Objective: To investigate the immunoregulatory function of bone marrow mesenchymal stem cells (MSCs) on allogeneic B lymphocytes in vitro, and explore its possible mechanisms.
Methods: Human MSCs were isolated from bone marrow and expanded in vitro. The purity of MSCs were identified with the spindle fibroblastic morphology by micro-photograph and the phenotype by flow cytometry. MSCs were irradiated with 20 Gy of gamma ray to abolish proliferative capacity. The change of activated B cells proliferative capability and apoptosis with or without MSCs were examined. The effect of MSCs on activated B cells proliferation was compared between transwell cultures and non-transwell cultures. The IgG, IgA and IgM productions of B cells and the immune molecules expression with or without MSCs were assessed. RESULTS (1) MSCs could not induce the proliferation of B lymphocytes, but could suppress LPS activated B lymphocytes proliferation. (2) With the number of MSCs increased, a dose-dependent inhibitory effect was observed in B cell proliferation. MSCs could not induce B cells apoptosis. The activated B cells proliferation with MSCs in transwell culture was decreased, suggesting that MSCs inhibition of B cells might be mediated both by cell-to-cell contact and soluble factors. (3) MSCs suppressed the IgG, IgA and IgM production of B cells, but not suppressed the immune molecules HLA-DR, CD40, CD80 and CD86 expression.
Conclusion: Bone marrow MSCs can suppress allogeneic B lymphocytes proliferation and its secretion in vitro.