Representative flow cytometric patterns of membrane CD59/MACIF and/or DAF expression by normal or PNH erythrocytes and erythroblasts. In 2-color analysis, 4 regions (shown by the lines) were set using the flow cytometric data of negative controls examined at the same time. Expression of CD59/MACIF and DAF by PNH erythrocytes and erythroblasts was defined as negative, intermediate, or positive based on the intensity of fluorescein isothiocyanate fluorescence (FL1) and phycoerythrin fluorescence (FL2). Erythrocytes of all 31 volunteers and erythroblasts of four volunteers consisted of a single population showing high-level expression of both proteins. In 1-color analysis of CD59/MACIF or DAF expression by PNH erythrocytes and erythroblasts, 3 fractions (negative, intermediate, and positive) were also detected. In contrast, normal erythrocytes and erythroblasts showed a single population with high-level expression. Thin lines show negative controls, thick lines show tested subjects, and vertical axes represent cell counts. A, normal volunteer; B, case 3; C, case 7; D, case 8; E, case 9.