Differential effect of IL-1β and TNF-α on the production of IL-6, IL-8 and PGE₂ in fibroblast-like synoviocytes and THP-1 macrophages

Inflammation in the joint of rheumatoid arthritis is a complex immune reaction facilitated by various factors, such as cytokines, cells and hypoxia. Thus, we evaluated their relative capacity to produce proinflammatory mediators in response to IL-1β, TNF-α or IL-17 under hypoxia or normoxia in fibroblast-like synoviocytes (FLSs) and macrophages. The level of IL-6 expression was strongly increased in both FLSs and THP-1 macrophages in response to IL-1β and TNF-α, but the level by TNF-α was less than that by IL-1β. In contrast, the expression of IL-8 in both cell types was strongly stimulated by both IL-1β and TNF-α. In FLSs, PGE₂ production increased only in response to IL-1β; and no effect was observed in THP-1 cells and TNF-α-stimulated FLSs. In addition, the production by IL-17 was extremely low when compared with those induced by IL-1β or TNF-α in FLSs and THP-1 cells. Hypoxia (2% O₂) decreased IL-1β-stimulated production of PGE₂, even though it increased the expression of mRNA and protein of COX-2. These results suggest that IL-1β and TNF-α differentially regulate gene expression in FLSs and macrophages under hypoxia or normoxia.