Inhibition of inducible NO synthase by TH2 cytokines and TGFβ in rheumatoid arthritic synoviocytes:: Effects on nitrosothiol production

The aim of this study was to compare the effects on NO production of IL-4, IL-10, and IL-13 with those of TGF-beta. RA synovial cells were stimulated for 24 h with IL-1beta (1 ng/ml), TNF-alpha (500 pg/ml), IFN-gamma (10(-4)IU/Ml) alone or in combination. Nitrite was determined by the Griess reaction, S-nitrosothiols by fluorescence, and inducible NO synthase UNOS) by immunofluorescence and fluorescence activated cell sorter analysis (FACS). In other experiments, IL-4, IL-10, IL-13, and TGFbeta were used at various concentrations and were added in combination with proinflammatory cytokines. The addition of IL-1beta, TNF-alpha, and IFN-gamma together increased nitrite production: 257.5 +/- 35.8 % and S-nitrosothiol production: 413 +/- 29%, P < 0.001. None of these cytokines added alone had any significant effect. iNOS synthesis increased with NO production. IL-4, IL-10, IL-13, and TGFbeta strongly decreased the NO production caused by the combination of IL-1beta, TNF-alpha, and IFN-gamma. These results demonstrate that stimulated RA synoviocytes produce S-nitrosothiols, bioactive NO. compounds, in similar quantities to nitrite. IL-4, IL-10, IL-13, and TGF-beta decrease NO production by RA synovial cells. The anti-inflammatory properties of these cytokines may thus be due at least in part to their effect on NO metabolism. (C) 2002 Elsevier Science (USA).