Rapid allergen‐induced interleukin‐17 and interferon‐γ secretion by skin‐resident memory CD8 ⁺ T cells

Summary Background Skin‐resident memory T (T RM ) cells are associated with immunological memory in the skin. Whether immunological memory responses to allergens in the skin are solely localized to previously allergen‐exposed sites or are present globally in the skin is not clear. Furthermore, the mechanisms whereby T RM cells induce rapid recall responses need further investigation. Objectives To study whether contact allergens induce local and/or global memory, and to determine the mechanisms involved in memory responses in the skin. Methods To address these questions, we analysed responses to contact allergens in mice and humans sensitized to 2,4‐dinitrofluorobenzene and nickel, respectively. Results Challenge responses in both mice and humans were dramatically increased at sites previously exposed to allergens as compared with previously unexposed sites. Importantly, the magnitude of the challenge response correlated with the epidermal accumulation of interleukin (IL)‐17A‐producing and interferon (IFN)‐γ‐producing T RM cells. Moreover, IL‐17A and IFN‐γ enhanced allergen‐induced IL‐1β production in keratinocytes. Conclusions We show that sensitization with contact allergens induces a strong, long‐lasting local memory and a weaker, temporary global immunological memory response to the allergen that is mediated by IL‐17A‐producing and IFN‐γ‐producing CD8 + T RM cells.