Interleukin-6 (IL-6) is a pro-inflammatory cytokine produced by many cell types including macrophages, monocytes, T cells, and adipose tissue. It is one of the most important mediators of the acute phase response, stimulating the liver to produce acute phase proteins including CRP and fibrinogen. IL-6 also plays central roles in immune regulation, haematopoiesis, and metabolic signalling.

IL-6 is now recognised as a key driver of chronic low-grade inflammation associated with obesity, metabolic syndrome, and cardiovascular disease. Visceral fat (abdominal fat) produces large amounts of IL-6, linking excess adiposity directly to systemic inflammation. IL-6 inhibition has become a major therapeutic target in autoimmune conditions (tocilizumab) and cytokine storm syndromes.