Cutaneous Neuroimmunology: Lessons from the Hair Follicle

The document explored the hair follicle as a model for studying cutaneous neuroimmunology, focusing on how stress-response systems integrate with the skin's immune system and epithelial-mesenchymal interactions during hair growth. It was found that skin mast cells, which are central to inflammation and tissue remodeling, also regulate hair growth in mice. Endogenous mast cell secretagogues, such as ACTH and neuropeptides like SP, were identified as potent hair growth modulators. The study highlighted the role of stress-associated neuropeptides, such as SP and NGF, in inhibiting hair growth by activating mast cells and promoting inflammation. Additionally, the neurohormone CRH was shown to inhibit hair growth and activate a peripheral equivalent of the hypothalamic-pituitary-adrenal axis in human scalp hair follicles. The research also demonstrated that α-MSH could suppress MHC class I expression, restoring immune privilege in hair bulbs, while SP upregulated MHC class I expression, compromising immune privilege. Furthermore, vanilloids like capsaicin were found to modulate hair growth by stimulating vanilloid receptors in the follicle epithelium. Overall, the hair follicle served as a valuable model for understanding the interactions between the nervous system, endocrine signaling, and the immune system in adapting skin functions to environmental changes.