Cytokeratin 15 expression in central, centrifugal, cicatricial alopecia: New observations in normal and diseased hair follicles

Background: Cytokeratin 15 (CK15) is a useful marker for the bulge zone (BZ) and has been used to examine follicles in cicatricial alopecia. We studied the expression of CK15 in hair follicles of patients with central, centrifugal, cicatricial alopecia (CCCA) in an attempt to define BZ integrity. Methods: A commercially available antibody to CK15 was used on formalin-fixed, paraffin-embedded tissue from clinically and histologically 'normal' scalps, clinically diseased scalps from patients with CCCA and clinically 'normal' scalps from patients with CCCA. Results: In both normal and diseased follicles, CK15 expression was closely linked to anatomical zone cellular morphology. Normal and abnormal inner root sheath (IRS) desquamation occurred in concert with predictable cellular morphological changes and CK15 expression. In most abnormal follicles, once the IRS desquamated, the morphology of BZ epithelium changed and CK15 expression disappeared. Conclusions: CK15 highlights BZ cells in normal human follicles, but may be unreliable for this purpose in diseased follicles. CK15 should not be the sole marker for studying stem cells in cicatricial alopecia because any disease-induced structural changes could alter CK15 expression. More sophisticated studies of stem cells will be required to reliably define their role in the pathogenesis of cicatricial alopecia.