Minor salivary gland duct-associated lymphoid tissue (DALT) in monkeys changes with age

The duct-associated lymphoid tissue (DALT) of minor salivary glands (MSG) is accessible to oral antigens by retrograde passage. DALT responds immunologically to such purely local and duct-derived antigenic stimuli. This study addressed the question as to whether DALT, like other mammalian lymphoid tissues, would change with age. Labial and buccal mucosae of eight Macaca fascicularis animals of known age were processed for light microscopy by Epon embedding. Sections of approximately 1-2 microns thick were prepared, and a total of 144, more or less equidistant, labial and 63 buccal sections were selected and analyzed for various tissue components, by means of morphometric point-counting. The raw data were transformed into stereological parameters. The results showed that DALT and interacinar plasma cells are totally absent in the newborn monkey. They begin to appear early in life and reach a maximum volume density by one year of age. With further increasing age, the DALT volume showed a sharp decline, followed by a plateauing from year 3 onward, while the plasma cell concentration remained stable. This change was more pronounced in the labial mucosa. These observations on the age-related changes of simian DALT are suggestive of its antigen-induced and antigen-dependent nature. DALT, being part of the gut-associated lymphoid tissue, may play a substantial role in the local immuno-surveillance of the oral cavity.