Architecture of associations of minor salivary gland ducts and lymphoid follicles in Macaca fascicularis. An ultrastructural study.

Previous light-microscopic and ultra-immunohistochemical tracer studies revealed the existence of an independent local immune response of the simian oral mucosa. This local response is attributed to the presence of minor salivary gland (MSG) duct-related lymphoid tissue. Semithin sections from a total of 263 Epon-embedded tissue blocks from the labial and buccal mucosae of seven monkeys, Macaca fascicularis, were analysed light-microscopically, and 10 suitable MSG duct/follicle assemblies were investigated ultrastructurally. These duct/follicle assemblies include follicular and parafollicular compartments with distinct fine-structural elements. The follicular area or germinal centre contains numerous small and large lymphoid cells, mitotic figures, plasmablasts, macrophages, and cells resembling the follicular dendritic cells with distinct desmosomal junctions. The parafollicular area, which includes the heavily infiltrated duct wall, contains numerous small lymphocytes, T-lymphoblasts, plasma cells and reticular cells resembling fibroblasts. A distinct feature of this compartment is the presence of high endothelial venules (HEV). The presence of HEV and numerous blast cells, resembling blast-forming T-lymphocytes activated in vitro, in a specific area of the duct/follicle assembly strongly suggests that this area is structurally and physiologically identical to the thymus-dependent area of other lymphoid tissues. In other words, the duct/follicle assemblies of simian MSG contain the various specific fine-structural elements that are suitable for antigen recognition and processing. These elements are distributed in discrete compartments comparable to the B- and T-cell areas of "classical" lymphoid tissue.