The regulatory B cell–mediated peripheral tolerance maintained by mast cell IL-5 suppresses oxazolone-induced contact hypersensitivity

The function of regulatory immune cells in peripheral tissues is crucial to the onset and severity of various diseases. Interleukin-10 (IL-10)–producing regulatory B (IL-10(+) B(reg)) cells are known to suppress various inflammatory diseases. However, evidence for the mechanism by which IL-10(+) B(reg) cells are generated and maintained is still very limited. Here, we found that IL-10(+) B(reg) cells suppress the activation of IL-13–producing type 2 innate lymphoid cells (IL-13(+) ILC2s) in an IL-10–dependent manner in mice with oxazolone-induced severe contact hypersensitivity (CHS). Mast cell (MC) IL-5 was important for maintaining the population of IL-10(+) B(reg) cells in peripheral lymphoid tissues. Overall, these results uncover a previously unknown mechanism of MCs as a type of immunoregulatory cell and elucidate the cross-talk among MCs, IL-10(+) B(reg) cells, and IL-13(+) ILC2s in CHS.