Immune cells of the human peripheral taste system: Dominant dendritic cells and CD4 T cells
Taste loss or alterations can seriously impact health and quality of life due to the resulting negative influence on eating habits and nutrition. Infection and inflammation are thought to be some of the most common causes of taste perception disorders. Supporting this view, neuro-immune interactions in the peripheral gustatory system have been identified, underlying the importance of this tissue in mucosal immunity, but we have little understanding of how these interactions influence taste perception directly or indirectly. This limited understanding is evident by the lack of even a basic knowledge of the resident immune cell populations in or near taste tissues. The present study characterized the distribution and population of the major immune cells and their subsets in healthy human anterior, lingual, fungiform papillae (FP) using immunohistochemistry. Dendritic cells (DCs) were the predominant innate immune cells in this tissue, including four subtypes: CD11c^+ DCs, DC-SIGN+ immature DCs, CD83^+ mature DCs, and CD1a^+ DCs (Langerhans cells). While most DCs were localized beneath the lamina propria and only moderately in the epithelium, CD1a^+ Langerhans cells were exclusively present within the epithelium and not in sub-strata. A small number of macrophages were observed. T lymphocytes were present throughout the FP with CD4^+ T cells more prevalent than CD8^+ T cells. Very few CD19^+ B lymphocytes were detected. The results show that DCs, macrophages, and T lymphocytes are the constitutive guardians of human FP taste tissue, with DCs and CD4 T cells being dominant, while B lymphocytes are rare under normal, healthy conditions. These observations provide a basic anatomical foundation for the immune response in the healthy human tongue as a basis for subsequent disease-related studies, but none of the present data indicate that the immune cell populations identified are, in fact, altered in individuals with abnormal taste perception.