CCL2 and colitis: In this mechanism, FAS-modulated monocyte chemotactic protein 1 (MCP-1) secreted by MSCs can recruit the T cells for FASL-mediated apoptosis, while the apoptotic T cells further stimulate macrophages to express high levels of TGFβ leading to upregulation of CD4(+)CD25(+)Foxp3(+) Treg cells and, finally, an immune tolerance that can accelerate the recovery of colitis [32,33].