Plays a role in M1 macrophage polarization and is required for the proper regulation of gene expression during M1 versus M2 macrophage differentiation (PubMed:29217193). Might play a role in RELA/p65 and STAT1 phosphorylation and nuclear localization upon activation of macrophages (PubMed:29217193). Expressed in the spleen, with expression in T cells, B cells, natural killer cells and natural killer T cells and high expression in monocytes and macrophages. Up-regulated in macrophages upon induction by lipopolysaccharides (LPS) and IFNG. Down-regulation of M1 macrophage marker genes, including Il12a, Il12b, Cxcl9, Cxcl10, Cxcl11, Hif1a and Il23a, and up-regulation of M2 marker genes, including Arg1, Ym1, Msr1 and Ccl17, in M1 macrophages. In bone marrow derived macrophages, impaired induction of M1 macrophage marker gene expression and impaired phosphorylation and nuclear localization of Rela/p65 and Stat1 after LPS and IFNG stimulation and enhanced M2 macrophage marker gene expression after Il4 stimulation. Reduced number of MHC class II- and F4/80-expressing cells within the population of M1 marker-expressing macrophages.