Single-cell transcriptome analysis of human skin identifies novel fibroblast subpopulation and enrichment of immune subsets in atopic dermatitis

Background: Atopic dermatitis (AD) is a prevalent inflammatory skin disease with a complex pathogenesis involving immune cell and epidermal abnormalities. Despite whole tissue biopsy studies that have advanced the mechanistic understanding of AD, single cell based molecular alterations are largely unknown. Objective: Our aims were to construct a detailed, high-resolution atlas of cell populations and assess variability in cell composition and cell-specific gene expression in the skin of patients with AD versus in controls. Methods: We performed single-cell RNA sequencing on skin biopsy specimens from 5 patients with AD (4 lesional samples and 5 nonlesional samples) and 7 healthy control subjects, using 10x Genomics. Results: We created transcriptomic profiles for 39,042 AD (lesional and nonlesional) and healthy skin cells. Fibroblasts demonstrated a novel COL6A5(+)COL18A1(+) subpopulation that was unique to lesional AD and expressed CCL2 and CCL19 cytokines. A corresponding LAMP3(+) dendritic cell (DC) population that expressed the CCL19 receptor CCR7 was also unique to AD lesions, illustrating a potential role for fibroblast signaling to immune cells. The lesional AD samples were characterized by expansion of inflammatory DCs (CD1A(+) FCER1A(+)) and tissue-resident memory T cells (CD69(+)CD103(+)). The frequencies of type 2 (IL1(3+))/type 22 (IL22(+)) T cells were higher than those of type 1 (IFNG(+)) in lesional AD, whereas this ratio was slightly diminished in nonlesional AD and further diminished in controls. Conclusion: AD lesions were characterized by expanded type 2/type 22 T cells and inflammatory DCs, and by a unique inflammatory fibroblast that may interact with immune cells to regulate lymphoid cell organization and type 2 inflammation.