Etiopathogenesis of systemic lupus erythematosus

Interferon-alpha and viral triggers promote functional maturation of human monocyte-derived dendritic cells

BACKGROUND

Type I interferons (IFNs) play an important role in the pathogenesis of many autoimmune disorders including psoriasis. In the presence of IFN-alpha and granulocyte/macrophage colony-stimulating factor (GM-CSF), monocytes differentiate into dendritic cells (DCs) referred to as IFN-DCs. IFN-DCs potentially mimic DC populations involved in psoriasis and express a wide range of Toll-like receptor (TLR) subtypes.

OBJECTIVES

Recently, it was shown that single-stranded RNA (ssRNA) triggers TLR7 and TLR8; therefore we studied ssRNA, as a surrogate for ssRNA viruses and their impact on IFN-DCs.

METHODS

We established culture conditions for IFN-DCs, generated from plastic adherent monocytes using GM-CSF plus IFN-alpha. For DC stimulation ssRNA40, a 20-mer ssRNA oligonucleotide was used. The phenotypic analysis of DC preparations was performed using flow cytometry. The production of various cytokines was analysed by enzyme-linked immunosorbent assay, and real-time quantitative polymerase chain reaction was used to quantify TLR and cytokine gene expression. The ability of IFN-DCs to stimulate allogeneic T-cell proliferation was evaluated in a mixed leucocyte reaction.

RESULTS

We found that IFN-DCs express mRNA for TLR7 and TLR8 and that ssRNA stimulation significantly improves their costimulatory molecule expression, stabilizes their phenotype and enhances their capacity to stimulate naive T-cell proliferation. Unstimulated IFN-DCs did not produce bioactive interleukin (IL)-12 and produced low levels of other proinflammatory cytokines. In contrast, ssRNA stimulation led to a significant production of IL-12p70, IL-1beta, IL-6 and tumour necrosis factor alpha. IFN-DCs contained mRNA for IL-12p35, IL-12p40, IL-23p19, IL-27p28 and IL-27EBI, which was further increased by incubation with ssRNA.

CONCLUSIONS

Our study sheds light on a potential role for IFN-alpha and viral infections in triggering DC populations in psoriasis. These results provide additional data for the better understanding of human autoimmune and antiviral responses and may also have implications for strategies developing cancer immunotherapy.

Role of apoptosis failure in etiopathogenesis of systemic lupus erythematosus and murine lupus

Apoptosis serves many functions in the homeostasis of multicellular organisms. Defects in apoptosis may lead to clonal expansion and accumulation of autoreactive lymphocytes, which may result in the rare human autoimmune lymphoproliferative syndrome, a mild autoimmune reaction against cells in the blood. Defects in the clearance of apoptotic cells lead to accumulation of dying cells, which may enter later stages of cell death and release their contents, thereby critically contributing to the etiopathogenesis of the autoimmune disease systemic lupus erythematosus. For an efficient therapy of systemic lupus erythematosus, it is necessary to analyze apoptosis and clearance defects and to unravel factors leading to its onset.

Melatonin in relation to the "strong" and "weak" versions of the free radical theory of aging

That free radicals and the damage they inflict are related to deteriorative cellular and organismal changes associated with aging and also with the development of a variety of age-related diseases is widely debated. There seems to be little doubt that free radical mutilation of essential molecules contributes to these conditions. Numerous investigators, on the basis of their experimental results, have drawn this conclusion. If the free radical theory of aging and disease development has validity, antioxidants could presumably be successfully used to delay the molecular destruction, cellular loss, and organismal death. In the current review we summarize the experimental data related to the utility of melatonin in protecting against reactive oxygen and reactive nitrogen species-induced cellular damage. While the data supporting a role for melatonin in forestalling aging and prolonging life span per se is not compelling, the findings related to melatonin's ability to reduce the severity of a variety of age-related diseases that have as their basis free radical damage is convincing. To date, the bulk of these investigations have been performed in experimental models of diseases in animals. It is now imperative that similar studies be conducted using humans whose quality of life may benefit from treatment with melatonin.

Lymphadénite histiocytaire nécrosante ou maladie de Kikuchi-Fujimoto

Kikuchi-Fujimoto disease (KFD), first described independently by Kikuchi and Fujimoto in 1972, is a subacute necrotizing lymphadenitis of unknown cause. Although most frequent in young Asian women, KFD has a worldwide distribution. Clinically, KFD is characterized by lymphadenitis of one or more lymph nodes, predominantly in the posterior cervical region, fever, and leukopenia in up to 50% of cases. Extranodal manifestations can occur, especially skin lesions and aseptic meningitides. Diagnosis is usually confirmed by analysis of samples from an excisional biopsy of the affected nodes. Histologically, the lesions affect the cortical and paracortical areas of the node. Characteristic features include focal necrosis predominantly in the paracortical region with abundant karyorrhectic debris and atypical mononuclear cells around the necrotic zone (crescent-shaped histiocytes, plasmacytoid monocytes, and small lymphocytes and immunoblasts, mostly CD3(+)/CD8(+)), most often with an intact lymph node capsule, an absence of neutrophils, and a paucity of plasma cells. KFD has been classified into three histological subtypes and is thought to progress from the proliferative type (> 50%) to the necrotizing type (30%) and finally resolve into the xanthomatous type (< 20%). Differential diagnoses should include malignant lymphoma, infectious diseases such as toxoplasmatic lymphadenitis, tuberculous lymphadenitis and cat scratch disease, and systemic lupus erythematosus (SLE). The cause of KFD is unknown: a viral infection has been suggested, but not demonstrated, possibly involving human herpes virus 8 or Epstein-Barr virus. Apoptotic cell death plays a role: proliferating CD8(+) T-lymphocytes act as both killers and victims in the apoptotic process via Fas and perforin pathways. The course is usually benign with resolution in a few months with the use of antiinflammatory drugs. Regular follow-up is required because SLE may develop several years after the onset of Kikuchi-Fujimoto disease.

Dendritic cells and the immunopathogenesis of systemic lupus erythematosus

Over the last decade, the role of dendritic cells (DCs) in the immunopathogenesis of systemic lupus erythematosus (SLE) has become apparent. As unique mediators of both tolerance and immunity, aberrant myeloid and plasmacytoid DC function can promote autoimmune responses via a number of mechanisms and proinflammatory pathways. This review provides an overview of DC function, the potential role of DCs in promoting autoimmune responses in SLE, and how other abnormalities in lupus can lead to an enhanced engagement of DCs in immune responses. How medications used to treat SLE and other autoimmune conditions may exert effects on DCs is also explored.

Modulation of the immune system by dying cells and the phosphatidylserine-ligand annexin A5

Apoptotic cell death and the efficient clearance of dying cells are essential mechanisms to control tissue homeostasis and to eliminate potential autoantigens. Numerous alterations on the surfaces of dying cells define a highly characteristic membrane signature and enable an unequivocal distinction from vital cells. This way, phagocytosis is initiated and signalling events induced which minimize inflammatory reactions. Therefore, the use of proteins interfering with the clearance process may open up new vistas to improve immunization strategies and may help to understand the mechanisms of autoimmune diseases.

Removal of dying cells and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a very heterogeneous systemic autoimmune disease, in which autoantibody synthesis against nuclear constituents is the main immunological characteristic. These autoantibodies underwent affinity maturation and isotype switching. Additionally, T-cell tolerance against nuclear autoantigens should be affected in these autoimmune patients. Nuclear material derived from apoptotic and/or necrotic cells may serve as an important source of autoantigens. However, dead and dying cells as well as cellular debris are rapidly removed from tissues by phagocytes without eliciting inflammation or immune responses under healthy conditions. During apoptosis nuclear components are strongly modified through enzymatic reactions. If these cells are not timely cleared, those autoantigens may be released, taken up, and presented by dendritic cells in tissues or presented by follicular dendritic cells in lymph nodes to T and B cells, respectively. This could be a mechanism for breaking the peripheral self-tolerance. In this article we focus on the deficient clearance of apoptotic cells in SLE patients and its importance in development of this autoimmune disease.

Identification of type I interferon-associated inflammation in the pathogenesis of cutaneous lupus erythematosus opens up options for novel therapeutic approaches

Cutaneous lupus erythematosus (CLE) is one of the most common dermatological autoimmune disorders worldwide. Recently, several studies provided evidence for a pathogenic role of type I interferons (IFNs) in this disease. Plasmacytoid dendritic cells are major type I IFN producers in CLE skin lesions. Type I IFNs are able to induce the expression of several proinflammatory chemokines, including CXCL9 and 10, and enhance the cytotoxic capacity of infiltrating cells. Additionally, adhesion molecules and chemokine receptors, such as intercellular adhesion molecule-1, cutaneous lymphocyte antigen, E-selectin, CCR4 and CXCR3, are involved in the recruitment of potentially autoreactive lymphocytes into the skin. Here, we review the role of type I IFNs, adhesion molecules and chemokine receptors in CLE and discuss options for novel therapeutic approaches.

Physiopathologie du lupus érythémateux systémique

Innate immunity is directly implicated in the pathophysiology of lupus through the dendritic cell system and the activation by immune complexes of some toll-like receptors (TLR). Interferon-alpha plays a key role in the pathophysiology of lupus and represents a promising target for immune therapy. Dendritic cells are activated and able to capture large quantities of nuclear antigen-containing bodies to stimulate specific adaptive immune response.

Accumulation of apoptotic cells in the epidermis of patients with cutaneous lupus erythematosus after ultraviolet irradiation

OBJECTIVE

To examine whether apoptosis contributes to the pathogenesis of skin lesions in patients with cutaneous lupus erythematosus (CLE) after ultraviolet (UV) irradiation.

METHODS

In situ nick translation and TUNEL were performed to detect apoptosis in 85 skin biopsy specimens from patients with various subtypes of CLE. Specimens from normal healthy donors and patients with polymorphous light eruption were used as controls. In addition to assessment of primary lesions, provocative phototesting was carried out to investigate events occurring secondary to UV irradiation during a very early stage of lesion formation.

RESULTS

A significant increase in apoptotic nuclei was found in the upper epidermal layer of primary and UV light-induced skin lesions of CLE patients compared with controls. In tissue sections obtained from control subjects at 24 hours after a single exposure to UV light, a slight increase in the count of epidermal apoptotic nuclei was present as compared with skin tissue from CLE patients obtained under the same conditions before lesion formation. In sections obtained from controls at 72 hours after irradiation, a significant decrease in the apoptotic nuclei count was observed, consistent with a proper clearance of apoptotic cells in the period between 24 and 72 hours after irradiation. In striking contrast, the number of apoptotic nuclei increased significantly within this period in tissue sections from patients with CLE.

CONCLUSION

These data support the hypothesis that apoptotic cells accumulate in the skin of patients with CLE after UV irradiation, as a result of impaired or delayed clearance. The nonengulfed cells may undergo secondary necrosis and release proinflammatory compounds and potential autoantigens, which may contribute to the inflammatory micromilieu that leads to formation of skin lesions in this disease.

Involvement of phosphatidylserine, alphavbeta3, CD14, CD36, and complement C1q in the phagocytosis of primary necrotic lymphocytes by macrophages

OBJECTIVE

Uningested dead cells may be an important source of autoantigens and may trigger autoimmune diseases such as systemic lupus erythematosus (SLE). Multiple receptors involved in the clearance of apoptotic cells have been described; however, little is known about the receptors and ligands involved in uptake of necrotic cells that release autoantigens as well.

METHODS

The uptake of autologous necrotic peripheral blood lymphocytes into human monocyte-derived macrophages was qualitatively and quantitatively monitored by confocal microscopy and 2-color flow cytometry, respectively. Blocking experiments were performed to examine the receptors and molecules involved in the phagocytosis of necrotic cells. Cytokine secretion by lipopolysaccharide-activated monocytes and macrophages was determined by enzyme-linked immunosorbent assay.

RESULTS

Phosphatidylserine, which was exposed on necrotic as well as apoptotic cells, promoted the recognition and removal of primary necrotic lymphocytes. Several macrophage receptor systems, including the thrombospondin-CD36-alphavbeta3 complex, CD14, and the complement component C1q, contributed to the engulfment of necrotic cells. Necrotic peripheral blood lymphocytes slightly increased the lipopolysaccharide-induced secretion of interleukin-10 and reduced the secretion of tumor necrosis factor alpha in monocytes and macrophages.

CONCLUSION

Our results indicate that at least some of the receptors and adaptors mediating the uptake of apoptotic cells are also involved in the clearance of necrotic cells. Hence, necrotic cells engage phagocyte receptors such as CD36, which mediate antiinflammatory signals from apoptotic cells. Necrotic cells consequently also have the potency to provide antiinflammatory signals to phagocytes; however, these signals may be overridden by proinflammatory factors released during necrosis. These findings have implications regarding the etiopathogenesis of autoimmune diseases such as SLE, in which impaired clearance of dead cells may foster autoimmunity by the release of potential autoantigens.

[An impaired detection and clearance of dying cells can lead to the development of chronic autoimmunity]

Not properly cleared dead cells are dangerous for the body. The dead cells accumulate, lose their membrane integrity, danger signals are released, and nuclear antigens get accessible in an inflammatory context. In times of increased apoptosis, tolerance can be broken, a chronic inflammation results which then can lead to an autoimmune reaction against nuclear constituents. An impaired clearance of dying cells represents a central pathogenic process in the development of chronic autoimmune diseases like in systemic lupus erythematosus (SLE). Many adaptor molecules and receptors are involved in the clearance of dying cells. Complement components, serum DNase I, phosphatidylserine, and modified glycoproteins participate crucially in the clearance of apoptotic and necrotic cells. We further observed intrinsic defects of macrophages of some SLE patients. Macrophages as well as granulocytes of some SLE patients showed heterogeneous clearance defects. Furthermore, we observed an accumulation of nuclear material in germinal centres of lymph nodes of some SLE patients. The non-ingested nuclear material may provide survival signals for autoreactive B cells and consecutively antinuclear autoantibodies (ANA) will be produced. We therefore conclude that drugs promoting the phagocytosis are important candidates of specific therapies in the future which expect a more gentle and purposive treatment of patients with SLE.

Photosensitivity in lupus erythematosus

Lupus erythematosus (LE) is an autoimmune disease which can be triggered by environmental factors such as solar irradiation. It has long been observed that especially ultraviolet (UV) exposure can induce and exacerbate skin lesions in patients with this disease. However, despite the frequency of photosensitivity in LE, the mechanisms by which UV irradiation activates autoimmune responses is only now becoming increasingly unfolded by advanced molecular and cellular biological investigations. Phototesting, according to a standardized protocol with UVA and UVB irradiation has proven to be a valid model to study photosensitivity in various subtypes of LE and to evaluate the underlying pathomechanisms of this disease. Detailed analysis of the molecular events that govern lesion formation in experimentally photoprovoced LE showed increased accumulation of apoptotic keratinocytes and impaired expression of the inducible nitric oxide synthase (iNOS). In the near future, gene expression profiling and proteomics will further increase our knowledge on the complexity of the "UV response" in LE. This review summarizes the current understanding of the clinical and molecular mechanisms that initiate photosensitivity in this disease.

Reduced uptake of apoptotic cells by macrophages in systemic lupus erythematosus: correlates with decreased serum levels of complement

BACKGROUND

Defects in phagocytosis of apoptotic cells have a role in the pathogenesis of autoimmune diseases. Decrease of phagocytosis of apoptotic cells occurs in systemic lupus erythematosus (SLE). Factors underlying this decrease are, presently, unknown.

OBJECTIVE

To analyse the expression of relevant membrane receptors of monocyte derived macrophages (MDM) from patients with SLE and assess their ability to phagocytose apoptotic cells in comparison with MDM from healthy controls. Additionally, to compare phagocytosis in the presence of SLE sera with that in normal human serum (NHS).

METHODS

Human peripheral blood monocytes were isolated from patients and controls, and cultured for 7 days to obtain MDM. Membrane expression of CD14, CD18, CD36, and CD51/61 was measured. MDM were incubated with apoptotic Jurkat cells in the presence of NHS or serum from patients with active or inactive disease.

RESULTS

No differences in phagocytosis capacity were found between MDM from patients and controls. Membrane expression of the respective receptors was comparable in patients and controls. However, when MDM from controls were incubated with apoptotic cells in patient serum, phagocytosis was significantly decreased in comparison with incubation in NHS. This effect depended on the patients' disease activity and could be reversed by addition of NHS. Reduced uptake of apoptotic cells was associated with decreased levels of complement C1q, C4, and C3, but not with levels of complement factor B.

CONCLUSIONS

Reduced uptake of apoptotic cells by MDM from patients with SLE is not an intrinsic defect but is serum dependent and associated with decreased levels of C1q, C4, and C3.

The pattern recognition receptor PTX3 is recruited at the synapse between dying and dendritic cells, and edits the cross-presentation of self, viral, and tumor antigens

Pentraxins are soluble pattern recognition receptors with a dual role: protection against extracellular microbes and autoimmunity. The mechanisms by which they accomplish these tasks are not yet fully understood. Here we show that the prototypic long pentraxin PTX3 is specifically recruited at both sides of the phagocytic synapse between dendritic cells (DCs) and dying cells and remains stably bound to the apoptotic membranes (estimated half-time > 36 hours). Apoptotic cells per se influence the production of PTX3 by maturing DCs. When both microbial stimuli and dying cells are present, PTX3 behaves as a flexible adaptor of DC function, regulating the maturation program and the secretion of soluble factors. Moreover a key event associated with autoimmunity (ie, the cross-presentation of epitopes expressed by apoptotic cells to T cells) abates in the presence of PTX3, as evaluated using self, viral, and tumor-associated model antigens (vinculin, NS3, and MelanA/MART1). In contrast, PTX3 did not influence the presentation of exogenous soluble antigens, an event required for immunity against extracellular pathogens. These data suggest that PTX3 acts as a third-party agent between microbial stimuli and dying cells, contributing to limit tissue damage under inflammatory conditions and the activation of autoreactive T cells.

[Pathogenic links between Kikuchi's disease and lupus: a report of three new cases]

INTRODUCTION

Histiocytic necrotizing lymphadenitis or Kikuchi-Fujimoto's disease is a rare anatomoclinical entity whose etiology remains unknown. It is mainly reported in young adult female, presenting with cervical lymphadenopathies, fever and asthenia. The diagnosis is based on the histological examination of a lymph node biopsy. The disease course is usually uneventful, but sometimes Kikuchi-Fujimoto's disease can reveal or evolve into a cutaneous or a systemic lupus.

EXEGESIS

We report three new cases of Kikuchi's disease: the first one mimicked a systemic lupus, the second one was associated with a lupus-like rash, and a the last one was a severe case with hemophagocytic syndrome and a primo-infection with Epstein-Barr virus revealing a systemic lupus erythematosus.

CONCLUSION

Clinical and biological follow-up of patients presenting with Kikuchi's disease is necessary to look for an association with a lupus. We discuss the pathogenic links between Kikuchi's disease and lupus.

Levels of complement in sera from inactive SLE patients, although decreased, do not influence in vitro uptake of apoptotic cells

BACKGROUND

Accumulation of apoptotic cells is considered relevant in the pathogenesis of systemic lupus erythematosus (SLE). Complement factors facilitate the clearance of apoptotic cells and, when decreased, might result in an increased amount of apoptotic cells found in SLE patients.

OBJECTIVE

To determine the influence of complement profiles from inactive SLE patients on the in vitro phagocytosis of apoptotic cells.

METHODS

Consecutive SLE patients (n=98) with inactive disease (SLEDAI < or =4) and 20 healthy controls (HC) were included. Levels of CH50, C3, C4, C1q, and C1r were measured. Human peripheral blood monocytes were isolated from healthy controls and cultured for 7 days to obtain monocyte-derived macrophages (MDM). Jurkat cells were irradiated with UVB to induce apoptosis. Phagocytosis was tested by incubation of MDM with apoptotic cells in the presence of serum and quantified as phagocytosis index (number of Jurkat cells internalized by 100 macrophages). Serum from 20 patients with CH50<65%, 20 patients with CH50 > or =65%, and 20 HC were used in this assay.

RESULTS

All HC and 37% of patients had normal complement levels. CH50 level was decreased in 21% of patients, C3 in 52%, C4 in 29%, C1q in 2% and C1r in 44% of patients. Between patients and HC, differences in level of CH50, C3 and C4 were statistically significant. No difference in phagocytosis index between HC and patients, irrespective of their CH50 level, was detected. No correlation was found between the respective complement levels and phagocytosis index.

CONCLUSION

In most SLE patients with inactive disease, levels of one or more complement components are decreased. However, decreased levels of complement do not result in a significantly reduced in vitro uptake of apoptotic Jurkat cells by MDM.

SLE—a disease of clearance deficiency?

Systemic lupus erythematosus (SLE) is a multifactorial disease and its pathogenesis and precise aetiology remain unknown. Under physiological conditions, neither apoptotic nor necrotic cell material is easily found in tissues because of its quick removal by a highly efficient scavenger system. Autoantigens are found in apoptotic and necrotic material and they are recognized by autoimmune sera from SLE patients. The clearance of dying cells is finely regulated by a highly redundant system of receptors on phagocytic cells and bridging molecules, which detect molecules specific for dying cells. Changes on apoptotic and necrotic cell surfaces are extremely important for their recognition and further disposal. Some SLE patients seem to have an impaired ability to clear such apoptotic material from tissues, and this could cause the breakdown of central and peripheral mechanisms of tolerance against self-antigens. In this article, we address the cells, receptors and molecules involved in the clearance process and show how deficiencies in this process may contribute to the aetiopathogenesis of SLE.

Impaired clearance of dying cells in systemic lupus erythematosus

Impaired clearance of apoptotic cell material has been implicated in the pathogenesis of systemic lupus erythematosus (SLE). Besides many other molecules, C1q and DNaseI contribute to an efficient clearance of dying cells. A frequently observed factor in SLE patients is the accumulation of unusually large amounts of apoptotic cells in various tissues. We showed that in a subgroup of patients with SLE, apoptotic cells accumulated in the germinal centers of the lymph nodes. The numbers of tingible body macrophages usually containing engulfed apoptotic nuclei were significantly reduced in these patients. Furthermore, we differentiated macrophages from CD34+ stem cells of SLE patients and NHD in vitro to analyze whether the observed clearance defects are intrinsic. Indeed, macrophages from SLE patients showed a reduced phagocytic capability. Very interestingly, those macrophages from different SLE patients, as well as granulocytes from these patients, showed in part different phagocytic defects, suggesting a heterogeneous clearance defect. We conclude that a failure of clearance in the early phase of apoptosis leads to a secondary necrotic status of the cells. Danger signals are released, modified autoantigens are accessible, and an autoimmune reaction gets started.

Defects in the disposal of dying cells lead to autoimmunity

The fast and efficient uptake of dying cells is of main importance to prevent contact of the immune system with intracellular autoantigens. Insufficient clearance of the latter is discussed to drive the humoral autoimmune response in systemic lupus erythematosus. Many adaptor molecules and receptors are involved in the recognition of dying cells. In this paper we focus on the involvement of phosphatidylserine, glycoproteins, and complement and DNaseI in the clearance of apoptotic and necrotic cells, respectively. Furthermore, extracellular danger signals released from necrotic cells are discussed and the uptake process of primary necrotic cells is investigated in detail. Last but not least, the character and origin of clearance defects observed in some systemic lupus erythematosus patients is presented.

Treatment of murine lupus using nucleosomal T cell epitopes identified by bone marrow-derived dendritic cells

OBJECTIVE

Systemic lupus erythematosus (SLE) is characterized by the existence of a heterogeneous group of autoantibodies directed against intact nuclear structures, such as nucleosomes. The most prominent of these autoantibodies are those directed against double-stranded DNA (dsDNA) and histones. The majority are of the IgG isotype and show affinity maturation, both of which are known hallmarks of T cell help. Much evidence suggests that the nucleosome is a major candidate autoantigen in SLE. In this study, a novel strategy was used to identify the critical CD4+ T cell autoepitopes in nucleosomes. In addition, peptide-based therapy was then performed in a lupus animal model.

METHODS

Bone marrow (BM)-derived dendritic cells (DCs) were used to examine the self-T cell responses against nucleosomes and to characterize the T cell epitope(s) of nucleosomes in (NZB x NZW)F1 (BWF1) mice.

RESULTS

Several potential auto-T cell epitopes of core histone proteins (H2A, H2B, H3, and H4) were identified. Nucleosome-pulsed BM-derived DCs elicited release of interleukin-4 and interferon-gamma, representing a Th0 (i.e., mixed Th1 and Th2) pattern of cytokine production. In addition, intradermal immunization of BWF1 mice with the H3(111-130) peptide not only suppressed the level of anti-dsDNA and anti-single-stranded DNA IgG, but also significantly delayed the progress of glomerulonephritis in lupus-prone BWF1 mice.

CONCLUSION

These results will help in understanding how pathogenic autoimmune responses develop in spontaneous SLE. This may potentially open the way to T cell-based immunotherapy for lupus.

Apoptosis and systemic lupus erythematosus

Reduced clearance of dying cells by macrophages or increased apoptosis provokes accumulation of cellular fragments in various tissues. This process seems to induce the uptake of autoantigens from apoptotic nuclei or chromatin by dendritic cells (DCs). Then, the DCs present altered self-epitopes to naive T cells. Thus, autoreactive T cells are activated accidentally and may now provide T-cell help for B cells that present peptides processed from secondary necrotic/late apoptotic prey. Impaired phagocytic removal of early apoptotic cells may cause accumulation of secondary necrotic cells and debris in the germinal centers of secondary lymph organs. The latter bind complement and can, therefore, be trapped on the surfaces of follicular DCs (FDCs). B cells may get in contact with intracellular autoantigens that had been released during late stages of apoptotic cell death and are immobilized by FDCs. Consecutively, B cells that had, for example, gained specificity for nuclear auto-antigens during random somatic mutations can receive a short-term survival signal. After migration into the mantle zone, these autoreactive B cells may finally be activated by autoreactive CD4+ T helper cells. B cells then differentiate into memory or plasma cells. The plasma cells produce those pathogenic nuclear autoantibodies. Many defects are known with respect to the clearance of apoptotic cells and cell material, especially that of nuclear origin. Reflecting on the plethora of defects of clearance of apoptotic material already demonstrated in systemic lupus erythematosus, it is reasonable to argue that, for many patients, failure of clearance is at the heart of their disease.

Endothelial cell apoptosis in systemic lupus erythematosus: a common pathway for abnormal vascular function and thrombosis propensity

Women with systemic lupus erythematosus (SLE) are at risk for premature atherothrombosis independent of Framingham risk factors. We investigated whether endothelial cell (EC) apoptosis predicts abnormal vasomotor tone and contributes to circulating tissue factor (TF) levels in this disease. Brachial artery flow-mediated dilation (FMD) and nitroglycerin-mediated dilation were determined in women with SLE, healthy control subjects, and subjects with coronary artery disease (CAD) (n = 43/group). Quantification of circulating apoptotic ECs was performed by flow cytometry (CD146+ cells that stained for Annexin V [CD146AnnV+]) and immunofluorescent microscopy. Plasma TF was measured by enzyme-linked immunosorbent assay (ELISA). Compared with healthy control and CAD subjects, patients with SLE had higher numbers of circulating CD146AnnV+ cells (10 ± 3, 18 ± 5, and 89 ± 32 cells/mL, respectively, mean ± SEM; P &lt; .01). Increased CD146AnnV+ cells correlated strongly with abnormal vascular function (P = .037). After adjusting for known predictors of endothelial function, CD146AnnV+ was the only variable that predicted FMD (β = –4.5, P &lt; .001). Increased CD146AnnV+ was strongly associated with elevated levels of circulating TF (r = .46, P = .002). Circulating apoptotic ECs are elevated in young women with SLE and strongly correlate with markedly abnormal vascular function and elevated TF levels. Heightened endothelial apoptosis may represent an important mechanism for development of atherothrombosis in SLE.

Flow cytometric evaluation of a model for phagocytosis of cells undergoing apoptosis

Phagocyte recognition of cells undergoing apoptosis is a rapid, efficient way of removing unwanted cells from tissue. The uptake of apoptotic cells prevents the release of potentially toxic cell contents that might otherwise damage neighbouring cells and elicit an inflammatory response. The aim of this work was to evaluate a simple cell culture assay to study phagocytosis of cells undergoing apoptosis. Fluorescent negatively charged beads (1 microm) or fluorescently labelled apoptotic cells, derived from etoposide-treated human monocytes (U937), were co-incubated with J774 cells or human peripheral blood macrophages for 1 h. Flow cytometry (FCM) showed an efficient uptake of both beads and apoptotic bodies. Phagocytosis of apoptotic cells but not of beads was significantly inhibited when macrophages were pre-incubated with cytochalasin D, suggesting that an experimental system based on beads is not an appropriate model of phagocytosis of apoptotic cells.

Cooperation between C1q and DNase I in the clearance of necrotic cell-derived chromatin

OBJECTIVE

The efficient uptake of dying cells by phagocytes is essential to the avoidance of chronic inflammation. Some human autoimmune responses are thought to be driven by autoantigens from apoptotic or necrotic cells. We analyzed the role of C1q and DNase I in the disposal of necrotic cell-derived chromatin because deficiencies in these serum factors predispose to the development of systemic autoimmune disorders, such as systemic lupus erythematosus.

METHODS

Human necrotic peripheral blood lymphocytes were incubated in cell culture medium supplemented with various sera or serum components. Chromatin degradation was monitored by measuring the residual DNA content by flow cytometry. The uptake of necrotic cell-derived nuclei was analyzed by in vitro phagocytosis assays.

RESULTS

Reconstitution of C1q-depleted serum with C1q strongly increased its ability to degrade necrotic cell-derived chromatin. Although C1q itself displayed no DNase activity, it strongly augmented the activity of serum DNase I. Whereas an excess of recombinant DNase I degraded chromatin in the absence of C1q, efficient uptake of the predigested material by monocyte-derived phagocytes required the presence of C1q. These data show that C1q and DNase I cooperate in the degradation of chromatin from necrotic cells. Furthermore, C1q was found to be necessary for effective uptake of degraded chromatin by monocyte-derived phagocytes.

CONCLUSION

C1q or DNase I deficiencies may precipitate autoimmunity in humans by a mechanism similar to that of other molecules that are involved in the safe, efficient, and rapid disposal of dying cells.

Exposure of anionic phospholipids serves as anti-inflammatory and immunosuppressive signal--implications for antiphospholipid syndrome and systemic lupus erythematosus

In contrast to necrotic cells, the clearance of apoptotic ones usually is an anti-inflammatory process which elicits only a marginal immune response. During apoptosis phosphatidylserine (PS) is exposed on the outer leaflet of the cytoplasmic membrane and serves as target for the PS receptor of phagocytes. The latter is responsible for anti-inflammatory signalling and the induction of TGFbeta. We were interested whether the immunogenicity of apoptotic cells can be increased by masking PS. We observed that treatment of xenogeneic apoptotic cells with annexin V (AxV) significantly increased the humoral immune response against surface epitopes of these cells. Furthermore, AxV-coated irradiated tumour cells were able to elicit a long lasting tumour specific cytotoxic T lymphocyte response. AxV efficiently blocked the uptake of irradiated cells by macrophages but not by dendritic cells. Furthermore, AxV skewed the phagocytosis of irradiated cells towards inflammation. Investigation of patients with autoimmune diseases further supported the role of anionic surface phospholipids for anti-inflammatory clearance of apoptotic cells. Impaired clearance and opsonisation with anti-phospholipid-antibodies are discussed to be responsible for the development of systemic lupus erythematosus and anti-phospholipid-syndrome, respectively. Presentation of cryptic epitopes from late apoptotic cells in a proinflammatory context may challenge T cell tolerance. In addition, accumulation of uncleared apoptotic debris in the germinal centres of lymph nodes may result in the survival of autoreactive B cells.

Interferon and granulopoiesis signatures in systemic lupus erythematosus blood

Systemic lupus erythematosus (SLE) is a prototype systemic autoimmune disease characterized by flares of high morbidity. Using oligonucleotide microarrays, we now show that active SLE can be distinguished by a remarkably homogeneous gene expression pattern with overexpression of granulopoiesis-related and interferon (IFN)-induced genes. Using the most stringent statistical analysis (Bonferroni correction), 15 genes were found highly up-regulated in SLE patients, 14 of which are targets of IFN and one, defensin DEFA-3, a major product of immature granulocytes. A more liberal correction (Benjamini and Hochberg correction) yielded 18 additional genes, 12 of which are IFN-regulated and 4 granulocyte-specific. Indeed immature neutrophils were identified in a large fraction of SLE patients white blood cells. High dose glucocorticoids, a standard treatment of disease flares, shuts down the interferon signature, further supporting the role of this cytokine in SLE. The expression of 10 genes correlated with disease activity according to the SLEDAI. The most striking correlation (P < 0.001, r = 0.55) was found with the formyl peptide receptor-like 1 protein that mediates chemotactic activities of defensins. Therefore, while the IFN signature confirms the central role of this cytokine in SLE, microarray analysis of blood cells reveals that immature granulocytes may be involved in SLE pathogenesis.

Systemic lupus erythematosus and the type I interferon system

Patients with systemic lupus erythematosus (SLE) have ongoing interferon-alpha (IFN-alpha) production and serum IFN-alpha levels are correlated with both disease activity and severity. Recent studies of patients with SLE have demonstrated the presence of endogenous IFN-alpha inducers in such individuals, consisting of small immune complexes (ICs) containing IgG and DNA. These ICs act specifically on natural IFN-alpha-producing cells (NIPCs), often termed plasmacytoid dendritic cells (PDCs). Given the fact that the NIPC/PDC has a key role in both the innate and adaptive immune response, as well as the many immunoregulatory effects of IFN-alpha, these observations might be important for the understanding of the etiopathogenesis of SLE. In this review we briefly describe the biology of the type I IFN system, with emphasis on inducers, producing cells (especially NIPCs/PDCs), IFN-alpha actions and target immune cells that might be relevant in SLE. On the basis of this information and results from studies in SLE patients, we propose a hypothesis that explains how NIPCs/PDCs become activated and have a pivotal etiopathogenic role in SLE. This hypothesis also indicates new therapeutic targets in this autoimmune disease.

The natural interferon-alpha producing cells in systemic lupus erythematosus

Prolonged exposure of the immune system to type I interferons (IFN-alpha/beta/omega) in patients receiving IFN-alpha therapy frequently results in development of autoantibodies and autoimmune disease. This is attributed to the many immunostimulatory effects of these cytokines. Patients with the autoimmune disease systemic lupus erythematosus (SLE) have an ongoing IFN-alpha production. Recent studies of SLE demonstrated the presence of endogenous IFN-alpha inducers, acting specifically on natural IFN-alpha producing cells (NIPC), often termed plasmacytoid dendritic cells (PDC). These IFN-alpha inducers were potent, present at the blood level, and characterized as immune complexes that contained DNA and IgG as essential components. They were considered a likely reason for the activated IFN-alpha production in SLE, which, in turn, might be an important etiopathogenic factor. Here, we briefly review the biology of the type I IFN system, with emphasis on inducers, producing cells (especially NIPC/PDC), IFN-alpha actions, and target immune cells, which might be relevant in SLE. Based on such information and results from studies in SLE patients, we propose a hypothesis that explains how NIPC/PDC become activated and play a pivotal etiopathogenic role in SLE and perhaps also other autoimmune diseases. This hypothesis furthermore indicates new therapeutic targets.

The apoptotic ligands TRAIL, TWEAK, and Fas ligand mediate monocyte death induced by autologous lupus T cells

Individuals with systemic lupus erythematosus show evidence of a significant increase in monocyte apoptosis. This process is mediated, at least in part, by an autoreactive T cell subset that kills autologous monocytes in the absence of nominal Ag. We have investigated the apoptotic pathways involved in this T cell-mediated process. Expression of the apoptotic ligands TRAIL, TNF-like weak inducer of apoptosis (TWEAK), and Fas ligand on lupus T cells was determined, and the role of these molecules in the monocyte apoptotic response was examined. We report that these apoptotic ligands mediate the autologous monocyte death induced by lupus T cells and that this cytotoxicity is associated with increased expression of these molecules on activated T cells, rather than with an increased susceptibility of lupus monocytes to apoptosis induced by these ligands. These results define novel mechanisms that contribute to increased monocyte apoptosis characterizing patients with lupus. We propose that this mechanism could provide a source of potentially antigenic material for the autoimmune response and interfere with normal clearing mechanisms.

Apoptosis of the teratocarcinoma cell line Tera-1 leads to the cleavage of HERV-K10gag proteins by caspases and/or granzyme B

Redistribution, post-translational modifications and coclustering with viral antigens contribute to the immunogenicity of apoptotic cell-derived autoantigens. Almost all known targets of the humoral autoimmune response in systemic lupus erythematosus (SLE) are cleaved by caspases or granzyme B during apoptosis. Antibodies against retroviral proteins can frequently be detected in the sera of SLE patients without overt retroviral infections. These antibodies may represent cross-reactive antibodies or may have been induced by proteins encoded by endogenous retroviral sequences. We used Tera-1 cells that abundantly express a group-specific antigen of human endogenous retroviruses, HERV-K10gag polyprotein, to investigate its processing during apoptosis. Tera-1 cells induced to undergo apoptosis showed an altered HERV-K10gag processing compared with viable cells. In addition, granzyme B was able to cleave HERV-K10gag isolated from viable Tera-1 cells. Similar to nuclear autoantigens, endogenous retroviral proteins are cleaved during the execution phase of apoptosis. These post-translational modifications may result in the generation of T-cell neoepitopes or a changed epitope hierarchy of retroviral proteins. Therefore, immunogenicity of retroviral antigens in SLE patients may result from a similar mechanism as described for nuclear autoantigens.

In vivo tolerance breakdown with dendritic cells pulsed with U1A protein in non-autoimmune mice: the induction of a high level of autoantibodies but not renal pathological changes

One of the hallmarks of systemic autoimmune diseases, such as systemic lupus erythematosus (SLE), is the immune response to nuclear autoantigens. Several studies have proposed that dendritic cells may acquire the nuclear autoantigens from the apoptotic cells to initiate the systemic autoimmune responses. To examine the immune response to a nuclear autoantigen induced by dendritic cells, bone marrow-derived dendritic cells (BMDCs) pulsed with U1 small nuclear ribonucleoprotein (snRNP)-A protein (U1A) were intravenously injected into non-autoimmune mice. The results showed that BMDCs pulsed with U1A proteins by intravenous injection into BALB/c (H-2d) and DBA-2xNZW F1 (H-2d/u) mice were capable of activating the autoreactive T cells and inducing a high titre of immunoglobulin G (IgG) anti-U1A antibodies. Both groups of mice with a high anti-U1A autoantibody titre also transiently developed IgG against double-stranded (ds) DNA. However, unlike NZBxNZW F1 (BWF1) (H-2d/u) mice, no obviously histopathological changes to the glomeruli were noted in the mice treated either with BMDCs or with U1A-pulsed BMDCs. Several months after immunization, all mice treated with U1A-pulsed BMDCs did develop IgG, but not the complement C3 deposit in the glomeruli. The cytokine profile produced by the U1A-specific T cells of primed DBA-2xNZW F1 mice was skewed toward the T helper type 1 phenotype compared with that of BWF1 mice. The model we describe here adds to the further understanding of the pathogenic mechanisms, such as self-antigen shifting, and the mechanisms that account for the different responses to self-antigens when in a normal or an autoimmune state.

Lupus-specific kidney deposits of HSP90 are associated with altered IgG idiotypic interactions of anti-HSP90 autoantibodies

Previous studies have shown that autoantibodies to heat shock protein 90 (HSP90) are elevated in a significant proportion of patients with systemic lupus erythematosus (SLE) who are more likely to have renal disease and a low C3 level. Using samples from 24 patients, we searched for glomerular deposits of HSP90 in renal biopsy specimens from seven patients with lupus nephritis and 17 cases of glomerulonephritis from patients without SLE. Positive glomerular immunofluorescent staining for HSP90 was observed in six of seven cases of SLE and positive tubular staining in two of seven SLE patients. The staining for HSP90 was granular in nature and was located in subepithelial, subendothelial and mesangial areas. None of the non-SLE renal biopsies revealed positive staining for HSP90 deposition. Further we showed the presence of anti-HSP90 IgG autoantibodies in IgG from sera of patients with SLE as well as in normal human IgG (IVIg). In normal IgG this autoreactivity could be adsorbed almost completely on F(ab')2 fragments from the same IgG preparation, coupled to Sepharose and could be inhibited by the effluent obtained after subjecting normal IgG to HSP90 affinity column. These findings indicate that anti-HSP90 natural autoantibodies are blocked by idiotypic interactions within the IgG repertoire. Unlike natural autoantibodies, anti-HSP90 IgG from SLE patients' sera were only moderately adsorbed on F(ab')2 fragments of normal IgG. These results demonstrate that immunopathogenesis of lupus nephritis is associated with HSP90 (as an autoantigen) and that the pathology is associated with altered idiotypic regulation of the anti-HSP90 IgG autoantibodies.

Oxidative stress inhibits the phagocytosis of apoptotic cells that have externalized phosphatidylserine

The efficient phagocytosis of apoptotic cells by macrophages reduces the potential for an inflammatory response by ensuring that the dying cells are cleared before their intracellular contents are released. Early apoptotic cells are targeted for phagocytosis through the translocation of phosphatidylserine (PS) from the inner to the outer leaflet of the plasma membrane. In this report, we show that the oxidant H(2)O(2) inhibits phagocytosis of apoptotic cells even though the cells express functional PS on their surface. Thus, B lymphoma cells induced to undergo apoptosis by the chemotherapy drug etoposide are efficiently phagocytosed by macrophages in a process that is mediated by PS (inhibitable by PS liposomes). Exposure of the apoptotic cells to H(2)O(2) inhibits phagocytosis even though the cells still express functional PS on their surface. In addition, Jurkat cells and thymocytes induced to undergo apoptosis by H(2)O(2) alone are poorly phagocytosed. Inhibition of phagocytosis by H(2)O(2) cannot be attributed to oxidative inactivation or redistribution of PS on the cell surface. The results indicate that PS externalization is necessary but is not sufficient to target apoptotic cells for phagocytosis. Another phagocytosis recognition factor must therefore exist to facilitate uptake of apoptotic cells, and this factor is sensitive to modification by H(2)O(2).

Direct transfer of p65 into T lymphocytes from systemic lupus erythematosus patients leads to increased levels of interleukin-2 promoter activity

The recent identification of a number of molecular defects in T cells from patients with systemic lupus erythematosus (SLE) has raised expectations for gene replacement therapy as an option in the treatment of these diseases. In this report, we have adapted an electroporation-based technique to transfer successfully DNA to peripheral blood T cells from normal individuals and patients with systemic lupus erythematosus and rheumatoid arthritis. Transfection efficiency, judged by the percentage of live cells expressing green fluorescence after transfection with a pGFP (green fluorescence protein), reached 32 +/- 3% in normal, 13 +/- 3% in SLE, and 17 +/- 13% in RA T cells. The transfection efficiency was slightly higher in CD8+ than in CD4+ cells, and the cells maintained acceptable (75%) viability up to the fourth post-transfection day. SLE T cells have been shown to display low levels of the p65 subunit of the NF-kappaB transcription factor and decreased production of IL-2. Since NF-kappaB contributes to the transcriptional regulation of the IL-2 promoter, the effect of the forced replenishment of p65 on IL-2 transcription was tested. The low level of interleukin-2 promoter activity in SLE T cells increased to normal levels following transfection with cDNA encoding the NF-kappaB p65 subunit. Taken together, these results demonstrate the feasibility of transfection of T cells from SLE patients by electroporation and the reversal of decreased interleukin-2 promoter activity in SLE T cells, and are an early step toward gene therapy as a method of treatment for these individuals.

Naturally processed chromatin peptides reveal a major autoepitope that primes pathogenic T and B cells of lupus

Major autoepitopes for pathogenic Th cells of lupus were previously found in core histones of nucleosomes by testing overlapping synthetic peptides. To detect other dominant epitopes, we eluted peptides from MHC class II molecules of a murine lupus APC line that was fed with crude chromatin. The eluted peptides were purified by reverse-phase HPLC and tested for their ability to stimulate autoimmune Th clones, and then analyzed by mass spectrometry. Amino acid sequences of stimulatory fractions revealed three new autoepitopes. Two of the epitopes were homologous to brain transcription factor BRN-3, whereas the third sequence was homologous to histone H1'(22-42). H1'(22-42) stimulated autoimmune Th cells to augment the production of pathogenic antinuclear Abs, and was much more potent than other nucleosomal epitopes in accelerating glomerulonephritis in lupus-prone (SWR x NZB)F(1) (SNF(1)) mice. Remarkably, a marked expansion of Th1 cells recognizing the H1'(22-42) epitope occurred spontaneously in SNF(1) mice very early in life. A significant proportion of H1'(22-42)-specific T cell clones cross-reacted with one or more core histone epitopes, but not with epitopes in other lupus autoantigens. The H1'(22-42) epitope was also recognized by autoimmune B cells, and with the onset of lupus nephritis, serum autoantibodies to the H1'(22-42) epitope become increasingly cross-reactive with nuclear autoantigens. Convergence of T and B cell epitopes in H1'(22-42) and its ability to elicit a cross-reactive response make it a highly dominant epitope that could be targeted for therapy and for tracking autoimmune T and B cells.

Alterations in molecular killing mechanisms: implications in skin disease

Cytolytic T lymphocytes exert two main specific molecular killing mechanisms against target cells, namely (i) they can synthesize and release soluble cytolytic factors, and (ii) they can express effector molecules that act as ligands of receptors expressed by target cells on the cell surface; by these two pathways cytolytic T lymphocytes kill several targets, e.g. cells infected with intracellular pathogens, cells transformed by malignancy and cells producing autoantibodies. This review investigates the contribution from alterations in these molecular killing mechanisms to the pathogenesis of cutaneous diseases. In fact, molecular components involved in such killing mechanisms are often altered or distorted in skin pathology, e.g. cutaneous viral infections, skin cancer, contact hypersensitivity and autoimmune diseases with cutaneous involvement. Treatments capable of repairing the molecular components operating in such killing mechanisms could presumably favour the resolution of these skin diseases.

Induction of dendritic cell differentiation by IFN-alpha in systemic lupus erythematosus

Dendritic cells (DCs) are important in regulating both immunity and tolerance. Hence, we hypothesized that systemic lupus erythematosus (SLE), an autoimmune disease characterized by autoreactive B and T cells, may be caused by alterations in the functions of DCs. Consistent with this, monocytes from SLE patients' blood were found to function as antigen-presenting cells, in vitro. Furthermore, serum from SLE patients induced normal monocytes to differentiate into DCs. These DCs could capture antigens from dying cells and present them to CD4-positive T cells. The capacity of SLE patients' serum to induce DC differentiation correlated with disease activity and depended on the actions of interferon-alpha (IFN-alpha). Thus, unabated induction of DCs by IFN-alpha may drive the autoimmune response in SLE.

An etiopathogenic role for the type I IFN system in SLE

The type I interferon (IFN) system plays a pivotal role in the etiopathogenesis of systemic lupus erythematosus (SLE). The initial appearance of autoantibody-producing B cells can be precipitated by infection-induced type I IFNs, but the further, significant generation of autoimmune T and B cells is caused by the prolonged production of IFN-alpha, which is maintained by a vicious circle mechanism. This involves the activation of immature dendritic cells, known as natural IFN-producing cells, by continuously formed endogenous IFN-alpha inducers. These IFN-alpha inducers consist of complexes of autoantibodies with nucleic-acid-containing autoantigens derived from apoptotic cells.

Mutation of DNASE1 in people with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly prevalent human autoimmune diseases that causes progressive glomerulonephritis, arthritis and an erythematoid rash. Mice deficient in deoxyribonuclease I (Dnase1) develop an SLE-like syndrome. Here we describe two patients with a heterozygous nonsense mutation in exon 2 of DNASE1, decreased DNASE1 activity and an extremely high immunoglobulin G titer against nucleosomal antigens. These data are consistent with the hypothesis that a direct connection exists between low activity of DNASE1 and progression of human SLE.