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Expression of hair follicle stem cell markers CD34 and CK15 in scarring alopecia

Introduction Pathogenesis of scarring alopecia (SA) is poorly understood with recent studies implicating loss of follicle stem cells (FSC). Objectives The aim of the present study was to examine the expression patterns of FSC markers CK15 and CD34 in SA and to compare them with biopsies from normal and non-SA cases. Materials and methods Twenty-one cases of SA were assessed using CK15 and CD34 immunostains. Biopsies from normal scalp and alopecia areata (AA) cases were studied for comparison. Results CD34 was expressed in the outer root sheath of the lower segment of follicles in all normal, 33% of the AA and 33% of the SA cases. CK15 was seen in the outer root sheath of the upper segment of hair follicles in 100% of normal and AA biopsies, compared with 91% of SA. CK15 was expressed in the lower segment of the follicle in 9/10 cases of SA, which is hitherto undescribed. CK15 was also retained in the bulge in 84% of the SA cases. Conclusion CD34 FSCs are lost in most SA cases. CK15 FSC are retained in both the bulge and the rest of the follicle, signifying that stem cell destruction alone does not eventuate in hair loss. The aberrant distribution of CK15 also suggests that there may be compensatory mechanisms yet to be understood.