CD10 and CD34 in fetal and adult human hair follicles: dynamic changes in their immunohistochemical expression during embryogenesis and hair cycling.

BACKGROUND CD10 and CD34 have been detected in both epithelial and mesenchymal components of anagen human hair follicles. OBJECTIVES To analyse the expression of CD10 and CD34 in human hair follicle development as well as in different phases of the hair cycle. METHODS Fetal and adult hair follicles at different stages of the hair cycle were examined by immunohistochemistry for CD10 and CD34. RESULTS In fetal follicles, CD10 is expressed by the cells of the placodes, and CD34 by the mesenchymal cells of the dermal condensate. As the follicle matures, CD10 can be seen in the matrix cells, inner root sheath and dermal sheath. In adult follicles, the expression of CD10 in the follicular epithelium is present in anagen follicles, but tends to disappear in catagen, and is not detected in telogen. The CD10 positivity of the dermal sheath is more intense in catagen than in anagen follicles. CD34 immunostaining of the external root sheath was seen in adult anagen follicles but not in fetal follicles. This staining of the anagen outer sheath tends to disappear in catagen and is not detected in telogen. CONCLUSIONS CD10 and CD34 are not proteins constantly present in a specific cell type of the hair follicle, but are proteins that can be expressed by both epithelial and mesenchymal cells depending on the stage of development and hair cycle. The distribution of the immunoreactivity to CD10 in the placode and CD34 in the dermal condensate suggests a role of these proteins in initial stages of hair formation.