Interleukin-6 (IL-6) is an endogenous chemical which is active in inflammation and in B cell maturation. Besides being an immune protein, it is also a pyrogen, and is responsible for fever in autoimmune, infectious or non-infectious disease. It is produced in the body, wherever there is inflammation, either acute or chronic. It interacts with interleukin-6 receptor alpha to induce transcription of inflammatory gene products.

IL-6 is one of the key proinflammatory cytokines in triggering this response and is almost entirely responsible for inducing fever and the acute phase response in the liver. In life-threatening infections, the IL-6 level is elevated and correlates with the severity of sepsis and death rate. IL-6 levels are also raised in almost all diseases that involve chronic inflammation such as diabetes and rheumatoid arthritis.

Interleukin-6 (IL-6) has been emphasized by reports of elevated circulating as well as intracardiac IL-6 levels in patients with congestive heart failure (CHF). IL-6 may contribute to the progression of myocardial damage and dysfunction in chronic heart failure syndrome resulting from different causes. As the cause of CHF in cardiomyopathy, myocarditis, allograft rejection, and left ventricular assist device (LVADs) conditions, circulating IL-6 levels are associated with the severity of left ventricular dysfunction, and are also strong predictors of subsequent clinical outcomes.