TNF and rheumatoid arthritis: The IPFP is a special type of connective tissue rich in fat cells, fibroblasts, and adipose-derived stem cells, which secrete a large number of anti-inflammatory factors, such as leptin and adiponectin, that further increase the proteoglycan synthesis and decrease secretion of tumor necrosis factor alpha and interleukin-1 in RA [42, 43].