Abstract
Introduction
Oral lichen planus (OLP) is a complex immunological disorder of oral mucosa, mediated in part by the release of cytokines by activated T-cells. Of late, two closely related T-helper (Th) cell subsets; regulatory T-cells (Tregs; FoxP3+) and Th17 cells (IL17+) have been described in various chronic inflammatory diseases. Tregs are essential in maintaining peripheral tolerance and regulating the immune response. Alternatively, Th17 cells play a critical role in several autoimmune diseases, inflammation and host defense. The factors that regulate IL17 expression are not well understood. Recently two novel cytokines, IL33 and IL35, have been described in some chronic inflammatory conditions. IL33, an essentially pro-inflammatory cytokine, is a member of the IL1 cytokine family, which promotes a Th2 immune response. IL33 has been shown to activate mast cells to produce IL17. IL35 is a heterodimer (EBI3 and p35) protein belonging to the IL12 cytokine family with an immuno-modulatory function. It is expressed by Tregs and suppresses the differentiation of Th17 cells, a source of the pro-inflammatory cytokine IL17. The role of the cytokines, FoxP3, IL17, IL33 and IL35 is yet to be investigated in OLP.
Hypothesis and Aims of the Investigation
FoxP3, IL17, IL33 and IL35 are expressed in OLP lesions and play a role in the pathogenesis of OLP. The main aim of the study was to determine the expression of FoxP3, IL17, IL33 and IL35 in OLP using immunohistochemistry and quantitative real-time reverse transcriptase polymerase chain reaction (qRT2-PCR).
Methodology
FoxP3, IL17, IL33 and IL35 expression was evaluated by immunohistochemistry (IHC) in formalin-fixed paraffin embedded (FFPE) archival specimens (n=23), divided into two groups; experimental OLP group (n=12) and a non-specific inflammatory (NSI) control group (n=11). Positive and negative controls were used to validate the IHC runs. Quantitative and qualitative analysis was done and the statistical significance risk rate was set at p 0.05. Immunofluorescence (IF) double-labelling was performed to determine the presence of IL33 and IL35 in CD3+ T-cells. In addition, twelve fresh tissue samples (experimental OLP group n=6 and NSI control group n=6) were used to determine the expression of FoxP3, IL17, IL33 and EBI3 (a component of IL35) genes by qRT2-PCR.
Results
In IHC, both OLP and NSI showed positive nuclear staining with FoxP3, IL17, IL33 and IL35 in the superficial connective tissue inflammatory infiltrate. Significantly more FoxP3+ cells were present in OLP than in NSI. IL17+ cells, on the other hand, showed significantly higher numbers in NSI than OLP. IL33+ and IL35+ cells did not show any significant difference between the groups, but were not shown to be expressed by T cells in IF double-labelling experiments. The gene expression experiments revealed a significantly higher expression of FoxP3 and EBI3 in OLP when compared to the controls.
Conclusion
Based on the results it was concluded that FoxP3+ Tregs are more likely to have a prominent role in the pathogenesis of OLP when compared to IL17, IL33 and IL35. IL33 and IL35 cytokines are not produced by T cells in OLP. However the cells expressing IL33 and IL35 and their precise role in pathogenesis of OLP needs further exploration.