Elevated levels of CD4(+)CD25(+)FoxP3(+) T cells in systemic sclerosis patients contribute to the secretion of IL-17 and immunosuppression dysfunction.

Xinjuan Liu,Qian Wang,Na Gao,Dong Xu,Henghui Zhang,Yong Hou,Mengtao Li,Xiaofeng Zeng,Guohua Zhang,Qiuning Sun,Song Guo Zheng

doi:10.1371/journal.pone.0064531

Abstract

ObjectiveImmune imbalance between regulatory T (Treg) and Th17 cells is a characteristic of systemic sclerosis (SSc). The functional heterogeneity among Treg can be elucidated by separating Treg into different subsets based on the expression of FoxP3 and CD45RA. The aim of this study was to investigate the role of Treg subsets in the immune imbalance in naïve SSc.MethodsPeripheral blood mononuclear cells (PBMCs) of 31 SSc patients and 33 healthy controls were analyzed for the expression of CD4, CD25, CD45RA, CTLA-4, FoxP3, and IL-17 using flow cytometry. Treg immunesuppression capacity was measured in co-culture experiments. The expression of FoxP3, CTLA-4, IL-17A, and RORC mRNA was measured by real-time PCR.ResultsThe frequency of CD4+CD25+FoxP3+ Treg cells was significantly elevated in patients with SSc (3.62±1.14 vs 1.97±0.75, p<0.001) with diminished immunosuppression capacity. In SSc, the proportion of FoxP3highCD45RA− activated Treg cells (aTreg) was decreased, the proportion of FoxP3lowCD45RA− T cells was increased, and the proportion of FoxP3lowCD45RA+ resting Treg cells (rTreg) was decreased. The immune suppression capacity of aTreg and rTreg was diminished, while FoxP3lowCD45RA− T cells exhibited a lack of suppression capacity. The immune dysfunction of aTreg was accompanied by the abnormal expression of CTLA-4. Th17 cell numbers were elevated in SSc, FoxP3lowCD45RA− T cells produced IL-17, confirming their Th17 potential, which was consistent with the elevated levels of FoxP3+IL-17+ cells in SSc.ConclusionA decrease in aTreg levels, along with functional deficiency, and an increase in the proportion of FoxP3lowCD45RA− T cells, was the reason for the increase in dysfunctional Treg in SSc patients, potentially causing the immune imbalance between Treg and Th17 cells.

Highlights

Systemic sclerosis (SSc) is a complex autoimmune disease, for which effective treatments are not yet available
The frequency of CD4+CD25+forkhead box P3 (FoxP3)+ Treg among peripheral blood mononuclear cells (PBMCs) in 31 SSc patients and 33 healthy controls was assessed by flow cytometry
The frequency of CD4+CD25+FoxP3+ Treg cells was significantly elevated in patients (3.6261.14) compared to healthy controls (1.9760.75, p,0.001; Figure 1A)

Summary

Introduction

Systemic sclerosis (SSc) is a complex autoimmune disease, for which effective treatments are not yet available. SSc is characterized by excessive collagen production resulting in skin and visceral fibrosis of various organs; the pathogenesis of SSc is not very clear. The pathophysiology of SSc can be summarized as a combination of microvascular damage, slowdeveloping fibrosis, and an abnormal immune system. Immunological activity, especially of T lymphocytes, is considered to be a key stimulus in promoting the vascular abnormalities and fibrosis observed in SSc [1]. Many studies implicate the immune system in the pathology of SSc via the presence of autoantibodies and elevated cytokine levels. Activated T lymphocytes, especially CD4+ T cells, are readily detected in the circulation and affected organs in SSc [2]

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