Abstract: Objective To investigate the location and proliferation of human hair follicle stem cells. Methods The expression of keratin 19(K19) in the human hair follicles on the occiput was detected by immunohistochemical staining, and the positive area was located. The follicle epithelium containing the K19-positive area above the hair bulb were cultured with or without mesenchymes (dermal papilla cells, DPCs) at the air-liquid interface of the collagen gel. When the proliferating colonies formed, the distance from the colony to the bottom of hair follicles was measured and the relationship between the K19-positive position and the proliferation colonies was analyzed. The ultrastructure of the proliferation colony was observed by transmission electron microscopy. Results Two portions were found positive for K19 in the outer root sheath of the human hair follicles, the upper one being at the bulge region and the lower one at the outer root sheath above the hair bulb. The proliferating colony formed only when the epithelium of the hair follicle was co-cultured with mesenchymes cells. The statistical analysis suggested the lower portion positive for K19 and the proliferation colonies in the culture were traced to locate at the same site of the human hair follicles. Under electron microscopy, juvenile cells, mature keratinocytes and apoptotic cells were found in the proliferating colonies. Conclusions The human hair follicles may contain two distinct reservoirs for stem cells, which locate in the bulge area and in the region of the outer root sheath above the hair bulb, respectively. Mesenchymes are needed for the proliferation of stem cells. New stem cells, mature keratinocytes and apoptotic cells may be three endings of the stem cells' proliferation.

Key words: Hair follicle, Stem cells