HMOX1 and rheumatoid arthritis: HO-1 protein is expressed in synovial tissues of RA patients [6] and its presence in synovial fluid may be a marker of joint inflammation [7] Nevertheless, treatment of RA patients with tumor necrosis factor α (TNF-α) antagonists may block the TNF-α-dependent suppression of HO-1 expression in peripheral blood cells, resulting in amelioration of inflammation [8].