Keratins as molecular markers of epithelial differentiation: differential expression in crypt epithelium of human palatine tonsils.

The expression of keratins in the stratified squamous nonkeratinizing epithelium lining the surface and the crypts of human palatine tonsils was analyzed by high-resolution gel electrophoresis, immunoblotting, and immunohistochemical techniques. In contrast to the superficial epithelium, which showed a fairly constant keratin composition consisting of the neutral-to-basic keratins K4, K5, K6, and K8 and the acidic keratins K13, K14, K16, and K19, the keratin profiles of tonsillar crypt epithelial cells were found to be more variable, particularly with respect to the expression levels of K4 and K13. These were identical to those of surface epithelium, reduced, or abolished. Since K4 and K13 characterize the mature stage of differentiation in squamous nonkeratinizing epithelia, their decrease is indicative of an incomplete epithelial differentiation. Immunohistochemical analyses confirmed this hypothesis and allowed us, furthermore, to correlate the expression of K13 with the morphologic alterations of tonsillar crypt epithelium in the course of reticulation.