The objective of the study was to investigate the detailed mechanisms of TNF-α-induced cPLA2 expression and to determine whether carbon monoxide releasing molecule-2 (CO-RM2) suppresses TNF-α-induced expression of NF-κB-related proinflammatory genes, including cPLA2, via HO-1 induction in RA synovial fibroblasts (RASFs). This evidence concerns the gene HMOX1 and rheumatoid arthritis.