Characterization of a Novel Human Type II Epithelial Keratin K1b, Specifically Expressed in Eccrine Sweat Glands

In this study, we show that a novel human type II epithelial keratin, K1b, is exclusively expressed in luminal duct cells of eccrine sweat glands. Taking this luminal K1b expression as a reference, we have used antibodies against a plethora of epithelial keratins to systematically investigate their expression in the secretory globule and the two-layered sweat duct, which was divided into the intraglandular, intradermal, and intraepidermal (acrosyringium) segments, the latter being further subdivided into the sweat duct ridge and upper intraepidermal duct. We show that (i) each of the eccrine sweat gland tissue compartments expresses their own keratin patterns, (ii) the peripheral and luminal duct layers exhibit a sequential keratin expression, with both representing self-renewing cell layers, (iii) the intradermal duct and the sweat duct ridge display hitherto unknown length variations, and (iv) out of all cell layers, the luminal cell layer is the most robust layer and expresses the highest number of keratins, these being concentrated at the apical side of the cells to form the cuticle. We provide evidence that the cellular and intercellular properties of the peripheral and the luminal layers reflect adaptations to different functions.