Poly(I:C) drives type I IFN- and TGFβ-mediated inflammation and dermal fibrosis simulating altered gene expression in systemic sclerosis

Administration of poly(I:C) improved dermatophagoides farinae-induced atopic dermatitis-like skin lesions in NC/Nga mice by the regulation of Th1/Th2 balance

Atopic dermatitis (AD) is characterized by a chronic and replapsing skin disease with Th2-dominant allergic inflammation. Poly(I:C) has been shown to have immunopotentiator properties, but its effect on AD has not been examined. In this study, the immunomodulatory effects of poly(I:C), using dermatophagoides farinae (Df)-induced AD-like skin lesions in NC/Nga mice, were investigated. The clinical scores were reduced significantly by the treatment with poly(I:C) at 25 and 50 μg/mouse. Histological analysis of the skin also revealed that treatment of poly(I:C) at 25 and 50 μg/mouse significantly reduced the inflammatory cellular infiltrate, including mast cells and eosinophils. Moreover, poly(I:C) increased the level of IFN-γ, a Th1 cytokine, whereas decreasing that of selective Th2 cytokine both in vivo and in vitro. The levels of serum IgE and Th2 chemokines such as eotaxin, TARC, in spleen cells were also reduced by poly(I:C). These results suggest that poly(I:C) inhibit the development of Df-induced AD-like skin lesions in NC/Nga mice through regulation of the Th1/Th2 balance. Therefore, our results indicate that poly(I:C) might be a useful immunomodulatory agent for the treatment of human AD.

Targeting STAT4 in systemic sclerosis: a promising new direction

Evaluation of: Avouac J, Fürnrohr BG, Tomcik M et al. Inactivation of the transcription factor STAT-4 prevents inflammation-driven fibrosis in animal models of systemic sclerosis. Arthritis Rheum. 63(3), 800-809 (2011). STAT4 has been identified as a genetic risk factor for the development of autoimmune diseases including systemic sclerosis. STAT4 regulates Th1 cell development and cell-mediated immunity, but it is not known how it may regulate the development of dermal fibrosis. Using the bleomycin-induced dermal fibrosis model, it has now been demonstrated that STAT4-deficient mice have reduced dermal fibrosis in part via STAT4-dependent alterations in T-cell proliferation and cytokine production. These data stress the importance of STAT4 in autoimmune diseases such as systemic sclerosis and provide an important direction for future research to improve our understanding of systemic sclerosis pathogenesis.

Novel insights on the role of the innate immune system in systemic sclerosis

Over the last several years the involvement of the innate immune system in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE) has become well established. As systemic sclerosis (SSc; scleroderma) shares clinical features and autoantibodies with SLE, investigation has recently focused on the role of innate immunity in SSc. This has been supported by recent genetic studies. However, unlike SLE and other related autoimmune diseases, SSc patients suffer from pathologic fibrosis of skin and internal organs. The fibrotic component of SSc shares several features with syndromes following environmental exposures to agents such as organic solvents, silica dust and bleomycin. Recent work in SSc and these related fibrotic diseases have identified several areas in which innate immunity can stimulate inflammation as well as fibrosis. This article will focus on the recent discoveries identifying a prominent role of cells of the innate immune system, pattern recognition receptors, and activation of dendritic cells in the pathogenesis of SSc.

Understanding fibrosis in systemic sclerosis: shifting paradigms, emerging opportunities

Fibrosis in multiple organs is a prominent pathological finding and distinguishing hallmark of systemic sclerosis (SSc). Findings during the past 5 years have contributed to a more complete understanding of the complex cellular and molecular underpinning of fibrosis in SSc. Fibroblasts, the principal effector cells, are activated in the profibrotic cellular milieu by cytokines and growth factors, developmental pathways, endothelin 1 and thrombin. Innate immune signaling via Toll-like receptors, matrix-generated biomechanical stress signaling via integrins, hypoxia and oxidative stress seem to be implicated in perpetuating the process. Beyond chronic fibroblast activation, fibrosis represents a failure to terminate tissue repair, coupled with an expanded population of mesenchymal cells originating from bone marrow and transdifferentiation of epithelial cells, endothelial cells and pericytes. In addition, studies have identified intrinsic alterations in SSc fibroblasts resulting from epigenetic changes, as well as altered microRNA expression that might underlie the cell-autonomous, persistent activation phenotype of these cells. Precise characterization of the deregulated extracellular and intracellular signaling pathways, mediators and cellular differentiation programs that contribute to fibrosis in SSc will facilitate the development of selective, targeted therapeutic strategies. Effective antifibrotic therapy will ultimately involve novel compounds and repurposing of drugs that are already approved for other indications.

Vascular involvement in systemic sclerosis (scleroderma)

Systemic sclerosis (SSc) is an acquired multiorgan connective tissue disease with variable mortality and morbidity dictated by clinical subset type. The etiology of the basic disease and pathogenesis of the systemic autoimmunity, fibrosis, and fibroproliferative vasculopathy are unknown and debated. In this review, the spectrum of vascular abnormalities and the options currently available to treat the vascular manifestations of SSc are discussed. Also discussed is how the hallmark pathologies (ie, how autoimmunity, vasculopathy, and fibrosis of the disease) might be effected and interconnected with modulatory input from lysophospholipids, sphingosine 1-phosphate, and lysophosphatidic acid.

The role of NK cells in the development of autoantibodies

The systemic lupus erythematosus (Sle1) interval from the NZM2410 mouse strain has been shown to be responsible for high levels of autoantibody production against antinuclear antibodies (ANA) when transferred into C57BL/6 mice. B cells derived from the B6.Sle1 strain are required for the production but help from both T-dependent and independent sources have been documented. Using radiation chimeras constructed in a strain of mice that is chronically depleted of Natural killer (NK) cells, but not NKT cells, we have examined the role of NK cells in the development of ANA in this context. Our results show that in the presence of intact T cell help depletion of NK cells does not affect ANA production. However, when T cell help is compromised, the prevalence of animals producing ANA is significantly decreased suggesting that NK cells can provide help for the T-independent production of ANA. Further experiments provide a possible mechanism for the NK-cell dependence.

Toll-like receptor driven B cell activation in the induction of systemic autoimmunity

Studies over the past decade have demonstrated a key role for pattern recognition receptors in the activation of autoreactive B cells. Self reactive B cells that manage to escape negative selection often express relatively low affinity receptors for self antigens (ignorant B cells), and can only be activated by integrating a relatively weak BCR signal with signals from additional receptors. Members of the toll-like receptor (TLR) gene family, and especially the nucleic acid binding receptors TLR 7, 8 and 9, appear to play a key role in this regard and promote the production of autoantibodies reactive with DNA- or RNA-associated autoantigens. These autoantibodies are able to form immune complexes with soluble or cell-bound ligands, and these immune complexes can in turn activate a second round of proinflammatory cells that further contribute to the autoimmune disease process. Recent data have emerged showing a pathogenic role for TLR7, with an opposing, protective role for TLR9. Targeting these disregulated pathways offers a therapeutic opportunity to treat autoimmune diseases without crippling the entire immune system. Further understanding of the role of specific receptors, cell subsets, and inhibitory signals that govern these TLR-associated pathways will enable future therapeutics to be tailored to specific categories of autoimmune disease.

Toll-like receptors in rheumatic diseases: are we paying a high price for our defense against bugs?

In the last decade Toll-like receptor (TLR) research has led to new insights in the pathogenesis of many rheumatic diseases. In autoimmune diseases like systemic lupus erythematosus, rheumatoid arthritis and systemic sclerosis TLR signaling is likely to be involved in tolerance breakthrough and chronic inflammation via combined Fc gamma receptors and TLR recognition of immune complexes. Furthermore, inflammatory diseases like psoriatic arthritis and gout also show more and more evidence for TLR involvement. In this review we will discuss the involvement of TLR signaling in several rheumatic diseases and stress their similarities and differences based on recent findings.

Toll-like receptor 3 upregulation by type I interferon in healthy and scleroderma dermal fibroblasts

Introduction

Increased levels of genes in the type I interferon (IFN) pathway have been observed in patients with systemic sclerosis (SSc), or scleroderma. How type I IFN regulates the dermal fibroblast and its participation in the development of dermal fibrosis is not known. We hypothesized that one mechanism by which type I IFN may contribute to dermal fibrosis is through upregulation of specific Toll-like receptors (TLRs) on dermal fibroblasts. Therefore, we investigated the regulation of TLR expression on dermal fibroblasts by IFN.

Methods

The expression of TLRs was assessed in cultured dermal fibroblasts from control and SSc patients stimulated with IFNα2. The ability of IFNα2 to regulate TLR-induced interleukin (IL)-6 and CC chemokine ligand 2 production was also assessed. Immunohistochemical analyses were performed to determine whether TLR3 was expressed in skin biopsies in the bleomycin-induced skin fibrosis model and in patients with SSc.

Results

IFNα2 increased TLR3 expression on human dermal fibroblasts, which resulted in enhanced TLR3-induced IL-6 production. SSc fibroblasts have an augmented TLR3 response to IFNα2 relative to control fibroblasts. Pretreatment of fibroblasts with transforming growth factor (TGF)-β increased TLR3 induction by IFNα2, but coincubation of TGF-β did not alter TLR3 induction by IFN. Furthermore, IFNα2 inhibits but does not completely block the induction of connective tissue growth factor and collagen expression by TGF-βin fibroblasts. TLR3 expression was observed in dermal fibroblasts and inflammatory cells from skin biopsies from patients with SSc as well as in the bleomycin-induced skin fibrosis model.

Conclusions

Type I IFNs can increase the inflammatory potential of dermal fibroblasts through the upregulation of TLR3.

dsRNA activation of endothelin-1 and markers of vascular activation in endothelial cells and fibroblasts

BACKGROUND

In patients with systemic sclerosis (SSc), the relationship between innate immune activation, represented by increased expression of interferon (IFN)-regulated genes, and vascular injury/activation, manifest by increased endothelin-1 (ET-1), endothelin converting enzyme-1 (ECE1) and intercellular adhesion molecule-1, is uncertain.

OBJECTIVE

To investigate the potential roles of innate immune ligands in both these pathogenic pathways.

METHODS

The effect of known Toll-like receptor (TLR) ligands was tested in vitro on dermal microvascular and pulmonary arterial endothelial cells, and on dermal fibroblasts cultured from healthy controls and patients with SSc. To test the effect of double-stranded RNA (dsRNA) on vascular activation/injury in vivo, polyinosinic/polycytidylic acid (poly(I:C)) was administered continuously over 7 days by subcutaneous osmotic pump.

RESULTS

dsRNA/poly(I:C), but not other TLR ligands, highly stimulated ET-1 protein and mRNA (EDN1), as well as intercellular adhesion molecule-1 (ICAM-1) and IFN-regulated MX2, by endothelial cells and dermal fibroblasts. Poly(I:C) induced EDN1, ECE1, and ICAM-1 mRNA expression in poly(I:C) treated skin. Poly(I:C)-induced EDN1, ECE1 and MX2 was not blocked in mice with the type I IFN receptor deleted. However, poly(I:C)-induced EDN1 and ECE1, but not poly(I:C)-induced ICAM-1 expression was blocked in mice with the TLR3 signalling protein TRIF/TICAM-1 deleted.

CONCLUSION

Together these data show that the dsRNA can regulate genes associated with vascular activation, as seen in SSc, that type I IFNs do not mediate these effects, and that EDN1 and ECE1 but not ICAM-1 activation is mediated by TLR3.