Immunohistochemical Characterization of the Human Sublingual Mucosa

The sublingual locus has recently received great attention as a delivery site for various immunotherapies, including those that induce allergen-specific tolerance, and for vaccines that generate protective immunity. To further understand the immune functions of the human sublingual mucosa, we characterized the distribution of various immunocytes therein by immunohistochemistry. We identified professional antigen presenting cells (APCs), including Langerhans cells (LCs) and macrophages. $CD1a^+$ and $langerin^+$ LCs were further found to be distributed in the basal and supra-basal layers of the epithelium, and macrophages were identified in the lamina propria. HLA-$DR^+$ cells were observed in both the epithelium and the lamina propria, which mirrors the tissue distribution of LCs and macrophages within these tissues. $CD3^+$, $CD4^+$, and $CD8^+$ T cells were found to be distributed along the basal layer of the epithelium and also in the lamina propria. Although B cells, plasma cells, and $Foxp3^+$ regulatory T cells (Tregs) were only occasionally observed in the human sublingual mucosa in the absence of inflammation, they did show enrichment at inflammatory sites. Hence, we have further elucidated the immune cell component distribution in human sublingual mucosa.