Oral CD103−CD11b+ classical dendritic cells present sublingual antigen and induce Foxp3+ regulatory T cells in draining lymph nodes

Sublingual immunotherapy (SLIT) is a safe and efficient treatment for type 1 allergies; however, the underlying immunological mechanisms, particularly the phenotype of oral antigen-presenting cells (APCs) responsible for the induction of regulatory T (Treg) cells, remain unclear. We show here that the sublingual application of ovalbumin (OVA) induced antigen-specific Foxp3+ Treg cells in draining submandibular lymph nodes (ManLNs). Oral APCs were classified into macrophages, classical dendritic cells (cDCs), and Langerhans cells by flow cytometry. A major subset of oral cDCs with the CD103-CD11b+ phenotype showed retinoic acid (RA)-producing activity and converted naive CD4+ T cells to Foxp3+ Treg cells in a transforming growth factor-β- and RA-dependent manner in vitro. In the ManLNs, migratory CD103-CD11b+ cDCs also showed RA-producing activity. After the sublingual application of fluorescent OVA, fluorescence was detected in oral macrophages in tissues, followed by migratory CD103-CD11b+ cDCs in ManLNs and migratory CD103-CD11b+ cDCs were the main APCs responsible for the induction of sublingual antigen-specific Treg cells. The transfer of OVA-SLIT-induced Treg cells suppressed the OVA-induced hypersensitivity response. These results suggest that oral CD103-CD11b+ cDCs transport sublingual antigens to draining ManLNs and induce antigen-specific Foxp3+ Treg cells, and, thus, provide a rationale for developing cDC-based therapeutic approaches in SLIT.