Lupus-Associated Immune Complexes Activate Human Neutrophils in an FcγRIIA-Dependent but TLR-Independent Response.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of autoantibodies against nucleic acids and nucleoproteins. Anti-dsDNA Abs are considered a hallmark of SLE, and previous studies have indicated that nucleic acid-containing immune complexes (ICs) induce B cell and dendritic cell activation in a TLR-dependent process. How ICs containing nucleic acids affect neutrophil function has not been well investigated. In this study, we report that nucleic acid-containing ICs derived from the sera of SLE patients induce human and mouse neutrophil activation through TLR-independent mechanisms. Soluble ICs containing Sm/RNP, an RNA Ag, activate human neutrophils to produce reactive oxygen species (ROS) and IL-8. In contrast, ICs containing DNA have to be immobilized to efficiently activate neutrophils. We found that deleting TLR7 or TLR9, the receptors for RNA and DNA, had no effect on mouse neutrophil activation induced by RNA-containing and immobilized DNA-containing ICs. Binding of ICs are mediated through FcγRIIA and FcγRIIIB. However, neutrophil activation induced by RNA- and DNA-containing ICs requires FcγRIIA, as blocking FcγRIIA inhibited ROS release from neutrophils. RNA-containing ICs induce calcium flux, whereas TLR7/8 ligand R848 do not. Surprisingly, chloroquine inhibits calcium flux induced by RNA-containing ICs, suggesting that this lesser known function of chloroquine is involved in the neutrophil activation induced by ICs. These data indicate the SLE-derived ICs activate neutrophils to release ROS and chemokines in an FcγRIIA-dependent and TLR7- and TLR9-independent manner that likely contributes to local tissue inflammation and damage.

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.

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

Immune activation of fibrosis likely has a crucial role in the pathogenesis of systemic sclerosis (SSc). The aim of this study was to better understand the innate immune regulation and associated IFN- and transforming growth factor-ß (TGFß)-responsive gene expression in SSc skin and dermal fibroblasts, in particular the effect of different Toll-like receptor (TLR) ligands. To better understand the relationship between inflammation and fibrosis in vivo, we developed a murine model for chronic innate immune stimulation. We found that expression of both IFN- and TGFß-responsive genes is increased in SSc skin and SSc fibroblasts when stimulated by TLR ligands. In contrast, cutaneous lupus skin showed much more highly upregulated IFN-responsive and much less highly upregulated TGFß-responsive gene expression. Of the TLRs ligands tested, the TLR3 ligand, polyinosinic/polycytidylic acid (Poly(I:C)), most highly increased fibroblast expression of both IFN- and TGFß-responsive genes as well as TLR3. Chronic subcutaneous immune stimulation by Poly(I:C) stimulated inflammation, and IFN- and TGFß-responsive gene expression. However, in this model, type I IFNs had no apparent role in regulating TGFß activity in the skin. These results suggest that TLR agonists may be important stimuli of dermal fibrosis, which is potentially mediated by TLR3 or other innate immune receptors.

A macrophage marker, Siglec-1, is increased on circulating monocytes in patients with systemic sclerosis and induced by type I interferons and toll-like receptor agonists.

OBJECTIVE: Microarray analyses of peripheral blood leukocytes have shown that patients with systemic lupus erythematosus express increased levels of type I interferon (IFN)-regulated genes. In this study we examined gene expression by peripheral blood mononuclear cells (PBMCs) from patients with systemic sclerosis (SSc) to better understand the dysregulation of the immune system in this disease. METHODS: PBMC gene expression was analyzed by microarray and confirmed by real-time polymerase chain reaction (PCR). Surface protein expression of Siglec-1 was analyzed by flow cytometry in PBMCs from healthy control subjects and patients with SSc, and in control PBMCs that were cultured in vitro with Toll-like receptor (TLR) agonists. RESULTS: SSc patients showed increased expression of a cluster of IFN-regulated genes, including Siglec-1 (CD169, sialoadhesin). This result was verified and extended by real-time PCR, showing that a subset of the SSc patients expressed strikingly increased levels of Siglec-1 messenger RNA (mRNA). Flow cytometry of PBMCs from SSc patients and healthy controls showed increased Siglec-1 surface protein expression, which was restricted to CD14+ monocytes. In vitro studies showed that type I IFN and certain TLR agonists, including TLR-7 and TLR-9, induced Siglec-1 mRNA and protein expression. Moreover, TLR induction of surface Siglec-1 was shown to be type I IFN-dependent. Increased numbers of Siglec-1+ cells were observed by immunohistochemistry in the skin of SSc patients compared with healthy controls. CONCLUSION: Increased expression of Siglec-1 in circulating SSc monocytes and tissue macrophages suggests that type I IFN-mediated activation of monocytes occurs in SSc, possibly through TLR activation of IFN secretion. These observations indicate a potential role for type I IFN-activated monocyte/macrophages in the pathogenesis of SSc.