[Immunohistochemical study on the keratin expression in generating rat hair tissues using anti-hair keratin monoclonal antibodies].

To investigate keratin expressions of generating rat hair tissues, monoclonal antibodies, HKN-2, 4, 5 and 6, were immunohistochemically applied on the skin specimens from 19-day-old rat fetus, newborn, 3-day-old and 7-day-old rats. In anagen hair tissues of 7-day-old rats, HKN-2 reacted with developing cells of the medulla, cortex, hair cuticle and inner and outer root sheaths. In the epidermis, HKN-2 reacted with spinous through horny cells. HKN-4 displayed a broad reactivity with all of the skin epithelial cells including hair tissue. These reactions were first seen in hair peg stage. HKN-2 and 4 first showed strong reactions with the innermost cell layer of the outer root sheath in anagen hair tissues of newborn rats. Reactivities by HKN-5 and 6 were localized in hair tissues in rats; however, HKN-5 showed no reaction with the innermost cell layer of the outer root sheath. HKN-5 and 6 showed no reaction with hair tissue before anagen. It is concluded that hair germ is different from epidermal basal cells in keratin expressions, that hair-specific keratins seem to be produced after the morphological differentiation of each layer, and that the innermost cell layer may differ from other outer root sheath since hair generation.