Growth factor and growth factor receptor localization in the hair follicle bulge and associated tissue in human fetus.

The bulge region of the hair follicle has been thought to contain follicular stem cells. The bulge in the human follicle is a collection of undifferentiated cells that is prominent only in the fetal period. Antibodies that recognize epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), EGF receptor, platelet-derived growth factor (PDGF) A and B chains, PDGF alpha and beta receptors, and the low-affinity nerve growth factor receptor (p75) were used to study the bulge and associated mesenchymal cells in this fetal period. Weak EGF and TGF-alpha immunoreactivities were seen in the bulge. Confocal laser scanning microscopic images revealed intracytoplasmic and intranuclear punctate patterns of immunoreactivities in the bulge cells labeled by anti-EGF and anti-TGF-alpha antibodies. All the bulge cells stained strongly for EGF receptor. Cells within the bulge were labeled both with PDGF A chain and with PDGF B chain, although the immunoreactivities were weak in the outermost layer of cells. The follicular sheath was strongly immunoreactive with antibodies against both PDGF alpha and beta receptors. p75 was expressed in mesenchymal cells around the hair follicle and in the lower portion of the bulge. These differential labeling patterns suggested that EGF, TGF-alpha, and nerve growth factor may be involved in regulation of the growth and differentiation of bulge cells and that PDGFs may have related functions in the interaction arising between the bulge and associated tissue during follicle morphogenesis.