Properties of Highly Purified Human Properdin

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Abstract
Summary: Partially purified human properdin was further purified by column chromatography on diethylaminoethyl (DEAE)-cellulose and carboxymethyl-Sephadex. The most highly purified preparation was electrophoretically and ultracentrifugally homogeneous. The diffusion coefficient D20,w was 2.2 × 10-7 cm2/sec; the sedimentation constant S20,w was 5.2 S; and the molecular weight was 223,000. Highly purified properdin formed a single characteristic line in the β-globulin region on immunoelectrophoresis with rabbit anti-properdin serum and failed to react with rabbit antisera to whole human serum, to γG-, γM- or γA- globulins, or to type K or L light chains of human immunoglobulins. Highly purified properdin retained the property of restoring activity to properdin-deficient serum in the zymosan assay, in the ability to cause lysis of erythrocytes from patients with paroxysmal nocturnal hemoglobinuria and in the killing of Shigella dysenteriae. Properdin activity in both biologic test systems correlated well with properdin activity as measured in the zymosan assay. Properdin did not restore bactericidal activity of serum specifically absorbed with homologous bacteria, but specific bactericidal antibody did not function in this system without properdin. Highly purified properdin neither combined with nor caused agglutination of zymosan. It was without effect on the hemolytic activity of whole complement, had little or no influence on the hemolytic activity of any purified component of complement tested, and was functionally and antigenically unrelated to such complement components. These data demonstrated the existence of properdin as a unique serum protein, distinct from known immunoglobulins or complement components, which participates in certain immunologic reactions of human serum.