The Immunohistochemical Expression of CD34 in Human Hair Follicles: a Comparative Study with the Bulge Marker CK15

Background: Anti-CD34 antibodies label the bulge region of mouse hair follicles. However, in human hair follicles, CD34 immunoreactivity is found in the outer root sheath below the bulge zone. The immunohistochemical staining of CD34 in catagen and telogen follicles has not been evaluated.

Aims: To characterize the expression of CD34 immunoreactivity at different stages of the hair cycle in human terminal hair follicles, and to compare the immunostaining pattern of CD34 with that of CK15, used here as a marker of the bulge region.

Method: Serial vertical sections of human hair follicles in anagen, catagen and telogen phases were immunostained with anti-CD34 (QBEnd 10) and anti-CK15 (LHK15 and C8/144B) antibodies. Double-labelling immunofluorescence was also performed.

Results: The catagen and telogen follicles studied did not show CD34 immunoreactivity in the outer root sheath. The location of CD34 and CK15 immunoreactivity in anagen follicles reveals a different staining pattern: CD34-positive cells are located in the outer root sheath below the attachment zone of the arrector pili muscle, whereas CK15-positive cells are located in the outer root sheath above the attachment zone of the arrector pili muscle.

Conclusions: Only anagen human hair follicles show CD34 immunoreactivity. CD34 and CK15 recognize different types of cells or cells at different stages of differentiation.