Abstract
The antigenic substrate of the antiperinuclear factor (APF) in human buccal mucosa cells was studied by light microscopy, cytochemistry, and the immunofluorescence technique (IFT). The cytoplasmic granules against which the APF is directed stained basophilic in light-microscopical staining techniques. The granules did not show a positive reaction product by techniques in which special chemical components are stained, and no activity of lysosomal enzymes could be identified. The use of autoantibodies and other antisera directed to distinct tissues, components, or macromolecules did not resolve the character of the antigenic granules. In addition it was shown that human vaginal epithelial cells and cryostat sections of human and rabbit buccal and oesophageal mucosa incubated with APF-positive sera showed the same fluorescent granules in the IFT as human buccal mucosa cells. Cryostat sections of rabbit buccal and oesophageal mucosa were tested as an alternative substrate in the APF test. Since the specificity as well as the sensitivity decreased when these sections were used as a substrate, they are not suitable for diagnostic purposes.