The Human Hair Follicle: A Reservoir of CD40+ B7-Deficient Langerhans Cells That Repopulate Epidermis After UVB Exposure

The study from 1998 demonstrated that human hair follicles served as a critical reservoir for Langerhans cells, which repopulated the epidermis after UVB exposure. Following UVB irradiation, interfollicular epidermal Langerhans cells decreased significantly, but CD1a+ Langerhans cells were observed migrating from hair follicles to the epidermis within 48-96 hours. These migrating cells showed a deficiency in upregulating B7 costimulatory molecules, though they expressed CD40, indicating an intermediate maturation step. The findings highlighted the hair follicle's role in maintaining skin immune surveillance and suggested a mechanism for rapid immune recovery post-UVB exposure, involving 8 healthy adult volunteers.