RESUMO
<p><b>OBJECTIVE</b>To examine the expression of Fas and Fas ligand (FasL) in T lymphocytes of oral lichen planus (OLP) and the effects of Fas, FasL and activation-induced cell death (AICD) on OLP.</p><p><b>METHODS</b>The oral mucosa samples from patients with OLP and normal oral mucosa were assessed by in situ terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine-5'-triphosphate (dUTP)-biotin nick end-labelling (TUNEL) assay for nucleosomal DNA fragmentation of apoptotic cells in infiltrating lymphocytes. Immunohistochemical technique was used for detection of expression level of Fas and FasL. Immunohistochemical double labeling was performed to examine the expression of Fas and FasL in CD8+ T cells and CD4+ T cells.</p><p><b>RESULTS</b>The rate of apoptosis in infiltrating lymphocytes of OLP was (1.9 +/- 1.8)%, which was lower than that of normal oral mucosa (P = 0.013). The expression of Fas and FasL were increased in lymphocytes of OLP (P = 0.005 and 0.000 respectively). The positive rate of double labeled cells of CD8+ and Fas+ was not increased in OLP (P = 0.313), and of CD8+ and FasL+ in OLP was higher than that of normal oral mucosa (P = 0.002). The expression of double labeled cells of CD4+ and Fas+ in OLP was higher than that of control group (P = 0.031). The expression of CD4+ and Fas+ T cells in reticular OLP were increased (P = 0.019), and of CD4+ and FasL+ did not show remarkable change (P = 0.097).</p><p><b>CONCLUSIONS</b>There was a low frequency of lymphocytic apoptosis. T cells, especially CD8+ T cells in OLP and CD4+T cells in atrophic-erosive OLP appeared to escape from AICD, which may account for the persistence of inflammation. Some CD4+ T cells in reticular OLP may go through AICD.</p>