Functional Down-regulation Of CD4+CD25+ Regulatory T Cells By IL-6/Stat3 Pathway In Oral Lichen Planus

Objectives:Oral lichen planus?OLP?is a T cell-mediated autoimmune disease,CD4⁺CD25⁺regulatory T cells?Treg?plays a critical role in the maintenance of immune homeostasis and prevention of autoimmunity.Previous studies have demonstrated that the proportion of CD4⁺CD25⁺T cells in OLP patients was significantly higher and may contribute to the pathogenesis of OLP.Serum level of IL-6 in OLP patients was significantly higher than healthy controls,and the existing research has confirmed that IL-6/Stat3 signaling contributes to impaired function of regulatory T cell.In this study,we intend to explore that whether there is intrinsic defect or secondary dysfunction of CD4⁺CD25⁺regulatory T cells,and the possible mechanisms underlying this dysfunction.Methods:Flow cytometry and ELISA,Realtime-PCR,magnetic bead separation,cell coculture,molecular biology techniques were applied to the following aspects:?1?The number of Foxp3⁺T cells in peripheral blood and oral lisions;?2?Related cytokines in serum and oral lesions;?3?OLP CD4⁺CD25⁺T cells in vitro inhibitory function;?4?IL-6 involved CD4⁺CD25⁺T cells in vitro inhibitory function;?5?IL-6-mediated phosphorylation of Stat3 in Treg.Results:?1?Increased proportions of Tregs were found in OLP patients,both in peripheral blood and oral lisions.?2?The expression of FOXP3 on mRNA and protein level was elevated in the Tregs of OLP.The expression of TGF-?was lower both on the mRNA and serum level,whereas the expression of IL-10 showed no significant difference between the OLP patients and normal controls.mRNA expression of EBI3,IL-12A,T?RI and T?RII did not differ statistically among the different groups.The percentages of CD4⁺Foxp3⁺IL-17⁺T cells were significantly higher than that of normal controls,whereas the percentages of CD4⁺Foxp3⁺IFN-?⁺T cells did not differ significantly.?3?Suppressive function of CD4⁺CD25⁺Treg cells from OLP patients was impaired.Suppressive function of CD4⁺CD25⁺Treg cells of crossover experiments indicated no resistance of effector T cells to suppression of Treg.?4?Expression of IL-6R was elevated in the CD4⁺CD25⁺CD127^low/-T cell subset of OLP patients.The serum level of IL-6 in both the reticular and erythematous/erosive groups was significant higher when compared with normal controls.Expression of IL-6 mRNA by lesional keratinocytes was statistically higher than that of normal controls.mRNA levels of Stat3 did not differ statistically among the different groups.?5?IL-6 signaling prevents the suppressing functions by Treg from OLP patients.Both of phosphorylated Stat3 of OLP and normal CD4⁺CD25⁺Treg cells elevated in response to IL-6,and the former was obviously more senstive to IL-6.Conclusions:These data indicate that Tregs in OLP are frequently expanded,with Foxp3 expression increased,but might be functionally impaired,with TGF-?expression decreased and IL-17A expression elevated.In addition,the suppressive function of Treg cells from OLP patients was impaired,and IL-6,whose levels were elevated in sera and oral lesions,could further impaired the suppressing activities of OLP Treg.This process might was done through IL-6-IL-6R-Stat3 pathway.This could explain,at least in part,why the increased Tregs in OLP fail to control the pathogenesis and development of this autoimmune disease.