Unraveling the identity of FoxP3+ regulatory T cells in GPA-patients

Abstract

Background/Purpose: Human FoxP3+ Th-cells are heterogeneous in function and include not only suppressive cells (TRegs) but also nonsuppressive cells that abundantly secrete proinflammatory cytokines. We have previously shown that FoxP3+ Th-cells were increased in GPA-patients during remission as compared to healthy controls (HCs). In this group of patients, however, we observed a defective suppressor function of TRegs, and an increase in the percentage of Th-17 cells. These observations make it tempting to investigate whether increased FoxP3+ Th-cells in GPA-patients are attributed to an increase in the cytokine-secreting non-suppressive FoxP3+Th-cells. Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from 46 GPA-patients in remission and from 22 age- and sex-matched HCs. Expression of CD4, CD45RO, and FoxP3 were determined by flow cytometric analysis. The expression levels of FoxP3 and CD45RO were used for distinction between activated suppressor TRegs (FoxP3HighCD45RO+; ASTReg), resting suppressor TRegs (FoxP3LowCD45RO-; RSTReg), and cytokine-secreting non-suppressor TRegs (FoxP3LowCD45RO+; NONTReg) cells. Intracellular expression of IFNg, IL-17, and IL-21 were determined in the various FoxP3+ Th-cell subsets after in vitro activation of PBMCs by PMA and Ca-Ionophore. Results: A significant increase in the frequency of NONTReg cells was observed in GPA-patients as compared with HCs, whereas no differences were detected in RSTReg- and ASTReg cells between GPA-patients and HCs. The distribution of RSTReg- and NONTReg cells did not differ between ANCA-negative and ANCA-positive patients, whereas lower percentages of ASTReg cells were observed in ANCA-positive patients as compared to ANCA-negative patients and HCs. Importantly, a significant increase in the percentage of IL-17+ and IL-21+ cells was seen within the NONTRegcells from ANCA-positive patients (n= 9) when compared to ANCA-negative (n= 10) and HCs (n= 12), whereas no differences were found between ANCA-negative and HCs. Conclusion: Increased FoxP3 expression in Th-cells from GPA-patients is related to an increase in a subset of non-suppressive Th-cells. Increased production of IL-17 and IL-21 cytokines, in NONTReg cells from ANCApositive patients points towards FoxP3+ effector cells and decrease in suppressive TReg cells in relation to ANCA production.