Identity of TUNEL-positive cells in the oral buccal epithelium of normal mucosa and lichen lesions

Background: In situ detection of DNA fragmentation by TdT (terminal deoxynucleotidyl transferase)‐mediated dUTP nick end labeling (TUNEL) is a widely used technique to identify apoptotic cells in the terminal phases of cell death. Several studies have shown that there are statistically increased numbers of TUNEL+ cells within the epithelium of oral lichen (OL). It was suggested that this indicates an increased rate of apoptosis among basal and suprabasal keratinocytes in OL epithelium. The aim of this study was to identify the TUNEL+ cells in the epithelium of erythematous (ERY) OL and normal oral mucosa (NOM). Methods: Sections of biopsies from NOM and ERY OL were processed for TUNEL combined with immunostaining for pan‐cytokeratin or for cell markers specifically expressed by different leukocytes. Results: In NOM, TUNEL+ keratinocytes were almost exclusively seen in the outermost epithelial layers. This labeling was absent in ERY OL. In the basal and lower spinous layers, more TUNEL+ cell nuclei were seen in ERY OL as compared with NOM, in accordance with previous studies. The present observations show, however, that only very few of these cells were keratinocytes, but rather were CD4+ lymphocytes and CD68+ macrophages. There was no difference between the numbers of TUNEL+ keratinocytes in basal and lower spinous layers in ERY OL and NOM epithelium. No intraepithelial CD8+ lymphocytes, Langerhans cells, or mast cells were found to be TUNEL+. Conclusion: The findings indicate that the pathologic changes in ERY OL epithelium cannot be explained by increased prevalence of terminal keratinocyte cell death identified by TUNEL.