TLR4-mediated IL-12 production enhances IFN-? and IL-1? production, which inhibits TGF-? production and promotes antibody-induced joint inflammation.

ABSTRACT:

Introduction

Toll-like receptor (TLR)4 promotes joint inflammation in mice. Despite that several studies report a functional link between TLR4 and interleukin-(IL-)1? in arthritis, TLR4-mediated regulation of the complicated cytokine network in arthritis is poorly understood. To address this, we investigated the mechanisms by which TLR4 regulates the cytokine network in antibody-induced arthritis.

Methods

To induce arthritis, we injected mice with K/BxN serum. TLR4-mediated pathogenesis in antibody-induced arthritis was explored by measuring joint inflammation, cytokine levels and histological alteration.

Results

Compared to wild type (WT) mice, TLR4-/- mice showed attenuated arthritis and low interferon (IFN)-?, IL-12p35 and IL-1? transcript levels in the joints, but high transforming growth factor (TGF)-? expression. Injection of lipopolysaccharide (LPS) enhanced arthritis and exaggerated joint cytokine alterations in WT, but not TLR4-/- or IL-12p35-/- mice. Moreover, STAT4 phosphorylation in joint cells and intracellular IL-12p35 expression in macrophages, mast cells and Gr-1+ cells were detected in WT mice with arthritis and enhanced by LPS injection. Therefore, IL-12p35 appears to act downstream of TLR4 in antibody-induced arthritis. TLR4-mediated IL-12 production enhanced IFN-? and IL-1? production via T-bet and pro-IL-1? production. Recombinant IL-12, IFN-? and IL-1? administration restored arthritis, but reduced joint TGF-? levels in TLR4-/- mice. Moreover, a TGF-? blockade restored arthritis in TLR4-/- mice. Adoptive transfer of TLR4-deficient macrophages and mast cells minimally altered joint inflammation and cytokine levels in macrophage- and mast cell-depleted WT mice, respectively, whereas transfer of WT macrophages or mast cells restored joint inflammation and cytokine expression. Gr-1+ cell-depleted splenocytes partially restored arthritis in TLR4-/- mice.

Conclusion

TLR4-mediated IL-12 production by joint macrophages, mast cells and Gr-1+ cells enhances IFN-? and IL-1? production, which suppresses TGF-? production, thereby promoting antibody-induced arthritis.

SUBMITTER: Kim HS 

PROVIDER: S-EPMC3580522 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature