Distribution of cytokeratin polypeptides in epithelia of the adult human urinary tract

Cytokeratin expression was studied in the epithelia lining the normal human urine conducting system using immunohistochemistry on frozen sections employing a panel of 14 monoclonal antibodies. Eleven of these anticytokeratin antibodies reacted specifically with one of the 19 human cytokeratin polypeptides. Profound differences were found in the cytokeratin expression patterns between the different types of epithelium in the male and female urinary tract. In the areas showing morphological transitions of transitional epithelium to columnar epithelium and of nonkeratinizing squamous epithelium to keratinizing squamous epithelium gradual shifts of cytokeratin expression patterns were observed, often anticipating the morphological changes. However, also within one type of epithelium, i.e. the transitional epithelium, two different patterns of cytokeratin expression were found. Expression of cytokeratin 7 was homogeneous in the transitional epithelium of renal pelvis and ureter but heterogeneous in the transitional epithelium of the bladder. Furthermore, intraepithelial differences in cytokeratin expression could be shown to be differentiation related. Using a panel of chain-specific monoclonal antibodies to cytokeratins 8 and 18 conformational and/or biochemical changes in the organization of these intermediate filaments were demonstrated upon differentiation in columnar and transitional epithelium.