Exosomes Derived From BMMSCs Promote B10 Cell Differentiation but Not IL-10 Production

The role of IL-10-producing regulatory B cells in inflammatory diseases has recently gained substantial attention. Here, we evaluated the function of mouse bone marrow mesenchymal stem cell-derived exosomes (BMMSC-Exos) and their effect on B-cell differentiation. This study aimed to establish an association between BMMSC-Exos and purified B cells and further explored the anti-inflammatory effect of B10 cells. The expression of inflammatory factors, such as IL-1β, TNF-α, and bone metabolism-related factors, including RANKL, OPG, and secreted IL-10, was investigated by RT-qPCR and ELISA. Populations of CD1d^highCD5⁺ B cells were analyzed by flow cytometry and immunofluorescence. Cell viability was assessed by CCK8 assay. The results showed that when B cells were separated from BMMSCs by Transwell, IL-1β, TNF-α, and RANKL were downregulated, whereas IL-10, OPG/RANKL, and CD1d^highCD5⁺ Breg proportion were upregulated in the cocultured groups. Conversely, when B cells were cultured with BMMSC-Exos, increasing concentrations of exosomes increased the proportion of CD1d^highCD5⁺ and IL-10⁺CD45⁺ Bregs; however, the secretion of both pro-inflammatory cytokines and IL-10 were decreased. We found that BMMSC-Exos induce the differentiation of B cells toward the CD1d^highCD5⁺ and IL-10⁺CD45⁺ Breg phenotype but cannot increase the secretion of IL-10 in vitro.