Protein A-peroxidase: a valluable tool for the localization of antigens.

Protein A of Staphylococcus aureus has been conjugated to horseradish peroxidase and used in an indirect immunolabeling technique to visualize membrane and viral antigens. The same Protein A-peroxidase conjugate was used with antisera from five different species. Using this indirect test, membrane markers for T and B lymphocytes were labeled with a greater specificity than when peroxidase conjugated anti-immunoglobulin was used in the second step. Viral antigens on cells infected with measles, vesicular stomatitis, herpes or visna virus, respectively, were also stained in the protein A-peroxidase indirect test with a greater specificity than indirect method using anti-immunoglobulin. Paired preparations were examined in the light and electron microscope. Ultrastructural analysis showed that the protein A-peroxidase conjugate penetrated well through fixed viral membranes and resulted in fine resolution of antigenic sites.