Irgm1 is required for the inflammatory function of M1 macrophage in early experimental autoimmune encephalomyelitis

The classically activated (M1) macrophage has been shown to play an indispensable role in experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). However, most studies focus on the effect of macrophage on CNS demyelination of EAE; whether the M1 macrophage participates in early EAE and the molecular mechanism underlying remains unclear. Here, we showed that the immunity-related GTPase family member 1 (Irgm1), also known as LRG-47, was expressed in M1 macrophages of draining lymph nodes (dLNs) from C57BL/6 mice with early EAE, and the IRGM1 heterozygote substantially reduced M1 macrophage accumulation in dLNs and spleen of the primary EAE stage. In vitro silence of IRGM1 in M1 macrophages impaired NOS2 expression and inflammatory cytokine release. We also found that IRGM1 knockout (Irgm1(-/-)) in M1 macrophages increased Akt activation but attenuated NF-kappa B p65 activation, which may reveal Irgm1-mediated mechanisms of action. Interestingly, macrophage depletion in vivo inhibited Th1/Th17 differentiation in the spleen and promoted regulatory T cell (T-reg) polarization in dLNs at 7 d postimmunization (dpi). Moreover, we observed that M1 macrophages in vitro promoted Th1/Th17 differentiation, which was reversed by treatment with IRGM1 small interfering RNA (siRNA), anti-TNF-alpha, or anti-IL-1 beta mAb. These results suggest that the M1 macrophage may promote Th1/Th17 cell differentiation during the early EAE, and the proinflammatory function of M1 cells requires Irgm1.