Supplementary Material for: In vitro Conversion into CD4+CD25+Foxp3+ Induced Regulatory T Cells Is Reduced in Atopic Dermatitis Patients

Background: Atopic dermatitis (AD) is one of the most common inflammatory skin diseases, with an increasing incidence in clinical practice. AD models have demonstrated that TGF-β signaling is compromised in regulatory T cells (Tregs). Objectives: This study aimed to investigate the TGF-β-dependent in vitro conversion of CD4+CD25– T cells derived from AD-patients into CD4+CD25+Foxp3+ induced Tregs (iTregs) in comparison to healthy controls. Methods: To analyze in vitro iTreg conversion, human CD4+CD25– T cells were cultured on anti-CD3-coated plates in the presence of TGF-β and IL-2 for up to 3 days. Consequently, the underlying mechanism of impaired CD4+CD25+Foxp3+ iTreg generation was explored by focusing on TGF-β signaling. Finally, the functionality of iTregs was investigated. Results: Conversion of CD4+CD25–Foxp3– into CD4+CD25+Foxp3+ iTregs was diminished in AD individuals. Impaired iTreg generation was accompanied by a reduced surface expression of GARP (glycoprotein A repetitions predominant), a marker for activated Tregs. A reduced expression of Smad3 mRNA was revealed in CD4+CD25– T cells. Interestingly, the suppressive quality of iTregs was found to be equal in cells derived from AD and healthy donors. Conclusion: The signaling effect of TGF-β receptors on the suppressor quality of iTreg conversion is conserved. Impaired iTreg generation might be a reason for the lack of immune suppression in AD patients and contributes to the chronicity of the disease.