Abstract:

Objective To investigate the location, fine structure of melanocytes in human fetal scalp hair follicles. Methods The scalp with hair follicles was obtained from a dead fetus of 6 months of age, and divided into two parts. One part was embedded in paraffin, tissue sections were prepared with a width of 7 μm and stained with NKI/beteb, monoclonal antibodies to HMB-45, tyrosinase and tyrosinase-related protein 1 （TRP1）, respectively. The other part with hair follicles was treated with collagenase type Ⅱ 0.1 g/L and trypsin，then, cell suspension was collected and cultured. After 14-day culture, follicle melanocyte cells （FMC） were separated from keratinocytes by differential trypsinization, and fibroblasts were removed with geneticin. Following three times of pure passage, FMC were seeded and fixed on mica for scanning electron microscopy （SEM） and atomic force microscope （AFM） scanning. Results Histopathological examination showed that NKI/beteb positive cells located at the outer root sheath of human hair follicles, and these cells stained negatively for HMB-45, tyrosinase and TRP1 antibodies. However, in the hair bulb, lots of cells expressed HMB-45, tyrosinase and TRP1 antigens. After fibroblasts and keratinocytes were removed, two kinds of melanocytes remained in the culture: one was small in number and showed abundant melanin, which was lost after subsequent passage; the other was large in number and had no melanin initially, but proliferated very rapidly. After three passages, almost all the melanocytes were positive for NKI/beteb. As SEM and AFM showed, most cultured melanocytes appeared fusiform with two （rarely three） dendrites, and the cell body was round or oval with a few melanosomes scattered in but no clear secondary branches on the dendrites. Conclusions The melanocytes in outer root sheath of hair follicles from the fetal scalp are presumed as melanocyte stem cells or their progenies. In vitro, these cells proliferate very rapidly during early phases, but the morphology and function of them still remain immature, which is unfavorable for melanosome transport.

Key words: fetal;hair follicle;melanocyte;culture;identification