Cell Differentiation in Human Anagen Hair and Hair Follicles Studied with Anti-Hair Keratin Monoclonal Antibodies

By a hybridoma technique using BALB/c mice and Sp2/0-Ag14 mouse myeloma cells, monoclonal antibodies against hair fibrous proteins (HFP) were produced. Two monoclonal antibodies, designated as HKN-5 and HKN-7, were chosen. Either HFP or epidermal fibrous proteins (EFP) were electrophoretically separated on polyacrylamide gels with sodium dodecyl sulfate. By immunoblot analyses, HKN-5 and HKN-7 decorated the electrophoretic bands of HFP but not those ot EFP. Immunohistochemically, these monoclonal antibodies stained the medulla, cortex, cuticle, and inner root sheath in the keratogenous zone of anagen hairs, but not hair matrix cells. HKN-5 further reacted with the innermost cells (IMG) of the outer root sheath; these cells formed a single cell layer located outside of the Henle's layer. HKN-7 did not react with the outer root sheath including the IMG. Neither monoclonal antibody reacted with any other skin components or any tissues of other organs examined. Ultrastructurally, the IMG of the outer root sheath showed a unique cell differentiation forming an independent cell layer. It is suggested that the cells in the medulla, cortex, cuticle, and inner root sheath of anagen hair and hair follicles possess a similar keratin expression and that the IMC of the outer root sheath display a unique keratin expression and their own cell differentiation, resulting in 2 types of keratinization of the outer root sheath; keratinization of IMG and trichilemmal keratinization