A new immunoenzyme tracer for immunohistology: peroxidase-labeled protein A. Its application for determination of antinuclear antibodies.

Protein A from Staphylococcus aureus, a cell wall protein with high affinity binding properties for IgG-type antibodies, has been labeled with peroxidase to form a stable immunohistological tracer molecule of relatively low molecular weight. It has been used for demonstration and titration of antinuclear antibodies in SLE sera on mouse liver sections in an indirect technique. The findings were consistent with those obtained by immunofluorescence and by staining with peroxidase-coupled anti-IgG. In contrast to immunofluorescence, the stained sections could be mounted and stored for documentation. In comparison, unspecific tissue adsorption and staining could be minimized by addition of glucose, galactose, and mannose as well as bovine serum albumine to the buffer containing Protein A-peroxidase.