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IL-32γ and Streptococcus pyogenes cell wall fragments synergise for IL-1-dependent destructive arthritis via upregulation of TLR-2 and NOD2


Objective To investigate the potential synergism between interleukin (IL) 32γ and Streptococcus pyogenes cell wall (SCW) fragments in the development of destructive arthritis.

Methods An adenoviral vector encoding human IL-32γ (AdIL-32γ) was constructed and validated in HeLa cells. Fibroblast-like synoviocytes (FLS) were transduced with AdIL-32γ and stimulated with Toll-like receptor 2 (TLR-2) and nucleotide oligomerisation domain (NOD) 2 ligands. Expression levels of several proinflammatory cytokines, chemokines, matrix degrading enzymes, TLR-2 and NOD2 were measured by quantitative real-time PCR. Furthermore, IL-6 and CXCL8 protein levels were determined. In-vivo synergy between IL-32γ and SCW was studied by intra-articular injection of AdIL-32γ in C57Bl/6 mice followed by SCW injection. The contribution of endogenous IL-1 was assessed in mice deficient for both IL-1α and IL-1β.

Results IL-32γ synergise with TLR-2/NOD2 ligands to induce proinflammatory cytokines, chemokines and matrix degrading enzymes in AdIL-32γ-transduced FLS. In mice, AdIL-32γ transduction followed by the injection of SCW displayed aggravated joint inflammation and cartilage destruction. However, IL-1-deficient mice were protected against IL-32γ/SCW-induced joint changes, indicating a requirement for IL-1 in downstream events triggered by IL-32γ plus SCW. To elucidate the synergistic mechanism, the authors investigated the expression of two pattern recognition receptors involved in sensing SCW fragments. TLR-2 and NOD2 receptor expression was enhanced by IL-32γ and Pam3Cys/muramyl dipeptide stimulation in FLS.

Conclusions Here the authors show that IL-32γ aggravates SCW-induced arthritis by the upregulation of TLR-2/NOD2 expression and promotes severe joint erosion in an IL-1-dependent fashion. Targeting of IL-32γ may provide a novel therapy to prevent destructive arthritis.

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