Objectives The aim of this study is to investigate the mechanism of umbilical cord mesenchymal stem cells (UC-MSC) in the upregulation of peripheral regulatory T cells in patients with systemic lupus erythematosus (SLE).
Methods Peripheral blood mononuclear cells (PBMC) from 20 SLE patients and normal controls were co-cultured with UC-MSC at different ratios respectively for 72 hours, and the proportions of CD4+CD25+Foxp3+regulatory T cells were analyzed by flow cytometry. PBMC and serum from active SLE patients and normal controls were used to stimulate UC-MSC, TGF-β1 mRNA expressions on UC-MSC were detected by real-time fluorescence quantitative polymerase chain reaction (real-time PCR). Supernatant TGF-β1 levels were determined by enzyme-linked immunesorbent assay (ELISA). The TGF-β1 small interfering RNA (siRNA) was used to interfere TGF-β1 expression on UC-MSC, then to determine its effect on the regulation of SLE Treg cells. TGF-β1 inhibitor was added in the culture system of UC-MSC and PBMC from active SLE patients, to observe its role on the upregulation of Treg cells by UC-MSC.
Results UC-MSC could dose-dependently upregulate peripheral CD4+CD25+Foxp3+Treg proportion in SLE patients, which was not depended on cell-cell contact. UC-MSC had no regulatory effect on Treg cells in normal controls. Compared with the non-stimulated group and normal PBMC stimulated group, PBMC from SLE patients significantly promoted TGF-β1 mRNA expression on UC-MSC (relative gene expression was 1.00 ± 0.09,1.95 ± 0.62,4.20 ± 2.34, respectively, both P<0.05). Supernatant TGF-β1 levels were significantly elevated in the presence of SLE PBMC. Serum of SLE patients (5%) enhanced TGF-β1mRNAexpression on UC-MSC (12.19 ± 4.49), significantly higher than fetal bovine serum cultured group (1.33 ± 0.06, P<0.01) and normal individuals serum cultured group (2.53 ± 0.72, P<0.01). Additionally, TGF-β1 siRNA interfered UC-MSC failed to upregulate Treg cells in SLE patients (SLE PBMC + TGF-β1siRNA UC-MSC group 2.33% ± 0.99% vs.SLE PBMC group 1.80%±0.65%, P>0.05). Furthermore, TGF-β1 specific inhibitor SB431542 significantly inhibited the regulatory role of UC-MSC on Treg cells in SLE patients (SLE PBMC+UC-MSC+SB431542 group 4.58%±2.10% vs. SLE PBMC+UC-MSC group 7.85%±3.54%, P<0.05).
Conclusions Immune microenvironment in SLE patients can significantly stimulate TGF-β1 expression on UC-MSC, which plays an important role in the upregulation of Treg cells in patients. This study provides a new mechanism for the regulation of Treg cells by UC-MSC and treatment for SLE patients.
Disclosure of Interest: None Declared