Background Soluble human leukocyte antigen-G (sHLA-G) is a non-classical HLA class I molecule, exhibiting strong immunosuppressive properties by inducing the differentiation of T regulatory cells (Treg). Mesenchymal stem cells (MSCs) transplantation alleviates disease progression in systemic lupus erythematosus (SLE) patients. However, the underlying mechanisms are largely unknown.

Objectives The aim of the present study is to explore whether sHLA-G is involved in upregulating Treg cells by MSCs, which contributes to therapeutic effects of MSCs transplantation in SLE.

Methods The serum sHLA-G levels of SLE patients and healthy controls were detected by ELISA. The percentages of peripheral blood CD4 + ILT2 +, CD8 + ILT2 +, CD19 + ILT2 + cells and Treg cells were determined by flow cytometry. Ten patients with active SLE, refractory to conventional therapies, were infused with MSCs and serum sHLA-G was measured 24 h after infusion. Peripheral blood mononuclear cells (PBMCs) were isolated from SLE patients and co-cultured with UC-MSCs for 3 days at different ratios (50:1, 10:1, and 2:1) with or without anti-HLA-G antibodies, and the frequencies of CD4 + CD25 + Foxp3 + T cells were then determined by flow cytometry.

Results The concentrations of serum sHLA-G were comparable between SLE patients and healthy controls. However, there was a negative correlation between sHLA-G levels and SLE disease activity index (SLEDAI) scores in active SLE patients (SLEDAI >4). We found that serum sHLA-G levels were negatively correlated with blood urea nitrogen, serum creatinine and 24-hour urine protein in SLE patients. The sHLA-G levels were significantly lower in SLE patients with renal involvement than those without renal involvement. The expression of ILT2 on CD4 + T cells from SLE patients decreased significantly compared to that of healthy controls. A positive correlation between the frequencies of Treg and CD4 + ILT2 + T cells was found in SLE patients. The levels of sHLA-G increased 24 h after UC-MSC transplantation. The frequencies of Treg cells and the expressions of ILT2 on CD4 + Tcells were significantly increased 24 h after transplantations. In vitro studies showed that MSCs increased the frequency of Treg cells in SLE patients in a dose-dependent manner, which was partly abrogated by the anti-HLA-G antibody.

Conclusions Our results suggested that MSCs might alleviate SLE through upregulating Treg cells, which was partly dependent on sHLA-G.

Disclosure of Interest None declared