Diverse roles of dendritic cell and regulatory T cell crosstalk in controlling health and disease.

Dendritic cells (DCs) are specialized antigen-presenting cells for lymphocytes, including regulatory T (Treg) cells, a subset of CD4+ T cells expressing CD25 and Foxp3, a transcription factor. Treg cells maintain immunological self-tolerance in mice and humans, and suppress autoimmunity and other various immune responses such as tumor immunity, transplant rejection, allergy, responses to microbes, and inflammation. Treg-cell proliferation is controlled by antigen-presenting DCs. On the other hand, Treg cells suppress the function of DCs by restraining DC maturation. Therefore, the interaction between DCs and Treg cells, DC-Treg crosstalk, could contribute to controlling health and disease. We recently found that unique DC-Treg crosstalk plays a role in several conditions. First, Treg cells are expanded in ultraviolet B (UVB)-exposed skin by interacting with DCs, and the UVB-expanded Treg cells have a healing function. Second, manipulating DC-Treg crosstalk can induce effective acquired immune responses against severe acute respiratory syndrome coronavirus 2 antigens without adjuvants. Third, Treg cells with a special feature interact with DCs in the tumor microenvironment of human head and neck cancer, which may contribute to the prognosis. Understanding the underlying mechanisms of DC-Treg crosstalk may provide a novel strategy to control health and disease.