ARG1 and amyotrophic lateral sclerosis: M1 phenotype is the classical activation distinguished by the upregulated expression of not only CD86 but also pro‐inflammatory cytokines causing cell death and tissue damage.31 M2 phenotype is normally characterized by the massive expression of scavenger receptor CD206 and arginase 1 (Arg‐1), together with the elevated release of anti‐inflammatory cytokines.32 In the early stage of ALS, microglia cells are mainly polarized into M2 phenotype, releasing a large number of anti‐inflammatory factors and exerting neuroprotective effect.