Mucosal dendritic cells in allergy and immunotherapy.

The oral epithelium contains oral mucosal Langerhans cells (oLCs) that constitutively express the high-affinity IgE-receptor FcεRI, the lipopolysaccharide receptor CD14 and toll-like receptor (TLR)4. The distribution of oLCs profoundly differs at distinct oral mucosal sites, with higher numbers of oLCs detectable in the vestibulum compared with the sublingual region. The oLC response to activation of TLR4 and FcεRI and to binding of allergen suggests that these cells are involved in the maintenance of tolerance towards bacterial components and allergens. Thus, oLCs are important targets for allergens and adjuvants during sublingual immunotherapy, and characterizing them is crucial for improving allergen-specific immunotherapy.