TNF and rheumatoid arthritis: Data analysis using clustering revealed two distinct RA subgroups associated with increased expression levels of inflammation-related genes [compared with osteoarthritis (OA) control tissue] involved in the tumor necrosis factor TNF-activated interferon regulatory factor (IRF1)- interferon (IFN)- signal transducer and activator of transcription 1 (STAT1)- pathway (34).