Ultrastructural localization of intracellular antigens by the use of protein A-gold complex

An immunocytochemical technique for the demonstration of intracellular antigens (secretory proteins) on thin sections is reported. Staphylococcal protein A which reacts with the Fc fragment of IgG molecules was labeled with colloidal gold as a marker. The antigenic sites were visualized on aldehyde-fixed and Epon-embedded tissue in a two step procedure. The specific antisera were applied to thin sections for binding to the antigens and then visualized by the protein A-gold complex. By using this technique different secretory proteins of the exocrine and endocrine pancreas were localized. The protein A-gold technique is proposed as a general method for visualization of antigenic sites on thin sections.