Quantitation of complement sensitivity and demonstration that paroxysmal nocturnal hemoglobinuria (PNH) erythrocytes are a mosaic. Rosse and Dacie developed the complement lysis sensitivity assay to quantify the complement sensitivity of PNH erythrocytes. In the case shown, both complement-sensitive and complement-insensitive populations were identified. RBCs from a patient with PNH (closed circles) and from a normal volunteer (open triangles) were incubated with antibody in excess and incremental (limiting) dilutions of serum as the complement source. Subsequently, hemolysis was quantified. The inflection point of the curve that marks the end of lysis of the complement-sensitive cells and the beginning of lysis of the complement-insensitive cells is indicated by the solid lines. The dashed lines mark the dilution of serum required to produce 50% lysis of normal RBCs and of the complement-sensitive and complement-insensitive PNH cells. These studies demonstrated that PNH erythrocytes are approximately 25 times more sensitive to complement-mediated lysis than normal erythrocytes and that the peripheral blood of patients with PNH is a mosaic of normal and abnormal cells.
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