Background: Age-related changes in proliferative activity in human gingival epithelium are uncertain. Proliferating cell nuclear antigen (PCNA) is a nuclear protein associated with the cell cycle. Nuclear PCNA immunoreactivity is found in the proliferative compartment of normal tissues. The aims of this study were to investigate the localization of PCNA expression in oral gingival epithelium (OGE) and to define the age-related changes as to PCNA-proliferative index (PI) in inflamed as well as healthy gingiva. Mitotic index (MI) was also used as a conventional marker of cell proliferation. Additionally, the effect of aging upon the maximum epithelial thickness (MET) was determined.
Methods: Twenty older (65 to 85 years) (study) and 20 middle-aged (35 to 45 years) (controls) subjects were included in the study. Biopsies were obtained both from healthy and inflamed gingiva. The expression of PCNA was evaluated in formalin-fixed, paraffin-embedded gingival samples using an immunoperoxidase technique and PC 10 monoclonal antibody to PCNA. Hematoxylin and eosin stained sections were used for the quantitative measurement of MI and MET.
Results: All the tissue sections contained positive staining cells for PCNA in the gingival epithelium. Although PCNA expression was observed both in the basal and suprabasal layers, it was more prominent in the suprabasal layers. PI in inflamed gingiva was significantly higher in the older group. However, no significant difference was observed between the study and control groups with respect to PI in healthy gingiva. When all the subjects taken into the study were analyzed as a single group, PI in the inflamed gingival samples were found to be increased with aging. Nevertheless, no age-related change was noted in MI and MET. In both the study and the control groups, PI, MI, and MET were found to be increased due to inflammation.
Conclusions: Our data indicate that PCNA expression in inflamed gingiva is higher in older subjects. Furthermore, a significant correlation was noted between aging and PCNA expression in inflamed gingiva. As there is no increase in mucosal epithelial thickness despite increased proliferation, we speculate that the duration of the PCNA+ phase in cell cycle may be longer in older subjects. This study also implies that PCNA immunolocalization can be used as an index of the state of cell proliferation in both biological and pathological events of the gingiva and/or other mucosal tissues.