Systemic lupus erythematosus: a matter of life and death

Active haematological manifestations of systemic lupus erythematosus lupus are associated with a high rate of in-hospital mortality

The aim of this study was to estimate the impact of the haematological manifestations of systemic lupus erythematosus (SLE) on mortality in hospitalized patients. For that purpose a case-control study of hospitalized patients in a medical referral centre from January 2009 to December 2014 was performed. For analysis, patients hospitalized for any haematological activity of SLE ( n = 103) were compared with patients hospitalized for other manifestations of SLE activity or complications of treatment ( n = 206). Taking as a variable outcome hospital death, an analysis of potential associated factors was performed. The most common haematological manifestation was thrombocytopenia (63.1%), followed by haemolytic anaemia (30%) and neutropenia (25.2%). In the group of haematological manifestations, 17 (16.5%) deaths were observed compared to 10 (4.8%) deaths in the control group ( P < 0.001). The causes of death were similar in both groups. In the analysis of the variables, it was found that only haematological manifestations were associated with intra-hospital death (odds ratio 3.87, 95% confidence interval 1.8-88, P < 0.001). Our study suggests that apparently any manifestation of haematological activity of SLE is associated with poor prognosis and contributes to increased hospital mortality.

NKG2D ligand overexpression in lupus nephritis correlates with increased NK cell activity and differentiation in kidneys but not in the periphery

NK cells are a major component of the immune system, and alterations in their activity are correlated with various autoimmune diseases. In the present work, we observed an increased expression of the NKG2D ligand MICA in SLE patients' kidneys but not healthy subjects. We also show glomerulus-specific expression of the NKG2D ligands Rae-1 and Mult-1 in various murine SLE models, which correlated with a higher number of glomerular-infiltrating NK cells. As the role of NK cells in the immunopathogenesis of SLE is poorly understood, we explored NK cell differentiation and activity in tissues and organs in SLE-prone murine models by use of diseased and prediseased MRL/MpJ and MRL/lpr mice. We report here that phenotypically iNK cells accumulate only in the spleen but not in BM or kidneys of diseased mice. Infiltrating NK cells in kidneys undergoing a lupus nephritic process showed a more mature, activated phenotype compared with kidney, as well as peripheral NK cells from prediseased mice, as determined by IFN-γ and STAT5 analysis. These findings and the presence of glomerulus-specific NKG2D ligands in lupus-prone mice identify a role for NK cells and NKG2D ligands in the lupus nephritic process, which could aid in understanding their role in human SLE.

Serum progranulin levels are elevated in patients with systemic lupus erythematosus, reflecting disease activity

INTRODUCTION

Progranulin (PGRN) is the precursor of granulin (GRN), a soluble cofactor for toll-like receptor 9 (TLR9) signaling evoked by oligonucleotide (CpG)-DNA. Because TLR9 signaling plays an important role in systemic lupus erythematosus (SLE), we investigated whether PGRN is involved in the pathogenesis of SLE.

METHODS

We measured concentrations of serum PGRN and interleukin-6 (IL-6) with enzyme-linked immunosorbent assay (ELISA) in patients with SLE (n = 68) and in healthy controls (n = 60). We assessed the correlation between the serum PGRN levels and established disease-activity indexes. The sera from the patients with high PGRN titers (>80 ng/ml) at the initial evaluation were reevaluated after the disease was ameliorated by treatment. We also measured the IL-6 concentration secreted by peripheral blood mononuclear cells (PBMCs) incubated with (a) oligonucleotide (CpG-B) in the presence or absence of recombinant human PGRN (rhPGRN); and (b) lupus sera in the presence or absence of a neutralizing anti-PGRN antibody.

RESULTS

Serum PGRN levels were significantly higher in SLE patients than healthy controls. Their levels were significantly associated with activity of clinical symptoms. They also significantly correlated with values of clinical parameters, including the SLE Disease Activity Index and anti-double-stranded DNA antibody titers, and inversely with CH50, C3, and C4 levels. Moreover, serum PGRN levels significantly decreased after successful treatment of SLE. The rhPGRN significantly upregulated the production of IL-6 by PBMCs stimulated with CpG-B. Patients' sera stimulated production of IL-6 from PBMCs, which was significantly impaired by neutralization of PGRN. The serum PGRN levels significantly correlated with the serum IL-6 levels.

CONCLUSIONS

Serum PGRN could be a useful biomarker for disease activity of SLE. PGRN may be involved in the pathogenesis of SLE partly by enhancing the TLR9 signaling.

Sterile inflammation of endothelial cell-derived apoptotic bodies is mediated by interleukin-1α

Sterile inflammation resulting from cell death is due to the release of cell contents normally inactive and sequestered within the cell; fragments of cell membranes from dying cells also contribute to sterile inflammation. Endothelial cells undergoing stress-induced apoptosis release membrane microparticles, which become vehicles for proinflammatory signals. Here, we show that stress-activated endothelial cells release two distinct populations of particles: One population consists of membrane microparticles (<1 μm, annexin V positive without DNA and no histones) and another larger (1-3 μm) apoptotic body-like particles containing nuclear fragments and histones, representing apoptotic bodies. Contrary to present concepts, endothelial microparticles do not contain IL-1α and do not induce neutrophilic chemokines in vitro. In contrast, the large apoptotic bodies contain the full-length IL-1α precursor and the processed mature form. In vitro, these apoptotic bodies induce monocyte chemotactic protein-1 and IL-8 chemokine secretion in an IL-1α-dependent but IL-1β-independent fashion. Injection of these apoptotic bodies into the peritoneal cavity of mice induces elevated serum neutrophil-inducing chemokines, which was prevented by cotreatment with the IL-1 receptor antagonist. Consistently, injection of these large apoptotic bodies into the peritoneal cavity induced a neutrophilic infiltration that was prevented by IL-1 blockade. Although apoptosis is ordinarily considered noninflammatory, these data demonstrate that nonphagocytosed endothelial apoptotic bodies are inflammatory, providing a vehicle for IL-1α and, therefore, constitute a unique mechanism for sterile inflammation.

The type I interferon system in the etiopathogenesis of autoimmune diseases

Many patients with systemic autoimmune diseases have signs of a continuous production of type I interferon (IFN) and display an increased expression of IFN-α-regulated genes. The reason for the on-going IFN-α synthesis in these patients seems to be an activation of plasmacytoid dendritic cells (pDCs) by immune complexes (ICs), consisting of autoantibodies in combination with DNA or RNA-containing autoantigens. Such interferogenic ICs are internalized via the FcγRIIa expressed on pDCs, reach the endosome, and stimulate Toll-like receptor (TLR)-7 or -9, which subsequently leads to IFN-α gene transcription. Variants of genes involved in both the IFN-α synthesis and response have been linked to an increased risk to develop systemic lupus erythematosus (SLE) and other autoimmune diseases. Among these autoimmunity risk genes are IFN regulatory factor 5 (IRF5), which is involved in TLR signaling, and the signal transducer and activator of transcription 4 (STAT4) that interacts with the type I IFN receptor. Several other gene variants in the IFN signaling pathway also confer an increased risk to develop an autoimmune disease. The observations that IFN-α therapy can induce autoimmunity and that many autoimmune conditions have an on-going type I IFN production suggest that the type I IFN system has a pivotal role in the etiopathogenesis of these diseases. Possible mechanisms behind the dysregulated type IFNsystem in autoimmune diseases and how the IFN-α produced can contribute to the development of an autoimmune process will be reviewed.

Involvement of CD226+ NK cells in immunopathogenesis of systemic lupus erythematosus

Dysfunction of immune systems, including innate and adaptive immunity, is responsible for the immunopathogenesis of systemic lupus erythematosus (SLE). NK cells are a major part of the innate immune system, and diminished populations of NK cells have been reported in SLE patients. However, the mechanisms behind this decrease and the role of NK cells in SLE pathogenesis remain poorly understood. In this study, we found that a deficiency of NK cells, especially CD226(+) NK cells, is prominent in patients with active SLE. Meanwhile, expression of the CD226 ligands CD112 and CD155 on plasmacytoid dendritic cells is observed in SLE patients; thus, activation of CD226(+) NK cells may be induced by CD226-ligand interactions. Furthermore, IFN-α, which is mainly produced by plasmacytoid dendritic cells, can mediate the activation-induced cell death of NK cells. Therefore, these processes likely contribute to the loss of NK cells in patients with active SLE. Despite the impaired cytotoxicity of peripheral NK cells in human SLE patients and mouse SLE models, we provide evidence that CD226(+) NK cells infiltrate the kidneys of predisease MRL-lpr/lpr mice. Kidney-infiltrating NK cells displayed an activated phenotype and a marked ability to produce cytotoxic granules. These results suggest that, before apoptosis, activated NK cells can infiltrate tissues and, to some extent, mediate tissue injury by producing cytotoxic granules and immunoregulatory cytokines.

The type I interferon system in the development of lupus

The type I interferon (IFN) system induces inhibition of viral replication, but can also activate the innate and adaptive immune system. An important role of the type I IFN system in autoimmune diseases, including lupus, is suggested by the observation that these disorders display a prominent over-expression of type I IFN regulated genes. The development of autoimmune diseases in some individuals treated with IFN-α directly supports a pivotal role for this cytokine in breaking tolerance and inducing autoimmune reactions. A genetic setup that promotes type I IFN production and/or response and the presence of endogenous inducers of IFN-α production have been described in patients with lupus. Several known environmental risk factors for development of lupus or disease flares may contribute to the ongoing type I IFN production. In the present review we will describe the possible role of the type I IFN system in the lupus disease process. The possible connection between the type I IFN system and some environmental and genetic risk factors for lupus is also discussed.

High-mobility group box 1 (HMGB1) as a master regulator of innate immunity

Damage-associated molecular patterns (DAMPs) comprise intracellular molecules characterized by the ability to reach the extracellular environment, where they prompt inflammation and tissue repair. The high-mobility box group 1 (HMGB1) protein is a prototypic DAMP and is highly conserved in evolution. HMGB1 is released upon cell and tissue necrosis and is actively produced by immune cells. Evidence suggests that HMGB1 acts as a key molecule of innate immunity, downstream of persistent tissue injury, orchestrating inflammation, stem cell recruitment/activation, and eventual tissue remodeling.