Hair development and Langerhans cell migration during human embryogenesis

Abstract

Hair follicles are immune privilege sites that protect multipotent stem cells. The location of the stem cells in the bulge area not only shields these crucial cells from environmental factors, but also protects them from immune-mediated injury. Hair follicles are considered to be reservoirs of Langerhans cells (LC). Although LC are known to migrate from the bone marrow, little is known about the mechanisms by which human LC locate to their appropriate position during embryogenesis. In contrast, melanocytes originate from the neural crest and migrate from the dorsal neural tube to the ventral side during embryogenesis. After completing migration, melanocytes are supplied from the bulge area of the hair follicles. To examine the relation between hair follicles, melanocytes, and LC during human embryogenesis, we obtained 4-mm punch biopsies from 4 specific sites (scalp, back, abdomen, and right sole) of 38 aborted fetuses following approval by the institutional review board. Immunohistochemical studies were then performed. Human embryo LC first appeared at 16 to 18 weeks gestation (WG). Before 16 WG, few LC were observed at any site, but the melanocytes had already completed their migration to the epidermal compartment where hair follicles had not yet developed. Hair follicle buds appeared and immature small LC were largely located there in the back and abdomen. LC appeared at the apertural area of eccrine sweat gland ducts in the sole, called the acrosyringial area, at 16 to 19 WG. Thus, the melanocytes first migrated to the hair follicle formation sites and then LC migrated to the hair follicle site, which is an immune-privilege site. These findings suggest that LC develop immunoregulatory properties at the hair follicle site during embryogenesis. JSID AbstractsJournal of Dermatological ScienceVol. 69Issue 2Preview Full-Text PDF