Location and Fine Structure of Melanocytes in Human Fetal Scalp Hair Follicles

The study investigated the location and fine structure of melanocytes in human fetal scalp hair follicles. Researchers used scalp samples from a 6-month-old fetus, staining them with various antibodies and culturing the cells. They found that NKI/beteb positive cells were located in the outer root sheath, while cells in the hair bulb expressed HMB-45, tyrosinase, and TRP1 antigens. In vitro, two types of melanocytes were observed: one with abundant melanin that disappeared after passage, and another that proliferated rapidly but initially lacked melanin. After three passages, most cells were NKI/beteb positive. The study concluded that melanocytes in the outer root sheath are likely melanocyte stem cells or progenies, which proliferate quickly but remain morphologically and functionally immature, hindering melanosome transport.