Visualization of the binding of IgG myeloma proteins to some group A streptococci.

The interaction between streptococci and human IgG, which does not involve the antibody combining sites, was visualized in the electron microscope by the use of human IgG myeloma proteins and ferritin labelled rabbit anti-human IgG antibodies. The streptococci were allowed to react with human IgG myeloma proteins and the human IgG was then marked by addition of ferritin labelled rabbit anti-human IgG antibodies; sections of streptocci studied in electron microscopy showed localization of the ferritin on the surface of the cell wall of all the streptococci of type M 1, M 3, M 12 and M 56 studied. Similar results were obtained if the ferritin labelled rabbit anti-human IgG antibodies alone were allowed to react with the streptococci. The uptake of ferritin labelled rabbit anti-human IgG antibodies could be inhibited by addition of normal rabbit serum.