Comparison of type III Fc receptors associated with group C and group G streptococci.

The type III Fc receptors present on or secreted by a series of group C and G streptococcal strains were studied. All strains capable of binding radiolabeled human IgG were shown to do so via an antigenically related Fc receptor. Treatment of any of the bacterial strains with papain or trypsin resulted in solubilization of Fc receptor activity. The pattern of Fc receptor activity recovered following enzyme treatment was not uniform. Differences were observed both between group C and G strains as well as within group C and G strains. Analysis of secreted Fc receptors indicated the presence of five molecular forms of Fc receptor. Each form was present at some level in the supernatant of every group C and G strain studied. The relative concn of each form of receptor secreted varied from strain to strain. The Fc receptor activity secreted by each strain demonstrated a similar affinity for the Fc region of human IgG and all were antigenically related. These results suggest that there is a family of closely related Fc receptors associated with group C and G streptococcal strains.