Immunohistochemistry of saline-extracted human glandular tissue revealed that secretory epithelial cells contain membrane-associated IgA and secretory component (SC). Free SC alone was demonstrated intracellularly in the Golgi region whereas both free and IgA-complexed SC were detected in the cell membranes and in the apical portion of the cytoplasm. The findings support a tentative model for selective epithelial immunoglobulin transmission. It is proposed that SC acts as a specific surface receptor for dimeric IgA, and that the formed complexes become mobilized and at least partially stabilized in the cell membrane. They subsequently enter the gland lumen via the epithelial cell cytoplasm outside the Golgi apparatus, and perhaps, to some extent, directly from the cell membrane.
This work was supported by the Norwegian Research Council for Science and the Humanities, Grosserer N. A. Stangs Legat, and Anders Jahres Fond. The cost of the color plate was in part kindly defrayed by the following companies: A/S Kabi, Norske Hoechst A/S, and Einar D. Fineide A/S.