The synthesis of IL-1 receptor antagonist (IL-1ra) by synovial fibroblasts is markedly increased by the cytokines TNF-alpha and IL-1.

The regulation of inhibitors which block the action of IL-1 has significant implications in the control of inflammation. Different modulators of cellular metabolism were studied for their effect on the synthesis of IL-1 receptor antagonist (IL-1ra). Among the different growth factors and cytokines studied, only the inflammatory mediators IL-1 and TNF-alpha and one growth factor, PDGF-BB, were found to significantly increase, in an additive manner, the synthesis and secretion of IL-1ra.