteers (mean 29.2), and one of the volunteers had an increase in the deficient cells exceeding the mean + 3 SD (141.7), a normal limit. A CD59-d eficient population was detected in 6 of the 21 (28.6%) patients with AA an d 5 of the 18 (27.8%) patients with MDS, The new assay was performed again in 5 of these 11 patients and the normal individual who had the CD59-defici ent populations at 5 and 12 months after the initial study. The number of d eficient cells gradually increased in 1 patient with MDS (from 511 to 2892/ 10(6) erythrocytes), while the numbers of the other 4 patients showed a ten dency to decline, although the deficient populations were repeatedly detect ed on most of the occasions. Changes in the number of the deficient cells w ere also seen in the healthy volunteer, but they were rather rapid; the num bers changed from 145 to 5661 and then to 18/10(6) erythrocytes within 3 mo nths. The CD59 assay used in this study is easy to perform and enabled us t o detect less than 1% GPI-deficient cells. (C) 2000 Academic Press.