Scheme of the relationship between chronic inflammation, acute-phase proteins and homeostasis of cytokines. The liver produces both apolipoprotein (apo) A-I and serum amyloid A (SAA). IL-1β and TNF-α differentially regulate the production of acute-phase proteins by increasing the production of SAA (a proinflammatory factor) and decreasing that of apo A-I (an anti-inflammatory factor). The decreased level of apo A-I results in a better activation of monocyte-macrophages (Mφ) by direct contact with stimulated T lymphocytes (sTL), enhancing the production of IL-1 and TNF. The increased levels of SAA result in the substitution of apo A-I by SAA on high-density lipoprotein (HDL), and SAA–HDL further stimulates the production of cytokines by Mφ.