Immune Cell Regulation of the Hair Cycle

The review article by Etienne CE Wang and Claire A. Higgins, published on February 5, 2020, examined the role of immune cells in the regulation of the mammalian hair cycle and their relevance to human hair cycling disorders. The authors noted that immune cells, such as macrophages, T cells, and mast cells, are involved in the different phases of the hair cycle and may impact hair growth and conditions like alopecia areata (AA) and androgenetic alopecia (AGA). They discussed the differences between spontaneous and induced hair cycling, the role of immune cells in hair shedding and the kenogen phase, and the potential of JAK inhibitors in treating AA. The review also mentioned the possibility of using treatments like platelet-rich plasma to rejuvenate miniaturized follicles in AGA. The authors emphasized the complexity of studying the human hair cycle and the need for better understanding to improve treatments for hair loss disorders. They suggested that single-cell transcriptomics could help identify immune cell subsets in human skin and reveal new therapeutic targets for hair loss, while also noting that side effects from biologic and immunotherapy treatments could provide insights into relevant biological pathways. The paper concluded with a call for systematic human studies to develop new treatments for hair loss, acknowledging the limitations of current knowledge based on mouse models.