The role of macrophages in the acute-phase response: SAA inducer is closely related to lymphocyte activating factor and endogenous pyrogen

Abstract

An increase in the concentration of the acute-phase reactant, serum amyloid A (SAA), following endotoxin treatment, is a consequence of the action of lipopolysaccharide (LPS) on macrophages to produce a monokine, the SAA inducer, which in turn, triggers SAA synthesis by hepatocytes. We have found that murine SAA inducer is closely related, if not identical, to murine lymphocyte activating factor (LAF), otherwise known as Interleukin 1 (IL 1). Furthermore, both rabbit endogenous pryrogen (EP), which is believed to be identical to LAF (IL 1), and human LAF (IL 1), induced elevated SAA concentrations in C3H/HeJ mice. Antiserum previously shown to block both pyrogenic and thymocyte proliferating activities of the species of rabbit EP exhibiting an isoelectric point of pH 7.3 (EP 7), also blocked the SAA inducing activity of EP7. Phenylglyoxal treatment of highly purified murine LAF (IL 1) abrogated both thymocyte proliferating activity and the SAA inducing activity. These studies support and extend previous reports suggesting that within 2 hr of an inflammatory stimulus, macrophages produce a monokine that acts systemically to alter body temperature, activate T cells, and induce hepatic protein synthesis of acute-phase reactants.