DNA and histone methylation, including TBX5 (Karouzakis et al., 2014), FOXP3 (Kennedy et al., 2014), AHR (Toth et al., 2019), HKMT (Araki et al., 2018), and H3K4me3 (Araki et al., 2016), affect the proliferation, migration, apoptosis, and inflammation of immune cells, which explains the pathogenesis of RA. Here, FOXP3 is linked to rheumatoid arthritis.