Objectives: Research indicates that low doses of interleukin-2 (IL-2) can effectively mitigate RA symptoms by promoting Treg cells, while high doses may enhance immune responses. Consequently, this study employed mutated IL-2 to minimize its impact on CD8 + T and NK cell activation while preserving its influence on Treg cells. Methods: We constructed IL-2 mutants by overlap PCR and assessed its impact on the proliferation and functionality of Treg cells by flow cytometry and PCR. Furthermore, the synergistic effects of mutated IL-2 and MSC on collagen-induced arthritis (CIA) in mice were evaluated through the infusion of lentiviral-transfected mesenchymal stromal cell (MSC) for CIA treatment and through pathological section staining to assess inflammatory joint injury, cartilage destruction, and osteoclast infiltration. Results: Mutant IL-2 demonstrated targeted enhancement of both the proportion and proliferative activity of Treg cells with a diminished capacity to stimulate the proliferation of CD8 + T cells and NK cells relative to wild-type IL-2. Moreover, MSC-mutant IL-2 significantly augmented the proportion of Treg cells compared to either MSC or mutant IL-2 in isolation. Treatment with MSC-mutant IL-2 infusion in CIA mice ameliorated arthritis symptoms and reduced inflammatory infiltration and cartilage damage in their joints. Conclusion: Mutant IL-2 enhances Treg function and proliferation while exerting reduced effects on CD8 + and NK cell activation. MSC expressing mutant IL-2 demonstrates therapeutic benefits in CIA by increasing the proportion of Treg cells and reducing the proportion of CD8 + T cells.

Objectives: Although various studies have been performed on the function of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in RA, the results were conflicting. Here we were trying to clarify the role of PMN-MDSCs in the pathogenesis of RA and its specific mechanisms. Methods: We detected the frequencies and counts of PMN-MDSCs, TNF- + B cells, and Ki67 + B cells in spleens and inflamed joints of collagen-induced arthritis (CIA) mice using flow cytometry. The pathological role of PMN-MDSCs was examined by anti-Ly6G neutralizing antibodies against PMN-MDSCs or adoptive transfer of PMN-MDSCs. And the modulation of PMN-MDSCs on B cells was conducted by coculture assays, RNA-Seq, RT-qPCR, etc. The mechanism of BAFF regulating B cells was verified through Western Blot and flow cytometry. Results: PMN-MDSCs accumulated in the spleens and joints of CIA mice. PMN-MDSCs depletion could alleviate the arthritis severity, which was accompanied by decreased TNF- secretion and proliferation of B cells. And its adoptive transfer also facilitated disease progress. Furthermore, PMN-MDSCs from CIA mice had higher expression level of BAFF, which regulated TNF- expression, proliferation and apoptosis of B cells in vitro. What’s more, BAFF promoted phosphorylation of BTK/NF-B signaling pathway. And Ibrutinib (BTK inhibitor) could reverse the effect of BAFF on TNF- expression. Conclusions: Our study suggested that PMN-MDSCs enhanced disease severity of CIA and manipulated TNF- expression, proliferation and apoptosis of B cells via BAFF, furthermore, BAFF promoted TNF- expression through BTK/NF-B signaling pathway, which demonstrated a novel pathogenesis of PMN-MDSC in CIA.