The Role Of CD4~+Regulatory T Cells In The Mechanism For The Immunopathogenesis Of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterizedby the breakdown of self-tolerance, resulting in immune function disorders andautoantibodies to nucleus, cytoplasmic and cell surface moleculars. Increased rate of T-cellapoptosis and B cell hyperactivity abnormalities have been described, including defects ofquality and quantity in regulatory T (Treg) cells. Treg cells are different from the Th1andTh2cell populations and have immune regulatory function. They can play an importantrole in immune tolerance. Recently, the study about Treg cells becomes one of the mostpopular topics in immunology, because the abnormal of either frequency or function canresult in the imbalance of self-tolerance which can cause all kinds of autoimmune. Thefrequency and function of Treg cells have been widely analyzed in the past few years.However, contradictory results have been reported by different groups. It was reported thatthe frequency of Treg cells in the peripheral blood of patient with SLE were increased,decreased or not change. Besides, the function of Treg cells decline or constant are alsoreported. The differences in these data may be derived from patients from different races,in different stages of the disease, received a different treatment or the defining marks ofTreg cells were differently chosen by individual groups. In addition, more and moreevidence show that the Treg cells have a big family, which may include different cellsubsets with different functions and mechanisms. Therefore, research focus on thesubgroup of Treg cells may be more helpful in understanding immunopathogenesis of SLE.Inducible Costimulatory (ICOS) is a newly discovered costimulatory molecules expressedon activated T cells, belonging to the CD28/CTLA-4family. Although most previousstudies suggest that ICOS plays a positive costimulatory role for the effector T cells.However, the latest studies suggest that ICOS could also play an important role in immunetolerance. Based on the expression of ICOS, Treg cells can be divided into CD4+ICOS+Foxp3+T cell and CD4+ICOS-Foxp3+T cell subsets. The CD4+ICOS+Foxp3+T cellswere found to be able to produce highest mount of IL-10among the CD4+T cells pool. Itis possible that this subpopulation could be involved in the pathological mechanisms of avariety of tumors and autoimmune diseases. Despite the fact that the IL-10is considered ananti-inflammatory cytokine, some reports have demonstrated that it is unable to exert itsimmunosuppressive and anti-inflammatory effects in case of SLE. In contrast, IL-10mayposses a paradoxical pro-inflammatory effect in SLE by promoting the production of platelet-activating factor, inducing the apoptosis of T cells and stimulating the activation ofB cells. This study will detect the circulating frequency of CD4~+ICOS~+Foxp3~+T cell inpatients with SLE and explore their possible mechanisms for the immunopathologicaldamage of SLE.In view the important role of Treg cells in immune regulation of SLE, how to expandfunctional Treg cells for the cell therapy raised enormous interest in recent years. Earlystudies have found that fasting or caloric restriction could alleviate the symptoms ofautoimmune diseases, however, the mechanism responsible for the effect are not wellunderstood. We have known that during fasting, the level of the circulating leptin aredramatically reduced. Since leptin could limit the proliferation of Treg cells, we wonder ifthe fasting could affect the frequency or function of Treg cells. In this study, we try toresolve the issues raised above and the study was divided into two parts:The First Part: The Circulating Frequency ofCD4~+ICOS~+Foxp3~+T Cells in SLE and Correlation with DiseaseSeverityObjective: To investigate the frequency, possible categories and clinical significant ofCD4~+ICOS~+Foxp3~+T cells in the peripheral of patients with SLE.Methods: The frequency of circulating CD4~+ICOS~+Foxp3~+T cells was analysed byflow-cytometric analysis in32SLE patients,10rheumatoid arthritis patients and22healthy controls. Production of IL-10and mTGF-b by different CD4~+T-cell populationswas determined by intracellular cytokine staining. Plasma levels of IL-10and TGF-b weredetermined by enzyme-linked immunosorbent assay (ELISA).Results: The frequency of circulating CD4~+ICOS~+Foxp3~+T cells was significantlyincreased in SLE patients as compared with control groups. The elevated frequency ofCD4~+ICOS~+Foxp3~+T cells had a positive correlation with SLE Disease Activity Index(SLEDAI) scores and serum anti-dsDNA but a negative correlation with serum C3.Additionally, the CD4~+ICOS~+Foxp3~+T cells contained significantly higher percentages ofIL-10-producing cells than CD4~+ICOS~+Foxp3~+T cells. A significant positive correlationwas also observed between the frequency of CD4~+ICOS~+Foxp3~+T cells and the plasmalevel of IL-10in SLE patients. Conclusion: An increased frequency of circulating CD4~+ICOS~+Foxp3~+T cells wasobserved in patients with SLE, suggesting its potential importance in theimmunopathogenesis of SLE. Analysis of the CD4~+ICOS~+Foxp3~+T cells population may beuseful for the evaluation of lupus disease severity.The Second Part: Fasting-Induced Hypoleptinemia ExpandsFunctional Regulatory T Cells in Systemic LupusErythematosusObjective: To investigate the impact of fasting on the frequency and function of Treg cellsin lupus-prone mice and the role of leptin in the mechanisms.Methods: Wild type mice (wild type, WT), leptin-deficient mice (leptin,-deficient B6ob/ob, ob/ob), leptin receptor defects in mice (leptin recepter-deficient B6db/db, db/db)and of NZB/W mice were divided into three different groups respectively: the first groupof mice: as blank control (normal feeding); the second group of mice: fasted for48hoursbut supplied with water, while intraperitoneal injection of0.2mlPBS2times a day; thethird group of mice: fasted for48hours but supplied with water, while intraperitonealinjection of leptin dissolved in0.2mlPBS,2times a day. The frequency of circulating Tregcells (CD4~+CD25+Foxp3~+T cells) were detected by flow cytometry. The suppressionfunction of Treg cells were detected by CFSE and ELISA. The weight, spleen cellularityand plasma levels of leptin were also compared among three groups.Results: It was found that the increased frequency of Treg cells in starved WT and NZB/W mice could be reversed by leption replacement in these mice with no change of thefunction of Treg cells. In ob/ob mice,48h fasting have no significant effect on thefrequency and function of Treg cells; however, the replacement of leptin could decrease theratio of Treg cells. In db/db mice, either the frequency or the function had no changesamong the three groups.Conclusion: fasting can significantly increase circulating functional Treg cells in thelupus-prone mice. Leptin/leptin receptor pathway plays an important role in the mechanism.These observations help to explain the benefcial effects of fasting in autoimmunity andcould be exploited for leptin-based immune intervention in systemic lupus erythematosus.