Relevance of distinct skin-resident cell populations in human contact allergy

To identify the relevant cell types and signals mediating human nickel hypersensitivity, we used single-cell RNA sequencing of cells from a donor sensitized to nickel (but not chromium) who was epicutaneously exposed to either diluent or both metals for 8 or 72 hours. Our results suggest that nickel exposure specifically activates certain populations of endothelial cells, suprabasal keratinocytes, and CCR7+ dendritic cells within 8 hours, a response not observed with chromium exposure.

Skin resident T cells were not involved in the early hypersensitivity response as their gene expression remained unaltered 8 hours after nickel exposure. However, substantial changes in the cutaneous T cell compartments were observed after 72 hours of nickel exposure, including infiltration of SELL+ central memory T cells, effector Tc cells, TH cells, and Treg cells.