Summary Staphylococcal agglutinogen was extracted from undigested cell walls and purified through carboxymethyl (CM)-cellulose column chroma tography and molecular sieving by Sephadex G-75. The sedimentation patterns of ultracentrifugation showed a high degree of homogeneity of the purified agglutinogen. The sedimentation constant is 1.6 S, the diffusion constant is 11.6 × 10-7 cm2/sec, and the molecular weight is 13,200. It showed single line precipitation reactions with human and rabbit antisera in agar gel diffusion and immunoelectrophoresis. From the nitrogen content, ultraviolet absorption, and sensitivity against digestion by proteolytic enzymes, it was shown that the agglutinogen is a protein. Jensen's antigen A contains the agglutinogen.

Summary A protein agglutinogen common to the internationally recognized serotypes of Staphylococcus aureus is described. Sera of all human subjects studied, healthy or infected, possess a high and fairly uniform level of antibodies against this agglutinogen. The agglutinin is concentrated in commercial human γ-globulin and is deficient in the blood of agammaglobulinemic children. No immunizing agent has been found which will regularly increase agglutination titers in man to a significant degree, although some increase has been induced in rabbits. Serum absorbed with the pure protein agglutinogen shows decreased agglutination titer against all serotypes but is not deprived of its phagocytosis promoting power.