CCL2 and CXCL12 Derived from Mesenchymal Stromal Cells Cooperatively Polarize IL-10+Tissue Macrophages to Mitigate Gut Injury

Mesenchymal stromal cell (MSC)-based therapy for inflammatory diseases involves paracrine and efferocytotic activation of immunosuppressive interleukin-10(+) (IL-10(+)) macrophages. The paracrine pathway for MSC-mediated IL-10(+) macrophage functionality and response to tissue injury is not fully understood. In our present study, clodronate pretreatment of colitic mice confirms the essential role of endogenous macrophages in bone-marrow-derived MSC (BM-MSC)-mediated clinical rescue of dextran sulfate sodium (DSS)-induced colitis. We identify that BM-MSC-secreted chemokine ligand 2 (CCL2) and C-X-C motif chemokine 12 (CXCL12) cooperate as a heterodimer to upregulate IL-10 expression in CCR2(+) macrophages in vitro and that CCL2 expression by MSC is required for IL-10(+) polarization of intestinal and peritoneal resident macrophages in vivo. We observe that tissue macrophage IL-10 polarization in vivo is widespread involving extra-intestinal tissues and secondarily leads to bystander IL-10 expression in intestine-resident B and T cells. In conclusion, the BM-MSCderived chemokine interactome dictates an IL-10(+)-macrophage-amplified anti-inflammatory response in toxic colitis.