Regulatory T Cells Influence Hair Follicle Cycle and Stem Cell Activation

The study by Ali et al. demonstrated that regulatory T (Treg) cells, which are typically known for suppressing inflammation, play a crucial role in regulating the hair follicle cycle by influencing hair follicle stem cells (HFSCs). The researchers found that Treg cells were more abundant during the resting phase of hair growth (telogen) and had an activated phenotype. In experiments with mice, those with transiently depleted Treg cells showed impaired hair regrowth after depilation, indicating that Treg cells are essential for the transition from telogen to the growth phase (anagen) and for hair follicle regeneration. Further analysis revealed that Treg cells promote HFSC proliferation and differentiation, a process not related to their anti-inflammatory functions. This was supported by the finding that jagged 1, a gene involved in Notch signaling, was differentially expressed in Treg cells and necessary for HFSC activation, as mice with jagged 1-deficient Treg cells had reduced hair follicle regeneration. Thus, the study concluded that skin-resident Treg cells have a novel, tissue-specific function in inducing Notch-dependent HFSC proliferation and differentiation, which is vital for the hair follicle cycle.