Interleukin (IL)-4, which exhibits potent anti-inflammatory activities, is of potential therapeutic value in destructive arthropathies. To further define the response of human joint cells to IL-4, we analyzed the ability of this cytokine to modulate the effects of IL-1beta and growth factors. Freshly isolated chondrocytes, dedifferentiated chondrocytes, and synoviocytes were treated with IL-4 before determination of nitric oxide (NO) and collagenase production in response to IL-1beta, or before proliferation assays in presence of IL-1beta, platelet-derived growth factor (PDGF), or transforming growth factor (TGF)-beta. IL-4 downregulated IL-1beta induced NO production in dedifferentiated chondrocytes and inhibited IL-1beta induced collagenase release, as well as IL-1beta and growth factor induced proliferation in dedifferentiated chondrocytes and synoviocytes. In contrast, IL-4 had no effect in freshly isolated primary chondrocytes and in cartilage explants. The lack of response to IL-4 in primary chondrocytes was associated with impaired signal transduction, as indicated by markedly decreased IL-4 dependent tyrosine phosphorylation of signal transducer and activator of transcription (STAT)-6. It also correlated with differences in the expression pattern of IL-4 receptor (IL-4R) subunits during chondrocyte dedifferentiation. Indeed, whereas the IL-4Ralpha and IL-13Ralpha' subunits were expressed in all cell types, expression of the common receptor gamma chain was restricted to freshly isolated chondrocytes. In conclusion, IL-4 downregulated IL-1beta-induced catabolic events and cell proliferation in dedifferentiated chondrocytes and synoviocytes, but had no effects in freshly isolated chondrocytes. The difference in IL-4 responsiveness between primary and dedifferentiated chondrocytes correlated with changes in proximal signaling events and in the expression pattern of IL-4R subunits during cell dedifferentiation.
Copyright 2002 Wiley-Liss, Inc.