Immunocytochemical and enzymecytochemical studies on the intracellular transport mechanism of secretory immunoglobulin A and lactoferrin in human salivary glands.

The intracellular transport mechanism of secretory immunoglobulin A (sIgA) has been immunocytochemically defined in human submandibular glands. To examine the properties of the intracytoplasmic vesicles which contain IgA, the enzyme labeled antibody method for SC and IgA and Novikoff's method for acid phosphatase (ACPase) activity were employed on the same sections. The intracytoplasmic vesicles containing IgA and SC in the serous acinar cells were free of ACPase activity and were thus distinguishable from lysosomes. Neither IgA nor SC was localized in the secretory granules. Lactoferrin was localized in the secretory granules and glandular lumen of the serous acinar cells, but not in the cytoplasmic vesicles, which were also free of ACPase activity. These findings suggests that the transport of sIgA was performed by intracytoplasmic vesicles and that lactoferrin is discharged from secretory granules into the lumen and finally makes a "rendezvous" with sIgA in the lumen of acinar cells.