INTERLEUKIN (IL)-10 INHIBITS NUCLEAR FACTOR KAPPA-B (NF-KAPPA-B) ACTIVATION IN HUMAN MONOCYTES - IL-10 AND IL-4 SUPPRESS CYTOKINE SYNTHESISBY DIFFERENT MECHANISMS

Our previous studies in human monocytes have demonstrated that interle ukin (IL)-10 inhibits lipopolysaccharide (LPS)-stimulated production o f inflammatory cytokines, lL-1 beta, IL-6, IL-8, and tumor necrosis fa ctor (TNF)-alpha by blocking gene transcription. Using electrophoretic mobility shift assays (EMSA), we now show that, in monocytes stimulat ed with LPS or TNF alpha, IL-10 inhibits nuclear localization of nucle ar factor kappa B (NF kappa B), a transcription factor involved in the expression of inflammatory cytokine genes. Several other transcriptio n factors including NF-IL-6, AP-1, AP-2, GR, CREB, Oct-1, and Sp-1 are not affected by IL-10, This selective inhibition by IL-10 of NF kappa B activation occurs rapidly and in a dose-dependent manner and correl ates well with IL-10's cytokine synthesis inhibitory activity in terms of both kinetics and dose responsiveness. Furthermore, compounds such as tosylphenylalanyl chloromethyl ketone and pyrrolidinedithiocarbama te that are known to selectively inhibit NF kappa B activation block c ytokine gene transcription in LPS-stimulated monocytes. Taken together , these results suggest that inhibition of NF kappa B activation may b e an important mechanism for IL-10 supression of cytokine gene transcr iption in human monocytes. IL-4, another cytokine that inhibits cytoki ne mRNA accumulation in monocytes, shows little inhibitory effect on L PS-induced NF kappa B activation. Further examination reveals that, un like IL-10, IL-4 enhances mRNA degradation and does not suppress cytok ine gene transcription. These data indicate that IL-10 and IL-4 inhibi t cytokine production by different mechanisms.