Expression of cytokeratins in normal and neoplastic colonic epithelial cells. Implications for cellular differentiation and carcinogenesis.

Cells of the normal colonic mucosa express several types of cytokeratins, the characteristic intermediate filament proteins of epithelial cells. An immunohistochemical study was designed to examine the expression of two distinct groups of cytokeratins, recognized by monoclonal antibodies AE1 and AE3, in the colonic mucosa and to compare the findings with those obtained with a large number of polypoid lesions (adenomatous and hyperplastic) and carcinomas of the colon. AE1 and AE3 immunostaining was found in the surface epithelium and upper portions of the crypts of Lieberkühn (functional zone) of normal colonic mucosa, whereas the lower portions of the crypts (proliferative compartment) were unreactive with both AE1 and AE3. Polypoid lesions of the colonic mucosa can be placed into two categories based on their patterns of cytokeratin expression. Solitary tubular adenomas and hyperplastic polyps are composed of AE1 and AE3 nonexpressing cells with only few, patchy areas of AE1 and AE3 expressing cells present within glands and in the surface epithelium. In contrast, villous adenomas show strong AE1 and AE3 reactivity throughout the glands. Furthermore, tubular and villous adenomas, and even histologically normal mucosa in patients with familial polyposis, show AE1/AE3 expression throughout the glands and surface epithelium. Colonic carcinomas show a predominance of AE1/AE3 expressing cells. Thus, cytokeratins recognized by monoclonal antibodies AE1 and AE3 represent molecular markers of cellular maturation in the normal colonic mucosa, that are expressed in colonic carcinomas and, in addition, serve as markers that distinguish colonic mucosa and adenomas with a high risk for development of cancers from those with a lower risk.