Background: Oral lichen planus (OLP) is a T-cell-mediated disorder of oral mucosa and is mainly observed in middle-aged adult women. The etiology of OLP is unclear.Objective: This study investigates the potential role of serotonin in the pathogenesis of OLP, thourgh evaluation of the immunohistochemical expression of serotonin (5-HT) in biopsies from patients with OLP and its association with clinicopathological findings. /Patients and methods: Paraffin-embedded tissue samples were histologically confirmed as OLP. Monoclonal antibody serotonin was used for immunohistochemical staining. The patterns of positively stained cells were analyzed using semiquantitative techniques. Results: A total 40 biopsies from 24 female and 16 male OLP patients were involved. The mean age was 49.15 (SD 11.39) years. Using an immunohistochemical method, the results showed that the intensity of expression of 5-HT at the basal layer was established in 11 (27.5%) cases who had grade 0, 18 (45%) cases had grade 1, and 11 (27.5%) cases had grade 2, with a median H-index of 55 ranging between 0-200. The intensity of 5-HT expression at the suprabasal layer showed that 7 (17.5%) cases had grade 0, 15 (37.5%) cases had intensity grade 1, 16 (40%) cases had intensity grade 2, and only two (5%) cases had grade 3, with a median H-index was 80, ranging between 0-300. The median total H-index was 153.5 (SD 111.5), ranging between 0-500. Conclusions: Serotonin has been proven in the epithelium of oral lichen planus in most studied cases, which is considered an important marker in its pathogenesis.

Introduction oral lichen planus (OLP) is a common oral mucosal disease with various clinical manifestations. The most predominant types are reticular and erosive. Despite extensive research on the causes of OLP, the exact etiology remains unclear. However, it is believed that a T-cell-mediated response, which triggers the apoptosis of oral epithelial cells, may contribute to the development of this disorder. This study aims to investigate the different types of T-cells (specifically CD4 and CD8) present in OLP tissue samples. By using immunohistochemistry, the expressions of cluster of differentiation 4 (CD4) and cluster of differentiation 8 (CD8) will be evaluated in biopsy samples taken from OLP patients who exhibit various clinical presentations. Methods this study was a retrospective analysis study. Oral lichen planus was established histologically in forty paraffin-embedded tissue samples. Blocks of OLP were diagnosed and characterized as reticular or erosive. Immunohistochemical staining was conducted using a monoclonal antibody for (CD4) and a polyclonal antibody for CD8. Semi-quantitative techniques were used to analyze the patterns of positively stained cells. Results: forty biopsies of OLP cases were obtained from 24 females and 16 males. The mean age was (49.15±11.39) years. Using an immunohistochemical method, the proportion of CD4 expression: CD8 expression among the epithelial-connective tissue interface was shown to be 24 (60%) cases with a predominance of CD8, 9 (22.5%) cases with no difference, and only 7 (17.5%) cases with a predominance of CD4. The proportion of CD4: CD8 among perivascular parts was shown to be 8 (20%) cases with a predominance of CD8, 20 (50%) cases with no difference, while only 12 (30%) cases had a predominance of CD4. The CD4 perivascular expression was significantly stronger in (71.4%) of erosive OLP than in reticular cases. Conclusion T-cell subsets (CD4 and CD8) were found in the OLP infiltrates. The correlation may have contributed to the pathogenesis of OLP.