Demonstration and assaying of IgG antibodies in tissues and on cells by labeled staphylococcal protein A.

Staphylococcal protein A (SpA) labeled with FITC was used to detect IgG antibodies to tissue and cell surface antigens. Radioiodinated SpA was employed in a radioimmuno technique to assay IgG antibodies which had reacted with cell membrane antigens. Red blood cells coated with SpA were used as an indicator system in the mixed haemadsorption technique to detect IgG antibodies on tissue culture cells. The results showed that SpA was highly specific in the various systems tested, although it was not as sensitive in the immunofluorescence test as FITC anti-IgG. It was confirmed that SpA reacts with IgG antibodies of human, monkey, rabbit, sheep and mice origin. The reactivity with human and monkey IgG was stronger than with IgG of the other species. We consider labeled SpA as an alternative to monospecific anti-IgG for detection and assaying of IgG antibodies to tissue and cell surface antigens.