A detailed characterization of oral antigen-presenting cells is critical to improve second-generation sublingual allergy vaccines.

To characterize oral dendritic cells (DCs) within lingual and buccal tissues from BALB/c mice with respect to their surface phenotype, distribution, and capacity to polarize CD4⁺ T-cell responses.

In situ analysis of oral DCs was performed by immunohistology. Purified DCs were tested in vitro for their capacity to capture, process, and present the ovalbumin antigen to naive CD4⁺ T cells. In vivo priming of ovalbumin-specific T cells adoptively transferred to BALB/c mice was analyzed by cytofluorometry in cervical lymph nodes after sublingual administration of mucoadhesive ovalbumin.

Three subsets of oral DCs with a distinct tissue distribution were identified: (1) a minor subset of CD207⁺ Langerhans cells located in the mucosa itself, (2) a major subpopulation of CD11b⁺CD11c⁻ and CD11b⁺CD11c⁺ myeloid DCs at the mucosal/submucosal interface, and (3) B220⁺120G8⁺ plasmacytoid DCs found in submucosal tissues. Purified myeloid and plasmacytoid oral DCs capture and process the antigen efficiently and are programmed to elicit IFN-γ and/or IL-10 production together with a suppressive function in naive CD4⁺ T cells. Targeting the ovalbumin antigen to oral DCs in vivo by using mucoadhesive particles establishes tolerance in the absence of cell depletion through the stimulation of IFN-γ and IL-10–producing CD4⁺ regulatory T cells in cervical lymph nodes.

The oral immune system is composed of various subsets of tolerogenic DCs organized in a compartmentalized manner and programmed to induce T_H1/regulatory T-cell responses.