An indirect immunofluorescence staining procedure for detection of human Fc gamma receptors on streptococci.

Fc gamma receptors on streptococci are usually revealed by hemagglutinating techniques (IgG coated red blood cells) or uptake of radiolabeled IgG. The results obtained with these methods are not always satisfactory. For this reason, we developed a technique involving indirect immunofluorescence staining. Bacterial smears were treated with human Fc gamma fragment and their binding to streptococcal Fc gamma receptors was revealed by a fluorescent F(ab')2 fragment of anti-human Fc gamma sheep antibodies purified on an IgG immunosorbent. These purified sheep F(ab')2 fragments did not contain any IgG nor Fc gamma as shown by SDS polyacrylamide gel electrophoresis. Under these conditions indirect immunofluorescence staining was a highly specific and sensitive method of detecting Fc gamma receptors on streptococci. Distribution of Fc gamma receptors was studied in 237 streptococcal strains of human origin belonging to groups A, B, C, D and G; these receptors were also looked for in 21 strains of alpha-hemolytic streptococci which did not possess the group carbohydrate and 12 strains of pneumococci. Fc gamma receptors were found only in group A, C and G streptococci, but all strains of these groups did not possess Fc gamma receptors.