Differential expression of keratin 19 in normal human epithelial tissues revealed by monospecific monoclonal antibodies

Three monospecific monoclonal antibodies (BA16, BA17 and A53-B/A2) recognizing different epitopes of the human keratin 19 were used to determine tissue distribution of this 40 kDa keratin polypeptide. Immunohistochemical methods revealed four different staining patterns among normal human epithelial tissues: firstly, complete negativity of the epidermis, sebaceous glands, hepatocytes and other tissues; secondly, homogeneous positivity as seen for example in the gall bladder and urinary bladder epithelium, endometrium and many other epithelia; thirdly, a mosaic of positive and negative cells among mammary gland luminal cells, prostate epithelia and some other epithelia and fourthly, a more complex heterogeneous pattern found in non-keratinizing squamous epithelia and hair follicles with generally the basal layer being the most strongly or sometimes exclusively stained. The pattern seen in non-keratinizing squamous epithelia varied considerably according to the fixation method and the antibody used as well as among different donors and in different areas of the same organ. The other three staining patterns were on the other hand nearly identical with all three antibodies on both frozen sections and sections of methacarn-fixed paraffin-embedded tissues. Our results provide evidence for differential expression of the human keratin 19 at the single cell level, an observation which could be exploited in the study of epithelial differentiation and pathology.