HMOX1 and rheumatoid arthritis: Although anti-inflammatory components, such as HO-1 are also induced in the synovial joints, the levels of HO-1 are shown to decline with the advanced immunopathogenesis of RA (Kitamura et al., 2011; May et al., 2018), which is presumably moderated by the RA-driven proinflammatory circadian responses (Lee et al., 2017).