Cell kinetic study of human and mouse hair tissues using anti-bromodeoxyuridine monoclonal antibody

To determine sites of cell proliferation in hair tissues, in vitro and in vivo labeling with bromodeoxyuridine (BrdU) and immunohistochemical demonstration of BrdU incorporation sites by anti-BrdU monoclonal antibody were performed on human and mouse hairs and hair follicles. The germinative area of the hair bulb of human anagen hair was divided into three portions: (A) the upper and inner portion, (B) the middle portion and (C) the lowest outer portion. A-cells intermingled with melanocytes, were regarded as germinative cells of the hair cortex. B-cells appeared to develop into Huxley's layer, cuticle of inner root sheath (IRS), and hair cuticle. C-cells seemed to develop into bulbar outer root sheath (ORS), the innermost cell (IMC) layer of the ORS and Henle's layer. The suprabulbar portion, where the ORS abruptly increased in thickness, was found to be the fourth main germinative portion (D). The ORS cells, except for the IMCs, seemed to originate mostly from the D-cells. In the late anagen phase, first, C-cells became BrdU negative, then, A- and B-cells gradually turned negative, and finally, D-cells lost their germinative activity. In catagen and telogen hair tissues, BrdU-positive cells were found in the two outer cell layers in the ORS. The structure of anagen hair tissues seems to be maintained by the coordinated mitotic activities of characteristically distributed germinative cells of various hair cell layers. The sequential cessation of mitotic activity of these cells is associated with the morphological changes from anagen through catagen to telogen. These findings were common to both human and mouse hair tissues.