Basophil-derived amphiregulin is essential for UVB irradiation-induced immune suppression.

UVB irradiation (290–320 nm) is used to treat skin diseases like psoriasis and atopic dermatitis, and is known to suppress contact hypersensitivity (CHS) reactions in mouse models. Regulatory T cells (T reg cells) have been shown to be responsible for this UVB-induced suppression of CHS. The epidermal growth factor (EGF)-like growth factor amphiregulin (AREG) engages EGFR on T reg cells and, in different disease models, it was shown that mast cell–derived AREG is essential for optimal T reg cell function in vivo . Here we determined whether AREG has a role in UVB-induced, T reg cell–mediated suppression of CHS reactions in the skin. Our data show that AREG is essential for UVB-induced CHS suppression. In contrast to the general assumption, however, mast cells were dispensable for UVB-induced immune suppression, whereas basophil-derived AREG was essential. These data reveal, to our knowledge, a previously unreported function for basophils in the homeostasis of immune responses in the skin. Basophils thus fulfill a dual function: they contribute to the initiation of effective type 2 immune responses and, by enhancing the suppressive capacity of local T reg cell populations, also to local immune regulation in the skin.