Induction and maintenance of allergen-specific FOXP3+ Treg cells in human tonsils as potential first-line organs of oral tolerance.

BACKGROUND: Tonsils are strategically located in the gateway of both alimentary and respiratory tracts representing the first contact point of food and aeroallergens with the immune system. Tonsillectomy removes only the palatine tonsils and sometimes adenoids. Lingual tonsil is anatomically big and remains lifelong intact. OBJECTIVE: The aim of this study was to demonstrate cellular and molecular mechanisms of oral tolerance induction to food and aeroallergens in human tonsils. METHODS: Tonsil allergen-specific FOXP3(+) regulatory T (Treg) cells, plasmacytoid dendritic cells (pDCs), and myeloid dendritic cells were characterized by flow cytometry and suppressive assays. Intracellular staining, [(3)H]-thymidine incorporation, and carboxy-fluorescein succinimidyl ester dilution experiments were performed. Tonsil biopsies were analyzed by confocal microscopy. RESULTS: CD4(+)FOXP3(+) Treg cells and pDCs constitute important T- and dendritic cell-compartments in palatine and lingual tonsils. Tonsil pDCs have the ability to generate functional CD4(+)CD25(+)CD127(-)FOXP3(+) Treg cells with suppressive property from naive T cells. CD4(+)FOXP3(+) Treg cells proliferate and colocalize with pDCs in vivo in T-cell areas of lingual and palatine tonsils. Tonsil T cells did not proliferate to common food and aeroallergens. Depletion of FOXP3(+) Treg cells enables the allergen-induced proliferation of tonsil T cells, indicating an active role of Treg cells in allergen-specific T-cell unresponsiveness. High numbers of major birch pollen allergen, Bet v 1-specific CD4(+)FOXP3(+) Treg cells, are identified in human tonsils compared with peripheral blood. A positive correlation between the percentages of FOXP3(+) Treg cells and pDCs is observed in tonsils from nonatopic individuals. CONCLUSION: Functional allergen-specific Treg cells are identified both in lingual and in palatine tonsils.

Unique phenotype of human tonsillar and in vitro-induced FOXP3+CD8+ T cells.

Forkhead box p3 (FOXP3) is known to program the acquisition of suppressive capacities in CD4(+) regulatory T cells (Treg), whereas its role in CD8(+) T cells is unknown. The current study investigates whether FOXP3 also acts as a Treg master switch in peripheral blood and tonsillar CD8(+) T cells. Single-cell analyses reveal the existence of a FOXP3(+)CD8(+) population in human tonsils, whereas FOXP3(+)CD8(+) T cells are rarely detected in peripheral blood. Tonsillar FOXP3(+)CD8(+) T cells exhibit a Treg phenotype with high CTLA-4 and CD45RO and low CD127 and CD69 expression. Interestingly, the tonsillar FOXP3(+)CD8(+) T cells are mostly CD25(negative) and some cells also express the proinflammatory cytokines TNF-alpha, IFN-gamma, or IL-17A. Particularly, IL-17A-expressing cells are present among FOXP3(+)CD8(+) T cells. Even though FOXP3 expression is at the detection limit in peripheral blood CD8(+) T cells ex vivo, it can be induced in vitro in naive CD8(+) T cells by polyclonal stimulation. The induced FOXP3(+)CD8(+) T cells are predominantly CD25(high) and CD28(high) and similar to tonsillar cells, they produce high levels of TNF-alpha, IFN-gamma, and granzyme B. However, IL-4 expression is mutually exclusive and IL-17A expression is not detectable. These FOXP3(+)CD8(+) T cells suppress the proliferation of CD4(+) T cells in cocultures, while showing no direct cytotoxic activity. In conclusion, the current study characterizes FOXP3-expressing CD8(+) T cells from human tonsils and shows that in vitro activation leads to FOXP3 expression in CD8(+) T cells and gain of suppressive activity.