IL-6 responds to tissue injury. IL-6 is synthesized and secreted by many different types of cells in addition to adipocytes including immune cells, fibroblasts, endothelial cells, and skeletal muscle cells.
IL-6 is increased in obesity and insulin resistance. Individuals with elevated levels are at higher risk for type 2 diabetes and myocardial infarction. Similar to TNF-a, IL-6 increases NEFA release and reduces adiponectin secretion. IL-6 increases insulin resistance by inhibiting insulin receptor signal transduction in liver cells. It also increases other inflammatory cytokines, interleukin-1 (IL-1) and TNF-a, and stimulates the liver to produce C-reactive protein (CRP), an important protein marker of inflammation.