Taste Papillae-associated Salivary Gland Ducts Contribute to Immune Surveillance

The lingual surface is composed of a tough epithelium that affords effective protection from the resident and food-borne microbiota. The circumvallate taste papillae (CVP) in the back of the tongue are associated with underlying minor salivary glands called von Ebner's gland (VEG) that drains its secretions into the trenches of the papillae. The taste buds are exposed to the lingual surface through taste pores, to enable interaction with tastants. These openings may be exploited by pathogens for infection. Mucosa-associated lymphoid tissue (MALT) such as those in the gut epithelium, tonsils and lachrymal and salivary ducts possess specialized cells called microfold (M) cells that transport luminal microbes and present them to underlying immune cells, which then initiate an appropriate immune response. Our previous work indicated that type II taste cells might mediate similar immune surveillance akin to M cells and that CVP is patrolled by large population of immune cells. Using single cell RNASeq (scRNASeq) of CVP, we discovered that the duct cells of the VEG strongly express markers for M cells. The ducts were capable of transcytosing fluorescently labelled E. coli and fluorescent nanobeads, which are then taken up by underlying immune cells. We propose that taste and duct cell-mediated immune surveillance might be crucial for preventing infection of taste papillae and for maintaining taste function, and conversely, this pathway might be hijacked by microbes for infection.