REGULATION OF GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR PRODUCTION BY HUMAN ARTICULAR CHONDROCYTES - INDUCTION BY BOTH TUMOR-NECROSIS-FACTOR-ALPHA AND INTERLEUKIN-1, DOWN-REGULATION BY TRANSFORMING GROWTH-FACTOR-BETA AND UP-REGULATION BY FIBROBLAST GROWTH-FACTOR

Objective. To study the regulation of granulocyte macrophage colony st imulating factor (GM-CSF) production by human articular chondrocytes w hich may contribute to the local GM-CSF production encountered in rheu matoid joints. This growth factor induces human macrophages to migrate and proliferate, improves their accessory function and increases the expression of HLA-DR antigens on macrophages and macrophage-like synov iocytes. Methods. GM-CSF was assayed by ELISA and a bioassay in cell a nd organ culture supernatants from human articular chondrocytes, by in situ hybridization, Northern blot analysis and affinity chromatograph y. Results. Both interleukin 1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) synergistically or additively stimulated chondrocytes to p roduce significant amounts of immunoreactive and bioactive GM-CSF with maximum values of 2928 pg/ml (p < 0.0001 both for IL-1 and/or TNF-alp ha vs baseline). Affinity chromatography using specific monoclonal ant ibodies for human GM-CSF resulted in the purification of a chondrocyte derived 22-23 kDa protein. In situ hybridization demonstrated that th e number of chondrocytes that expressed GM-CSF mRNA correlated well to the amount of GM-CSF secreted into the cultures. Transforming growth factor beta (TGF-beta) and to a lesser extent interferon-gamma (IFN-ga mma) were able to decrease GM-CSF production induced by IL-1 and/or TN F-alpha. In contrast, basic fibroblast growth factor (FGF) in combinat ion with IL-1 strongly increased GM-CSF secretion up to 8.5-fold. IFN- gamma, IL-6, TGF-beta, bFGF and IL-8 given alone failed to induce chon drocytes to produce GM-CSF. Steroids and low concentrations of cycloox ygenase inhibitors in general suppressed cytokine induced GM-CSF produ ction. Conclusion. Our data demonstrate that both proinflammatory cyto kines IL-1 and TNF-alpha induce an immunoreactive and biologically act ive GM-CSF by human articular chondrocytes that appears to be downregu lated by TGF-beta and upregulated by FGF. GM-CSF produced locally by c artilage cells may be an important cytokine involved in the activation and proliferation of pannus cells, that can be modulated by interacti ons with cytokines present in the inflamed joints, thus possibly contr ibuting to the chronic infiltration and destruction of cartilage in in flammatory joint diseases.