Disturbed expression of ribonucleotide reductase and cytokeratin polypeptides in focal epithelial hyperplasia: An immunohistochemical study using monoclonal antibodies

Four cases of focal epithelial hyperplasia (FEH) were studied immunohistochemically, using monoclonal antibodies against the M1 subunit of ribonucleotide reductase and different cytokeratin polypeptides. The FEH lesions showed, compared to normal oral mucosa, extensive alterations in their staining patterns. This included ectopic suprabasal M1 staining and the novel expression of cytokeratin polypeptides differing from those previously reported for other HPV infections. The results arc discussed in relation to the causative agent, human papillomuvirus, and its expression in focal epithelial hyperplasia.