Figure 3.

MSCs can modulate macrophage function through several mechanisms. MSCs can induce M2 polarization of monocytes, primed M1 macrophages (stimulated with GM-CSF or thioglycollate) and polarized M1 macrophages (polarized with LPS and/or IFN-γ). MSCs can also inhibit the GM-CSF/IL-4-mediated differentiation of monocytes into immature dendritic cells and prevent the LPS/IFN-γ-mediated polarization into M1 macrophages and instead promote a M2-like macrophage activation state. MSCs use both active (TSG-6, PGE₂, cytokines/growth factors and lactate) and passive (phagocytosis of MSCs by macrophages, transfer of microRNAs and mitochondria to macrophages) mechanisms to modulate macrophage function.