Occurrence of Fc-Reacting Factor in Acid Extracts of <i>Streptococcus pyogenes </i>and Its Relationship to M Protein

Abstract

The Fc-reacting factor (FcRF) of streptococci was studied by means of its hot-acid extraction from streptococcus cells and hemagglutination of sensitized erythrocytes. This hemagglutination could be inhibited by rabbit IgG and the Fc fragment of IgG. There was no correlation between the occurrence of FcRF and M protein. The FcRF was found more frequently in freshly isolated than in old strains. The FcRF could be separated from M protein by gel filtration. The molecular weight of FcRF was estimated roughly at 100,000 daltons.