Elevated levels of hyaluronan are associated with numerous inflammatory diseases including inflammatory bowel disease. The purpose of this study was to determine whether a cause and effect relationship might exist between proinflammatory cytokines, interleukin-1 (IL-1), tumor necrosis factor- (TNF-), interferon- (IFN-) or transforming growth factor- (TGF-) and hyaluronan expression in human jejunum-derived mesenchymal cells (JDMC) and if so, to identify possible mechanisms involved in the induction of hyaluronan expression . TGF-, TNF-, and IFN- had little or no effect on hyaluronan production by these cells. Treatment with IL-1 induced an approximate 30-fold increase in the levels of hyaluronan in the medium of human jejunum-derived mesenchymal cells. Ribonuclease protection analysis revealed that steady-state transcript levels for hyaluronan synthase 2 (HAS2) were present at very low levels in untreated cells but increased as much as 18-fold in the presence of IL-1. Hyaluronan synthase 3 (HAS3) transcript levels were also increased slightly by exposure of these cells to IL-1. Expression of hyaluronan synthase 1 transcripts was not detected under any condition in these cells. IL-1 induction of hyaluronan expression was inhibited in cells transfected with siRNA corresponding to HAS2 transcripts. Inhibitors of the p38 and ERK1/2 mitogen activated pathways, but not JNK/SAPK, blocked the IL-1-mediated induction of hyaluronan expression and the increase in HAS2 transcript expression. These results suggest that IL-1 induction of HAS2 expression involves multiple signaling pathways that act in concert thus leading to an increase in expression of hyaluronan by jejunum-derived mesenchymal cells.