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Immunochemistry of the Streptococcal Group R Cell Wall Polysaccharide Antigen

^a Department of Microbiology, Northwestern University Medical School, Chicago, Illinois 60611

ABSTRACT

The group R streptococcal group antigen has been shown to be a polysaccharide located at the surface of the cell wall of the organism. The antigen was extracted from cell walls in 0.05 N HCl or 5% trichloracetic acid at 100 C, from whole cells at room temperature in 0.85% NaCl or 0.1 M acetate (pH 5.0), and by sonic oscillation. The antigen is largely destroyed when extracted from whole cells in 0.05 N HCl at 100 C. Acetate is recommended for routine extraction. The antigen extracted by sonic treatment was separated into six immunologically active fractions on diethylaminoethyl-Sephadex. The fractions were found to possess a common antigen which exhibited similar properties on immunodiffusion and immunoelectrophoresis. The purified antigen did not react with any other streptococcal group antisera. Adsorption of group R serum with the antigen removed all antibodies against whole cell antigen extracts of R cells. Chemical and enzymatic analysis of three fractions showed that the antigen was composed of D-glucose, D-galactose, rhamnose, and glucosamine. No significant quantities of phosphorus, glycerol, ribitol, or muramic acid were present. Significant inhibition of the quantitative precipitin determination by D-galactose and stachyose indicated that galactose in terminal alpha linkage was the immunodominant hexose in the antigen. D-Glucose and D-glucosamine possessed a partial inhibitory activity. N-acetyl-D-glucosamine and L-rhamnose did not produce significant inhibition. The results indicate that the R antigen is an immunologically specific structure which serves as a reliable means of identification of these streptococci as a serological group.

¹ Present address: LaRabida—University of Chicago Institute, Chicago, Ill. 60649.