P5 DIFFERENT LOCATION OF THE IMMUNOHISTOCHEMICAL EXPRESSION OF CK 15 AND CD 34 IN HUMAN HAIR FOLLICLES
Jiménez F1, Poblet E2, Izeta A3
1Dermatology, Las Palmas de Gran Canaria, Spain
2Dept. Pathology, Universidad Castilla La Mancha, Albacete, Spain
3Fundación Inbiomed, San Sebastián, Spain

The presumptive niche for the hair follicle stem cells, the “bulge region“, is clearly identified in fetal human skin but barely visible in adult human hair follicles. This region corresponds to the insertion site of the arrector pili muscles. Immunohistochemical stainings with CD34 (human haematopoietic progenitor cell antigen) and CK 15 help to delineate the bulge region in mice; however, in humans, the location of the immunostaining with these two markers may be different. Vertical paraffin-embedded sections of adult human hair follicles in the anagen, catagen, and telogen phases were obtained from the scalp and immunostained with antibodies anti Cytokeratin 15 (CK15, clone LHK15, Novocastra) and anti CD34 (clone QBEnd 10, Dako). Both markers showed an intense staining in the epithelial cells of the outermost layers of the outer root sheath. CD34 staining was pericellular or membranous, while CK15 was mainly cytoplasmic. In anagen follicles, CK 15 is expressed at the level of the isthmus and at the insertion site of the arrector pili muscle. CD 34, in contrast, is expressed at the level of the inferior portion of the hair follicles, below the isthmus and above the matrix cells. CD34 tend to disappear in catagen and is not visible in telogen follicles. On the other hand, CK15 is intensely expressed in catagen and surrounds completely the club of the telogen follicle. In conclusion, the immunohistochemical location of CD34+ cells and the CK15+ cells in anagen follicles is very different in human follicles, presenting only a small area of confluence at the insertion of the arrector pili muscle. The staining pattern of CK15 appears to be almost the opposite to that showed by CD34 in anagen follicles. This different pattern of expression suggests that they either recognize different cells or cells in different stages of differentiation.