Immunoelectron microscopy of Fc receptors on the surface of clinical isolates of streptococci.

The distribution of Fc receptors on the surface of clinical isolates of streptococci was examined by immunoelectron microscopy. A unique two-layered ferritin tagging was observed on the surface of isolate MS-4 (group A). The spacing between the layers (10-40 nm) was narrower than that of the layered protein A (30-70 nm) on Staphylococcus aureus. Labeling on the other isolates, IP-28 (group A) and ES-21L (group C), showed similar rough layers, but the labeling were clearly different in thickness and density. The labeling on isolate IP-28 was also similar to that on strain AR1 (group A), reported previously, while the labeling on ES-21L was similar to that on protein G producing strain G148 (group G) in thickness. However, it was obviously thinner than that on IP-28 and AR1. These results strongly suggest that there are at least three distribution patterns of Fc receptors on streptococci, and these are distinct from that of protein A.