Suppression of IL-2-induced SAA gene expression in mice by the administration of an IL-1 receptor antagonist.

The hepatic acute phase response induced by the administration of interleukin (IL)-2 is most likely mediated by secondary cytokines. In this investigation, we examined the role of endogenous IL-1 in the synthesis of the hepatic acute phase protein serum amyloid A (SAA) during IL-2 treatment. The injection of IL-2 induced SAA gene expression in the liver. The concurrent administration of an IL-1 receptor antagonist (IL-1RA) markedly reduced hepatic SAA mRNA levels and, to a lesser extent, SAA protein levels in the serum. Although IL-1 is an inducer of IL-6 production, the administration of the IL-1RA had no effect on circulating IL-6 levels in IL-2-treated mice. These findings suggest that the production of IL-1 is an important factor in the induction of SAA mRNA in mice undergoing immunotherapy with IL-2.