The Properdin System and Immunity . Iv . the Hemolysis of Erythrocytes Frompatients with Paroxysmal

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare chronic hemolytic anemia characterized by an acquired defect of the erythrocyte which renders it susceptible to hemolysis by normal human serum. Previous reports have indicated that magnesium and factors resembling the components of complement are required for the hemolysis in vitro of PNH erythrocytes by normal serum (1, 2). Recently a naturally occurring serum protein, properdin, has been described which requires magnesium and complement for its activity in vitro (3). Thus, properdin, magnesium, and complement have been termed the properdin system, which participates in the lysis of certain bacteria and the inhibition of certain viruses (4, 5). The resemblance between the factors required for PNH hemolysis and the constituents of the properdin system prompted this study on the role of the properdin system in the hemolysis of PNH erythrocytes.