Abstract—Alopecia Areata (AA) is an autoimmune disease resulting from a breach in the immune privilege of the hair follicles. To gain insights into the mechanism, we focused on the interactions between cells in the hair follicles. Dermal Papilla (DP) cells are especially essential for developing hair follicles and maintaining the growth phase of the hair cycle. We used a single-cell RNA sequencing dataset of hair follicles to analyze the interaction of immune cells, primarily with DP cells. This dataset was obtained from a patient with AA. To identify cell types that interact with DP cells and contribute to AA, we performed clustering of fibroblasts and T cells to identify DP and T cell subtype populations. Through cell-cell communication analysis, we also identified DP as the most statistically frequent interacting cell type. In addition, we identified T cell subtypes that interact with papilla cells and ligand-receptor pairs. By integrating the results of these analyses, we inferred specific T cell subtypes that interact with DP cells and predicted novel ligand-receptor pairs that shorten the growth (anagen) phase of the hair cycle by causing inflammation in both follicular and DP cells. 
 

Keywords—cell-cell interaction analysis, single-cell RNA sequencing, dermal papilla, hair follicle, T cell, alopecia areata