IL-6 is a helical glycoprotein with a molecular weight from 20 to 30 kD. Under physiologic conditions, the main source of IL-6 are cells of the immune system, vascular endothelial cells, and adipocytes. The concentration of IL-6 in the serum follows a circadian rhythm. IL-6 expression is mainly modulated by the nuclear factor kappa B (NF-KB).
The physiological role of IL-6 has been mostly studied in the context of the acute phase response, although there is growing evidence that IL-6 also plays a central role in the pathogenesis of chronic disease. . In acute inflammation, IL-6 promotes the expansion and activation of T cells and differentiation of B cells, and modulates the synthesis of positive (such as C-reactive protein and fibrinogen) and negative (such as albumin) acute phase reactants. the transition to a chronic inflammatory state is sustained by IL-6 trans signaling.
There is strong evidence that IL-6 serum concentration increases with age. Age-related increments in IL-6 are not explained by differential prevalence of IL-6 gene polymorphisms, while there is evidence that the excessive production or reduced clearance of oxygen free radicals, which stimulate IL-6 production, may be important.