Single Cell Analysis Reveals Dynamic Changes of Distinct Cell Populations in Human Nickel Allergy

Nickel specifically activated distinct populations of endothelial cells, suprabasal keratinocytes, fibroblasts, and CCR7⁺ dendritic cells, co-expressing the TLR4-interacting proteogylcan DCN and CCR7 ligand CCL21 within 8 h. Skin-resident T cells were not involved in the early hypersensitivity response, as their gene expression remained unaltered 8 h after nickel exposure. However, substantial changes in the cutaneous T cell compartments occurred after 72 h, with massive infiltration of KLF2⁺ central memory T cells being a recurrent feature of both nickel-sensitized patients and individuals allergic to the glucocorticoid contact allergen budesonide.