The formation of adipose tissue could result from abnormal metabolic processes and, at the local level, from chronic inflammatory processes such as those occurring in the synovial cavity in rheumatoid arthritis or osteoarthritis, or the peritoneal cavity in various inflammatory processes of the digestive system. Adipocytes are said to produce many hormones and proinflammatory mediators. So far, however, little attention has been paid to cytokine inhibitory molecules. Based on our observation of high levels of serum interleukin receptor antagonist (IL-1Ra) in obese patients contrasting with decreased levels after gastric bypass surgery, we found white adipose tissue (WAT) in the human system to be the main source of IL-1Ra. IL-10 was also present in WAT. Furthermore, we found that interferon-beta (IFN)-beta was the principal cytokine inducing IL-1Ra in various WAT, such as that present in the synovium. We suggest that in addition to other functions adipose tissue may give rise to a host-defense mechanism against local inflammation and that fibrotic tissue in the vicinity may further induce IL-1Ra in adipocytes via the production of IFN-beta.