Impaired B Cell Inhibition by Lupus Bone Marrow Mesenchymal Stem Cells Is Caused by Reduced CCL2 Expression

Mesenchymal stem cells (MSC) from healthy human and normal mice can inhibit normal B cell proliferation, differentiation, and Ab secretion in vitro. However, it remains unknown whether MSC from lupus-like mice and patients with systemic lupus erythematosus (SLE) exhibit the same immunoregulatory activity as normal MSC for B cell inhibition and, if not, what the underlying molecular mechanism would be. In this study, we showed that bone marrow-derived MSCs from lupus-like mice and SLE patients had an impairment in suppressing normal B cell proliferation and differentiation, which was caused by the reduction of CCL2 levels. Knockdown of CCL2 in normal MSC damaged their suppressive capacity for B cells. Conversely, overexpression of CCL2 in lupus MSCs restored their immunoregulatory ability for B cells in vitro and ameliorated the pathology of lupus nephritis and serological changes in MRL/lpr mice in vivo. Mechanistically, MSC-mediated B cell inhibition was dependent on matrix metalloproteinase proteolytic processing of CCL2. These findings reveal a novel function of CCL2 in B cell regulation by MSCs and suggest that CCL2 manipulation on MSCs may serve as a potential pathway for developing the more effective MSC-based therapy in autoimmune diseases associated with B cell activation, such as SLE.