Macrophage migration inhibitory factor (MIF) supports mitochondrial metabolism during inflammatory macrophage activation

Macrophage migration inhibitory factor (MIF) is a pleiotropic proinflammatory cytokine implicated in inflammatory diseases in which macrophages critically shape immune outcomes. Although MIF has been linked to macrophage polarization, its bioenergetic contributions remain insufficiently defined. Here, we investigated how MIF regulates mitochondrial function in bone marrow-derived macrophages (BMDMs) from wild-type (WT) and MIF-knockout ( Mif −/− ) mice under nonpolarized (M0), recombinant MIF-treated (M0 + rMIF), and M1 or M2 polarization conditions. Compared with M1 WT macrophages, M1 Mif −/− macrophages exhibit reduced production of reactive oxygen species (ROS), superoxide (O 2 •̶ ), and nitric oxide (NO), accompanied by decreased mitochondrial membrane potential (MMP) and impaired oxidative phosphorylation (OXPHOS). In contrast, M2 Mif −/− macrophages exhibited only modest reductions in arginase activity and mitochondrial parameters. Together, these findings indicate that endogenous MIF is essential for maintaining mitochondrial bioenergetic competence during inflammatory M1 activation, whereas M2 differentiation is largely preserved. This phenotype-dependent regulation highlights a key role for MIF in shaping macrophage activation pathways and macrophage fate during inflammatory responses.