Innate immunity triggers IL-32 expression by fibroblast-like synoviocytes in rheumatoid arthritis.
BACKGROUND
Interleukin-32 (IL-32) is a recently described cytokine that is a strong inducer of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, IL-1β, IL-6, and IL-8. The expression of this cytokine is highly increased in the rheumatoid synovium and correlated with the severity of joint inflammation. Little is known regarding the innate immune-related regulation of IL-32 by fibroblast-like synoviocytes (FLSs). We therefore investigated the effect of innate immune stimulation by ligands of Toll-like receptor (TLR)2, TLR3, and TLR4, and cytokines such as TNF-α and interferon (IFN)-γ, on IL-32 expression by FLSs.


METHODS
FLSs were isolated from patients with rheumatoid arthritis (RA) according to the ACR criteria. Quantitative RT-PCR, confocal analysis, and ELISA were performed to evaluate IL-32 mRNA induction and IL-32 release by FLSs stimulated with TLR2 (BLP), TLR3 (poly I:C), and TLR4 (lipopolysaccharide) ligands, TNF-α and IFN-γ.


RESULTS
TLR2, -3, and -4 ligands as well as IFN-γ and TNF-α induced IL-32 β, γ and δ mRNA expression by RA FLSs. Mature IL-32 was expressed intracellularly and released by cells stimulated with the various activators. The IL-32α isoform was expressed intracellularly in response to TNF-α and poly I:C and not released in culture supernatants. Stimulation of FLS with TNF-α, BLP, lipopolysaccharide, or poly I:C concomitant with IFN-γ increased IL-32 expression compared with stimulation with IFN-γ alone.


CONCLUSIONS
IL-32 synthesis by FLSs is tightly regulated by innate immunity in rheumatoid arthritis. Thus TNF-α, IFN-γ, double-strand RNA, hyaluronic acid, or other damage-associated molecular patterns (DAMPs), highly secreted in synovial tissues of RA patients, might trigger IL-32 secretion by FLSs. IL-32 might therefore represent a relevant therapeutic target in RA.
Alsaleh
Ghada
G
Université de Strasbourg, UFR Sciences Pharmaceutiques, 67401 Illkirch, France. ghada.alsaleh@pharma.u-strasbg.fr
Sparsa
Laetitia
L
Chatelus
Emmanuel
E
Ehlinger
Mathieu
M
Gottenberg
Jacques-Eric
JE
Wachsmann
Dominique
D
Sibilia
Jean
J
D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D004357:Drug Synergism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D015870:Gene Expression / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D007369:Interferon Inducers / Q000276:immunology / Q000494:pharmacology; D007371:Interferon-gamma / Q000276:immunology / Q000494:pharmacology; D007378:Interleukins / Q000235:genetics / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D011070:Poly I-C / Q000276:immunology / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D013583:Synovial Membrane / Q000166:cytology / Q000276:immunology*; D051195:Toll-Like Receptor 2 / Q000276:immunology / Q000378:metabolism; D051196:Toll-Like Receptor 3 / Q000276:immunology / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000494:pharmacology
C496971:IL32 protein, human; D007369:Interferon Inducers; D007378:Interleukins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; C495342:TLR2 protein, human; C495344:TLR3 protein, human; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D011070:Poly I-C