title: Tissue-specific regulation of IL-6 production by IL-4. Differential effects of IL-4 on nuclear factor-kappa B activity in monocytes and fibroblasts.
abstract: IL-4 inhibits production of certain proinflammatory cytokines, including IL-1 beta, TNF-alpha, and IL-6, by activated monocytes. Although monocytes are a major source of IL-6, other cell types such as fibroblasts and endothelial cells can also express this cytokine. To determine whether IL-4 inhibits IL-6 expression in non-hemopoietic cells, we investigated the effects of IL-4 on IL-6 production in both primary human fibroblasts and fibroblast lines. Rheumatoid synovial fibroblasts were evaluated in these studies because, like monocytes, they produce high levels of IL-6 when stimulated with IL-1. Although peripheral blood monocytes did not constitutively express IL-6 mRNA or protein, stimulation with IL-1 or LPS induced de novo IL-6 expression in these cells. In contrast, synovial fibroblasts displayed a significant basal level of IL-6 production, which was markedly increased after stimulation with IL-1. IL-4 suppressed IL-6 expression in monocytes, but did not inhibit IL-6 production in synovial fibroblasts. The inability of IL-4 to suppress IL-6 synthesis in rheumatoid synovial fibroblasts was not caused by a lack of IL-4R and was not unique to these cells because IL-4 also failed to inhibit IL-6 production in normal fibroblast lines derived from other tissues. Inhibition of IL-6 production by IL-4 in monocytes was associated with decreased nuclear NF-kappa B levels. However, IL-4 does not globally suppress the activity of all DNA-binding proteins because IL-4 treatment did not reduce the levels of NF-IL-6 or NF-IL-1 beta B in the same cells. Because NF-kappa B activation is required for transcription of many cytokine genes, including IL-6, the ability of IL-4 to suppress NF-kappa B activity in monocytes suggests a potential mechanism by which this molecule may inhibit the expression of multiple cytokines.
authors.affiliation: Division of Cytokine Biology, FDA, Bethesda, MD 20892.
authors.forename: R P
authors.initials: RP
authors.lastname: Donnelly
authors.forename: L J
authors.initials: LJ
authors.lastname: Crofford
authors.forename: S L
authors.initials: SL
authors.lastname: Freeman
authors.forename: J
authors.initials: J
authors.lastname: Buras
authors.forename: E
authors.initials: E
authors.lastname: Remmers
authors.forename: R L
authors.initials: RL
authors.lastname: Wilder
authors.forename: M J
authors.initials: MJ
authors.lastname: Fenton
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D005347:Fibroblasts / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D016328:NF-kappa B / Q000032:analysis*; D009928:Organ Specificity; D013583:Synovial Membrane / Q000166:cytology / Q000276:immunology / Q000378:metabolism
chemical_list: D007375:Interleukin-1; D015850:Interleukin-6; D016328:NF-kappa B; D015847:Interleukin-4