DEMONSTRATION AND ORGANIZATION OF DUCT-ASSOCIATED LYMPHOID-TISSUE (DALT) OF THE MAIN EXCRETORY DUCT IN THE MONKEY PAROTID-GLAND

Duct-associated lymphoid tissue (DALT) of the main excretory duct in t he monkey parotid gland was first demonstrated by Light microscopy and by transmission and scanning electron microscopy. The DALT included a follicular area, a parafollicular area and a specialized overlying ep ithelium with distinct fine-structural elements. There was usually a s olitary lymphoid follicle located in the subepithelial area near the o rifice of the parotid duct, The lymphoid follicles typically had a dis tinct germinal center, Numerous immune cells often infiltrated into th e epithelium overlying the lymphoid follicle. The superficial epitheli al cells of the DALT were larger and flatter than the ordinary duct ep ithelial cells, and had short irregular microvilli on their luminal su rface, They were also in close contact with immune cells such as dendr itic cells and lymphocytes. Goblet cells were rare in this area, In ad dition, bacteria, seen at the duct orifice, were sometimes taken up by the flattened epithelial cells near the orifice, Latex microspheres a dministrated as particulate antigens at the duct orifice were selectiv ely taken up by the flattened epithelial cells and also by the intraep ithelial dendritic cells of the DALT. These morphological findings sug gest that the epithelial cells of the DALT in parotid glands take up a ntigens from the duct lumen and transport them to adjacent immune cell s, and that the DALT in parotid glands may serve as one of the inducti ve sites in the common mucosal immune system.