Remnants of suicidal cells fostering systemic autoaggression. Apoptosis in the origin and maintenance of autoimmunity

Serum GAS6, sAXL, IL-10, NO, and BCL-2 levels are decreased in patients with Behçet's disease

PURPOSE

Behçet's disease (BD) is an autoimmune chronic systemic inflammatory disease characterized by a versatile clinical spectrum. Growth arrest specific protein 6 (GAS6)/soluble AXL (sAXL) signaling pathway draws attention in the resolution of inflammation, and its deficiency is associated with chronic inflammatory, autoimmune diseases, as well as clearance of apoptotic cells by phagocytes - efferocytosis. In this study, it was aimed to investigate whether GAS6/sAXL, interleukin (IL)-10, nitric oxide (NO), and BCL-2 levels were associated with inflammation and efferocytosis contributes to the pathogenesis of BD.

METHODS

A total of 37 Behçet patients with ocular involvement and 30 healthy control subjects were included in this study. GAS6, sAXL, IL-10, NO, and BCL-2 levels were quantified using enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

Serum GAS6, sAXL, IL-10, NO, and BCL-2 levels were significantly lower in patients with BD compared to the controls (P < 0.005, P < 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively). In correlation analysis, research parameters decreased in patients with BD was significantly correlated with each other: GAS6-IL-10 (r = 0.585, P < 0.001), GAS6-BCL-2 (r = 0.541, P < 0.001), sAXL-BCL-2 (r = 0.696, P < 0.001), IL-10-NO (r = 0.717, P < 0.001), IL-10-BCL-2 (r = 0.759, P < 0.001), and NO-BCL-2 (r = 0.541, P < 0.001).

CONCLUSION

In conclusion, decreased serum BCL-2 level may be an indicator of increased apoptosis in these patients and decreased levels of GAS6/sAXL, IL-10, and NO may indicate insufficient clearance of apoptotic bodies released as a result of increased apoptosis in BD patients.

Risk of rheumatoid arthritis diagnosis in statin users in a large nationwide US study

Objective

To evaluate the association between statin use and the risk of developing rheumatoid arthritis (RA) in a large, US case-control study.

Methods

Using the OptumLabs Data Warehouse, RA cases were identified as patients aged ≥18 years with ≥2 RA diagnoses between January 1, 2010 and June 30, 2019 and ≥1 prescription fills for methotrexate within 1 year of the first RA diagnosis. The first RA diagnosis was the index date. Cases were matched 1:1 to controls on age, sex, region, year of index date, and length of baseline coverage. Statin users were defined by having ≥2 statin prescription fills at least 90 days pre-index. Patients identified as statin users were further classified by statin user status (current or former), statin use duration, and intensity of statin exposure. Odds ratios for RA risk with statin use were estimated using logistic regression.

Results

16,363 RA cases and 16,363 matched controls were identified. Among RA cases, 5509 (33.7%) patients were statin users compared to 5164 (31.6%) of the controls. Statin users had a slightly increased risk of RA compared to non-users (OR 1.12, 95% CI 1.06–1.18), and former statin users had an increased RA risk compared to current users (OR 1.21, 95% CI 1.13–1.28). However, risk was eliminated following adjustment for hyperlipidemia. The risk estimates for statin use duration and intensity did not reach significance.

Conclusion

This study demonstrates no significant increase in the risk of developing RA for statin users compared to non-users after adjustment for hyperlipidemia in addition to other relevant confounders. However, more information from prospective studies would be necessary to further understand this relationship.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02617-5.

The Role of Efferocytosis in Autoimmune Diseases

Apoptosis happens continuously for millions of cells along with the active removal of apoptotic debris in order to maintain tissue homeostasis. In this respect, efferocytosis, i.e., the process of dead cell clearance, is orchestrated through cell exposure of a set of "find me," "eat me," and "tolerate me" signals facilitating the engulfment of dying cells through phagocytosis by macrophages and dendritic cells. The clearance of dead cells via phagocytes is of utmost importance to maintain the immune system tolerance to self-antigens. Accordingly, this biological activity prevents the release of autoantigens by dead cells, thus potentially suppressing the undesirable autoreactivity of immune cells and the appearance of inflammatory autoimmune disorders as systemic lupus erythematous and rheumatoid arthritis. In the present study, the apoptosis pathways and their immune regulation were reviewed. Moreover, efferocytosis process and its impairment in association with some autoimmune diseases were discussed.

Required role of apoptotic myogenic precursors and toll-like receptor stimulation for the establishment of autoimmune myositis in experimental murine models

OBJECTIVE

Muscle regeneration is a hallmark of the idiopathic inflammatory myopathies (IIMs), a group of autoimmune disorders that are characterized by leukocyte infiltration and dysfunction of the skeletal muscle. Despite detailed studies describing the clinical and histopathologic features of IIMs, the immunopathogenesis of these disorders remains undefined. The aim of this study was to investigate the immunopathologic processes of autoimmune myositis in experimental murine models.

METHODS

Expression of the autoantigen histidyl-transfer RNA synthetase (HisRS) was analyzed in mice with acutely injured or dystrophic muscles, in inflammatory leukocytes, and in purified satellite cells. Anti-HisRS antibodies and myositis induction were assessed in mice after muscle injury and immunization with apoptotic satellite cells or C2C12 myoblasts, in the presence or absence of the Toll-like receptor 7 (TLR-7) agonist R848.

RESULTS

Muscle necrosis, leukocyte infiltration, and myofiber regeneration induced by toxic agents (cardiotoxin or glycerol) or promoted by genetic disruption of the α-sarcoglycan/dystrophin complex in mice were uniformly associated with up-regulated expression of HisRS. Although regenerating myofibers and purified satellite cells are known to show increased expression of HisRS in these settings, anti-HisRS antibodies were not detectable. However, intramuscular immunization with ultraviolet B-irradiated, HisRS-expressing apoptotic myoblasts in the presence of R848 triggered the production of anti-HisRS IgG antibodies as well as persistent lymphocyte infiltration and prolonged/delayed muscle regeneration. Conversely, intramuscular administration of R848 alone or in combination with living or postapoptotic/necrotic myoblasts failed to generate this myositis phenotype.

CONCLUSION

In the presence of TLR/adjuvant signals and underlying muscle injury, apoptotic myogenic precursors expressing high levels of autoantigen can provoke autoantibody formation and lymphocytic infiltration of muscle tissue, effectively replicating the features of IIM.

Statins as a potential risk factor for autoimmune diseases: a case report and review

Association of statins with autoimmune disorders is rarely reported. We report a case of an apparently healthy 76-year-old woman who was on long-term statin therapy presenting with severe rhabdomyolysis, autoimmune hepatitis, and positive lupus antibodies. Patient presented with complaints of worsening fatigue, leg cramps, and progressive weakening of lower extremities over 3 weeks. The patient was on simvastatin daily for several years. Clinical examination on admission included muscle tenderness, lower extremity edema, and ascites. Her laboratory values on admission showed elevated creatine kinase and transaminases. Immunologic workup revealed positive ANA, anti-dsDNA and anti-SSA antibodies. F-actin antibody was also positive at high titer. Magnetic resonance imaging of the lower extremities showed findings consistent with myositis. Patient underwent biopsy of the thigh muscles, which showed inflammatory myositis. Liver biopsy was characteristic of autoimmune hepatitis. Patient responded well to immunosuppressive therapy with azathioprine and prednisone. Although statins are generally considered safe, recent data from long-term follow-up on patients who are on statins for long duration suggest that prolonged exposure to statins may trigger autoimmune reactions. The exact mechanism of statin-induced autoimmune reaction is unclear. Statins, as proapoptotic agents, release nuclear antigen into the circulation and may induce the production of pathogenic autoantibodies. The role of statins in inducing an endoplasmic reticular stress response with associated upregulation of major histocompatibility complex-1 expression and antigen presentation by muscle fibers has also been reported. Systemic immunosuppressive therapy has proven to be effective in many reported cases.

Instructive influences of phagocytic clearance of dying cells on neutrophil extracellular trap generation

Coordinated programmes of resolution are thought to initiate early after an inflammatory response begins, actively terminating leucocyte recruitment, allowing their demise via apoptosis and their clearance by phagocytosis. In this review we describe an event that could be implicated in the resolution of inflammation, i.e. the establishment of a refractory state in human neutrophils that had phagocytosed apoptotic cells. Adherent neutrophils challenged with apoptotic cells generate neutrophil extracellular traps (NETs), filaments of decondensed chromatin decorated with bioactive molecules that are involved in the capture of various microbes and in persistent sterile inflammation. In contrast, neutrophils that had previously phagocytosed apoptotic cells lose their capacity to up-regulate β2 integrins and to respond to activating stimuli that induce NET generation, such as interleukin (IL)-8. A defective regulation of NET generation might contribute to the persistent inflammation and tissue injury in diseases in which the clearance of apoptotic cells is jeopardized, including systemic lupus erythematosus and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis.

Endometriosis, a disease of the macrophage

Endometriosis, a common cause of pelvic pain and female infertility, depends on the growth of vascularized endometrial tissue at ectopic sites. Endometrial fragments reach the peritoneal cavity during the fertile years: local cues decide whether they yield endometriotic lesions. Macrophages are recruited at sites of hypoxia and tissue stress, where they clear cell debris and heme-iron and generate pro-life and pro-angiogenesis signals. Macrophages are abundant in endometriotic lesions, where are recruited and undergo alternative activation. In rodents macrophages are required for lesions to establish and to grow; bone marrow-derived Tie-2 expressing macrophages specifically contribute to lesions neovasculature, possibly because they concur to the recruitment of circulating endothelial progenitors, and sustain their survival and the integrity of the vessel wall. Macrophages sense cues (hypoxia, cell death, iron overload) in the lesions and react delivering signals to restore the local homeostasis: their action represents a necessary, non-redundant step in the natural history of the disease. Endometriosis may be due to a misperception of macrophages about ectopic endometrial tissue. They perceive it as a wound, they activate programs leading to ectopic cell survival and tissue vascularization. Clearing this misperception is a critical area for the development of novel medical treatments of endometriosis, an urgent and unmet medical need.

Phagocytosis of apoptotic cells by macrophages in anti-neutrophil cytoplasmic antibody-associated systemic vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of autoimmune diseases, including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). It is not known why ANCA develop, but it has been shown that they participate in pathogenesis by activating polymorphonuclear neutrophils (PMNs). In this study we hypothesize that dysregulation of phagocytosis in AAV leads to the accumulation of apoptotic neutrophils seen in association with blood vessels in AAV. These cells progress into secondary necrosis, contributing to tissue damage and autoantibody formation. Peripheral blood cells were counted, and phagocytosis was investigated using monocyte-derived macrophages (MØ) and PMNs from healthy blood donors (HBD), AAV patients and systemic lupus erythematosus (SLE) patients. Furthermore, the effect of serum was assessed. Phagocytosis was measured using flow cytometry. The results showed no deviation in monocyte subpopulations for AAV patients compared to HBDs, although there was a decrease in lymphocyte and pDC (plasmacytoid dendritic cell) populations (4·2 × 10(6) cells/l versus 10·4 × 10(6) cells/l, P < 0·001). The number of neutrophils was increased (6·0 × 10(9) cells/l versus 3·8 × 10(9) cells/l, P < 0·001). There were no differences found in the ability of MØs to engulf apoptotic cells, nor when comparing apoptotic PMNs to become engulfed. However, serum from AAV donors tended to decrease the phagocytosis ability of MØs (36%) compared to serum from HBDs (43%). In conclusion, there is no intrinsic dysfunction in the MØs or in the PMNs that have an effect on phagocytic activity, but ANCA may play a role by decreasing phagocytic ability.

Bovine lactoferrin improves bone status of ovariectomized mice via immune function modulation

We have previously shown that bovine lactoferrin (bLF) supplementation can have a beneficial effect on postmenopausal bone loss by modulating bone formation and resorption. A direct effect of bLF on bone metabolism is support by its presence in mice blood. Moreover we know that LF plays a key role in innate immunity and recent studies have shown its ability to modulate adaptive immunity. In particular bLF ingestion prevents recruitment and activation of immune cells at inflammatory sites. We propose that LF through its ability to modulate maturation and differentiation of leucocytes can participate to abolish the deregulation induced by estrogen deficiency on T cells. This study evaluated the effects of bovine lactoferrin on immune function in ovariectomized mice. We investigated whether bLF ingestion could prevent bone loss via modulation of immune function. Three-month-old female C3H mice were either ovariectomized or sham-operated and fed for 1, 2 or 4 months with a control diet (AIN-93M) or the same diet including 10g bLF/kg diet. Bone mineral density was determined using a Lunar Piximus densitometer. The immune parameters were assessed by flow cytometry. In addition, Real-Time PCR was performed to quantify TNFα expression and plasma cytokines were measured at 4 months with Luminex. Ovariectomy induced significant changes on bone parameters and increased recruitment of macrophages, dendritic cells, and B and T cells associated with T lymphocyte activation in bone marrow. Compared to the control diet, ingestion of bLF-enriched diet for 2 months prevented T cell activation and restored dendritic and B cell populations in the bone micro-environment in ovariectomized mice. Furthermore, TNFα expression in bone was decreased by bLF supplementation after 2 and 4 months. Similarly, a decreased plasma level of TNFα was observed concomitantly to an increase of IL-10 level. In conclusion, these experiments suggest that bLF can mediate the prevention of lymphocyte activation and cytokine release in the bone micro-environment. Dietary bLF supplementation could have a beneficial effect on postmenopausal bone loss by modulating immune function.

Epigenetic histone code and autoimmunity

The multiple inter-dependent post-translational modifications of histones represent fine regulators of chromatin dynamics. These covalent modifications, including phosphorylation, acetylation, ubiquitination, deimination, and methylation, affect therefore the numerous processes involving chromatin, such as replication, repair, transcription, genome stability, and cell death. Specific enzymes introducing modified residues in histones are precisely regulated, and a single amino acid residue can be subjected to a single or several, independent modifications. Disruption of histone post-translational modifications perturbs the pattern of gene expression, which may result in disease manifestations. It has become evident in recent years that apoptosis-modified histones exert a central role in the induction of autoimmunity, for example in systemic lupus erythematosus and rheumatoid arthritis. Certain histone post-translational modifications are linked to cell death (apoptotic and non-apoptotic cell death) and might be involved in lupus in the activation of normally tolerant lymphocyte subpopulations. In this review, we discuss how these modifications can affect the antigenicity and immunogenicity of histones with potential consequences in the pathogenesis of autoimmune diseases.

Proteomic analysis for the anti-apoptotic effects of cystamine on apoptosis-prone macrophage

Increased macrophage vulnerability is associated with progression of systemic lupus erythematosus. Our previous studies have shown that cystamine, an inhibitor of transglutaminase 2 (TG2), alleviated the apoptosis of hepatocyte and brain cell in lupus-prone mice NZB/W-F1. In present study, we further investigated the effects of cystamine on apoptosis-prone macrophages (APMs) in the lupus mice. Using two-dimensional gel electrophoresis (2-DE) analysis, we found that cystamine induced a differential protein expression pattern of APM as comparing to the PBS control. The protein spots presenting differential level between cystamine and PBS treatment were then identified by peptide-mass fingerprinting (PMF). After bioinformatic analysis, these identified proteins were found involved in mitochondrial apoptotic pathway, oxidative stress, and mitogen-activated protein (MAP) kinase-mediated pathway. Further investigation revealed that cystamine significantly decreased the levels of apoptotic Bax and Apaf-1 and the activity of caspase-3, and increased the levels of anti-apoptotic Bcl-2 in APM. We also found that these apoptotic mediators were up-regulated in a correlation with the progression of lupus severity in NZB/W-F1, which were little affected in BALB/c mice. We also found that the reduced serum glutathione was restored by cystamine in NZB/W-F1. Interestingly, the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in APM and the phagocytic ability was diminished in presence of cystamine. In conclusion, our findings indicate that cystamine significantly inhibited mitochondrial pathway, induced antioxidant proteins, and diminished phosphorylation of extracellular ERK1/2, which may alleviate the apoptosis and the phagocytic ability of APM.

The uptake by blood-borne phagocytes of monosodium urate is dependent on heat-labile serum factor(s) and divalent cations

Accumulation in tissues of post-apoptotic cells is a feature frequently observed in patients with systemic lupus erythematosus and in murine models of systemic autoimmune diseases. One of the endogenous danger molecules released by secondarily necrotic cells is monosodium urate (MSU), which is already established to be the causative agent of gout. Here, we show that MSU is taken up by eosinophils, neutrophils and monocytes in a process involving (a) heat-labile serum factor(s) and divalent cations. The uptake induces the release of the pro-inflammatory cytokines IL-1beta/IL-18/TNFalpha and IL-6/IL-8 by monocytes and PMN, respectively.

Apoptosis and Autoimmunity Induced by Clodronate in Systemic Lupus Erythematosus Mononuclear Circulating Cells

The aim of this study is to evaluate the effect of clodronate on apoptosis of human systemic lupus erythematosus circulating mononuclear cells and to analyze possible correlations with changes in autoantibody production in vitro. Lympho-monocytes from 20 SLE patients were isolated and incubated with or without addition of 1 μM clodronate for 72 hours. Apoptosis and release of genomic material was assessed by immunofluorescent detection of cleaved caspase-3 and by Cell-Death-Detection ELISAPLUS kit (Roche). Anti-Nucleosome IgG and anti-dsDNA IgM and IgG autoantibody levels were determined in supernatants by commercially available ELISA kits. Clodronate induced apoptosis in monocytes as confirmed by cleaved caspase-3 immunostaining and by quantification of cleaved nucleosome in the supernatants (treated 0.22±0.05 O.D. vs untreated 0.09±0.04 O.D.; P<0.001). This finding was coupled with a significant increasing in supernatants of IgG anti-Nucleosome (treated 6.5±1.1 vs untreated 5.5±0.6 IU/mL; p=0.001) and IgM (treated 3.0±1.3 vs 2.2±0.9 IU/mL; p=0.02) and IgG (treated 4.0±1.8 vs untreated 2.8±1.5 IU/mL; p=0.02) anti-dsDNA autoantibody levels. Our findings stressed the proapoptotic activity of clodronate, as well as its potential autoimmunity induction in SLE mononuclear circulating cells. Clinical studies could clarify the role of bisphosphonates on autoantibody production and worsening of disease activity.

Remnants of secondarily necrotic cells fuel inflammation in systemic lupus erythematosus

OBJECTIVE

Patients with systemic lupus erythematosus (SLE) are often characterized by cellular as well as humoral deficiencies in the recognition and phagocytosis of dead and dying cells. The aim of this study was to investigate whether the remnants of apoptotic cells are involved in the induction of inflammatory cytokines in blood-borne phagocytes.

METHODS

We used ex vivo phagocytosis assays comprising cellular and humoral components and phagocytosis assays with isolated granulocytes and monocytes to study the phagocytosis of secondarily necrotic cell-derived material (SNEC). Cytokines were measured by multiplex bead array technology.

RESULTS

We confirmed the impaired uptake of various particulate targets, including immunoglobulin-opsonized beads, by granulocytes and monocytes from patients with SLE compared with healthy control subjects. Surprisingly, blood-borne phagocytes from two-thirds of the patients with SLE took up SNEC, which was rarely phagocytosed by phagocytes from healthy control subjects or patients with rheumatoid arthritis. Supplementation of healthy donor blood with IgG fractions derived from patients with SLE transferred the capability to take up SNEC to the phagocytes of healthy donors. Phagocytosis-promoting immune globulins also induced secretion of huge amounts of cytokines by blood-borne phagocytes following uptake of SNEC.

CONCLUSION

Opsonization of SNEC by autoantibodies from patients with SLE fosters its uptake by blood-borne monocytes and granulocytes. Autoantibody-mediated phagocytosis of SNEC is accompanied by secretion of inflammatory cytokines, fueling the inflammation that contributes to the perpetuation of autoimmunity in SLE.

Anti‐nuclear autoantibodies: clinical utility for diagnosis, prognosis, monitoring, and planning of treatment strategy in systemic immunoinflammatory diseases

The determination of serum autoantibodies to nuclear and cytoplasmic cell components is relevant to the diagnosis of chronic immunoinflammatory disorders. Detection is based on screening methods that allow antibody binding to intact cell structures, followed by use of assays to demonstrate their antigen target specificity. The results can be used to help clinicians set diagnosis and estimate prognosis, plan further diagnostic work-up, monitoring strategy and sometimes therapeutic approach. To obtain such accuracy of use clinicians need to be involved in revealing the differential diagnostic potential of the autoimmune serology test programme by furnishing detailed clinical data on patients from whom serum samples have been obtained. Borders between positive and negative values should aim at attaining a high diagnostic specificity towards clinically important disease controls.

Multidimensional degradomics identifies systemic autoantigens and intracellular matrix proteins as novel gelatinase B/MMP-9 substrates

The action radius of matrix metalloproteinases or MMPs is not restricted to massive extracellular matrix (ECM) degradation, it extends to the proteolysis of numerous secreted and membrane-bound proteins. Although many instances exist in which cells disintegrate, often in conjunction with induction of MMPs, the intracellular MMP substrate repertoire or degradome remains relatively unexplored. We started an unbiased exploration of the proteolytic modification of intracellular proteins by MMPs, using gelatinase B/MMP-9 as a model enzyme. To this end, multidimensional degradomics technology was developed by the integration of broadly available biotechniques. In this way, 100-200 MMP-9 candidate substrates were isolated, of which 69 were identified. Integration of these results with the known biological functions of the substrates revealed many novel MMP-9 substrates from the intracellular matrix (ICM), such as actin, tubulin, gelsolin, moesin, ezrin, Arp2/3 complex subunits, filamin B and stathmin. About 2/3 of the identified candidates were autoantigens described in multiple autoimmune conditions and in cancer (e.g. annexin I, nucleolin, citrate synthase, HMGB1, alpha-enolase, histidyl-tRNA synthetase, HSP27, HSC70, HSP90, snRNP D3). These findings led to the insight that MMPs and other proteases may have novel (immuno)regulatory properties by the clearance of toxic and immunogenic burdens of abundant ICM proteins released after extensive necrosis. In line with the extracellular processing of organ-specific autoantigens, proteolysis might also assist in the generation of immunodominant 'neo-epitopes' from systemic autoantigens. The study of proteolysis of ICM molecules, autoantigens, alarmins and other crucial intracellular molecules may result in the discovery of novel roles for proteolytic modification.

The immune reaction against allogeneic necrotic cells is reduced in Annexin A5 knock out mice whose macrophages display an anti-inflammatory phenotype

Proteins of the annexin family bind to phospholipids in a Ca²⁺ dependent manner. The exposure of phosphatidylserine (PS) by apoptotic as well as necrotic cells is one major eat-me-signal for macrophages. Annexin A5 (Anx A5) preferentially binds to PS. The availability of Anx A5 knock out (KO) mice allowed us to investigate for the first time if endogenous Anx A5 modulates the immune response towards allogeneic cells. Furthermore, the effect of Anx A5 gene deletion on the phagocytic process as well as on the inflammatory reaction of macrophages was explored. We found that Anx A5 KO mice have a strongly reduced allogeneic cellular immune reaction against primary as well as secondary necrotic cells. In vivo phagocytosis experiments revealed that macrophages of Anx A5 KO mice displayed an increased uptake of necrotic cells. Additionally, an increased secretion of the anti-inflammatory cytokine IL-10 of isolated macrophages of Anx A5 KO mice after contact with necrotic cells was observed. Furthermore, the promoter activity of the Anx A5 gene was enhanced after stimulation of macrophages. The tumour size of an allogeneic tumour regressed faster when endogenous Anx A5 was present. These data demonstrate that endogenous Anx A5 influences the phagocytosis of necrotic cells, modulates the immune response towards allogeneic cells and acts as an inflammatory protein.

Dendritic cells and cytokines in human inflammatory and autoimmune diseases

Dendritic cells (DCs) produce cytokines and are susceptible to cytokine-mediated activation. Thus, interaction of resting immature DCs with TLR ligands, for example nucleic acids, or with microbes leads to a cascade of pro-inflammatory cytokines and skewing of T cell responses. Conversely, several cytokines are able to trigger DC activation (maturation) via autocrine, for example TNF and plasmacytoid DCs, and paracrine, for example type I IFN and myeloid DCs, pathways. By controlling DC activation, cytokines regulate immune homeostasis and the balance between tolerance and immunity. The increased production and/or bioavailability of cytokines and associated alterations in DC homeostasis have been implicated in various human inflammatory and autoimmune diseases. Targeting these cytokines with biological agents as already is the case with TNF and IL-1 represents a success of immunology and the coming years will expand the range of cytokines as therapeutic targets in autoinflammatory and autoimmune pathology.

The genetics and biology of Irf5-mediated signaling in lupus

Recently much attention was attracted to the importance of the type I interferon pathway in the initiation and development of the autoimmune disease systemic lupus erythematosus (SLE). Many SLE patients have increased serum levels of IFN-alpha and display an IFN gene expression "signature" characterized by strong overexpression of IFN-responsive genes in leukocytes and target tissues. Moreover, about 20% of cancer patients treated with IFN-alpha therapy manifest symptoms resembling SLE and some later develop the disease. One of the key genes of the IFN-alpha pathway, IRF5, was found to be strongly associated with SLE. Two functional SNPs lead to alternative splicing and altered steady-state level of IRF5 gene expression. Besides, the gene has a polymorphic inserion/deletion in exon 6, which contributes to the diversity in the isoform pattern of IRF5. Interestingly, recent studies have not found association of IRF5 with the other autoimmune diseases, such as rheumatoid arthritis or psoriasis, suggesting the unique role for IRF5 in the development of lupus. Here, we present the current knowledge on IRF5 genetics and its biological function and discuss the possible ways in which IRF5 contributes to susceptibility to SLE.

Secondary necrosis in multicellular animals: an outcome of apoptosis with pathogenic implications

In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane, followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation. In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be reviewed.

Lupus erythematosus and other autoimmune diseases related to statin therapy: a systematic review

BACKGROUND

Statins have been increasingly associated with drug-induced autoimmune reactions, including lupus erythematosus.

OBJECTIVE

To identify and determine the clinical and biological characteristics of statin-induced autoimmune reactions.

MATERIAL AND METHODS

The MEDLINE database (1966 to September 2005) was used to identify all reported cases of statin-induced autoimmune diseases. The keywords used were statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, adverse effects, autoimmune disease, lupus erythematosus, dermatomyositis and polymyositis.

RESULTS

Twenty-eight cases of statin-induced autoimmune diseases have been published so far. Systemic lupus erythematosus was reported in 10 cases, subacute cutaneous lupus erythematosus in three cases, dermatomyositis and polymyositis in 14 cases and lichen planus pemphigoides in one case. Autoimmune hepatitis was observed in two patients with systemic lupus erythematosus. The mean time of exposure before disease onset was 12.8+/-18 months; range 1 month-6 years. Systemic immunosuppressive therapy was required in the majority of cases. In many patients, antinuclear antibodies were still positive many months after clinical recovery. A lethal outcome has been recorded in two patients despite aggressive immunosuppressive therapy.

CONCLUSION

Long-term exposure to statins may be associated with drug-induced lupus erythematosus and other autoimmune disorders. Fatal cases have been reported despite early drug discontinuation and aggressive systemic immunosuppressive therapy.

Accelerated macrophage apoptosis induces autoantibody formation and organ damage in systemic lupus erythematosus

Increased monocyte/macrophage (Mphi) apoptosis occurs in patients with systemic lupus erythematosus (SLE) and is mediated, at least in part, by an autoreactive CD4(+) T cell subset. Furthermore, autoreactive murine CD4(+) T cells that kill syngeneic Mphi in vitro induce a lupus-like disease in vivo. However, it is unclear whether increased Mphi apoptosis in SLE per se is sufficient to accelerate/promote autoimmunity. We have investigated whether increased Mphi apoptosis in vivo, induced by the administration of clodronate liposomes, can exacerbate the autoimmune phenotype in NZB x SWR (SNF(1)) lupus-prone mice, and induce autoantibody production in haplotype-matched BALB/c x DBA1 (DBF(1)) non-lupus-prone mice. Lupus-prone mice SNF(1) mice that were treated with clodronate liposomes, but not mice treated with vehicle, developed significant increases in autoantibodies to dsDNA, nucleosomes, and the idiotypically related family of nephritic Abs Id(LN)F(1), when compared with untreated SNF(1) mice. Furthermore, clodronate treatment hastened the onset of proteinuria and worsened SNF(1) lupus nephritis. When compared with vehicle-treated controls, clodronate-treated non-lupus-prone DBF(1) mice developed significantly higher levels of anti-nucleosome and Id(LN)F(1) Abs but did not develop lupus nephritis. We propose that Mphi apoptosis contributes to the pathogenesis of autoantibody formation and organ damage through both an increase in the apoptotic load and impairment in the clearance of apoptotic material. This study suggests that mechanisms that induce scavenger cell apoptosis, such as death induced by autoreactive cytotoxic T cells observed in SLE, could play a pathogenic role and contribute to the severity of the disease.

Environmental adjuvants, apoptosis and the censorship over autoimmunity

Alterations during apoptosis lead to the activation of autoreactive T cells and the production of autoantibodies. This article discusses the pathogenic potential of cells dying in vivo, dissecting the role of signals that favor immune responses (adjuvants) and the influence of genetic backgrounds. Diverse factors determine whether apoptosis leads or not to a self-sustaining, clinically apparent autoimmune disease. The in vivo accumulation of uncleared dying cells per se is not sufficient to cause disease. However, dying cells are antigenic and their complementation with immune adjuvants causes lethal diseases in predisposed lupus-prone animals. At least some adjuvant signals directly target the function and the activation state of antigen presenting cells. Several laboratories are aggressively pursuing the molecular identification of endogenous adjuvants. Sodium monourate and the high mobility group B1 protein (HMGB1) are, among those identified so far, well known to rheumatologists. However, even the complementation of apoptotic cells with potent adjuvant signals fail to cause clinical autoimmunity in most strains: autoantibodies generated are transient, do not undergo to epitope/spreading and do not cause disease. Novel tools for drug development will derive from the molecular identification of the constraints that prevent autoimmunity in normal subjects.

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.

Prevalence of anticentromere F protein autoantibodies in 347 patients with non-Hodgkin's lymphoma

An association between autoimmunity and hematological malignancies has been reported including the detection of antinuclear autoantibodies (ANAs) in patients suffering from non-Hodgkin's lymphoma (NHL), with a high prevalence of ANAs directed to components of the mitotic apparatus or the mitosis-associated proteins. Previous studies have demonstrated that one of the targets of such ANAs could be the CENP-F protein, especially in some carcinomas. The prevalence and specificity of anti-CENP-F autoantibodies (aAbs) thus were analyzed in 347 patients with different histological subgroups of NHL before any treatment of NHL, along with 150 controls. The detection of these aAbs was performed using two techniques: a radioimmunological assay (RIA) and an indirect immunofluorescence technique (IIF). Twenty-five (7.2%) NHL patients and 2 (1.3%) control patients displayed anti-CENP-F aAbs using RIA. This difference between the two groups was found to be significant (P < 0.01), with a higher prevalence of aAbs in the follicular (13%) and in the marginal zone B and MALT (10.2%) lymphoma subgroups. By IIF, 10 (2.9%) patients with NHL displayed aAbs with a CENP-F or CENP-F-like pattern, whereas none of the control group did. In conclusion, these data demonstrate that a significant incidence of anti-CENP-F aAbs is observed, before any treatment, in some histological subgroups of NHL patients. In addition to the usefulness of anti-CENP-F aAbs as a marker for some NHL subgroups, prospective studies may be important to evaluate the predictive value of anti-CENP-F aAbs for the development of carcinomas.

Ultraviolet-B recruits mannose-binding lectin into skin from non-cutaneous sources

Mannose-binding lectin (MBL) is an integral part of the innate immune system and functions as an opsonin by binding to pathogens and certain apoptotic cells to promote their uptake by phagocytes. We recently identified an association of low-producing MBL polymorphisms with adult dermatomyositis (DM). Our model is that MBL deficiency leads to a defect in the clearance of apoptotic debris in the skin, thereby predisposing to photosensitive autoimmune disease. In this study, we sought to determine whether MBL binds within the epidermis, and to determine its source, and potential function of this binding. We demonstrated that the MBL is present in irradiated, but not in non-irradiated skin, and in irradiated skin it is bound to apoptotic keratinocytes (KC). We found that MBL is not made by KC, showing indirectly that it comes from an exogenous source, despite the fact that other complement components are made by KC and upregulated by ultraviolet irradiation. Finally, we demonstrated that non-KC-derived MBL bound to apoptotic KC in vitro and increased the uptake of these cells by dendritic cells. We hypothesize that MBL may facilitate non-inflammatory clearance of apoptotic debris in patients with photosensitive forms of DM.

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.

Influence on Spontaneous Tissue Inflammation by the Major Histocompatibility Complex Region in the Nonobese Diabetic Mouse

We investigated the role of the major histocompatibility complex (MHC) region in the specificity of autoimmunity by analysing specifically the development of sialadenitis, but also insulitis, nephritis and autoantibody production in autoimmune-prone nonobese diabetic (NOD) mice where the MHC H2g7 haplotype had been exchanged for the H2q (NOD.Q) or H2p (NOD.P) haplotype. The exchange of H2 haplotype did not affect the frequency of sialadenitis because the H2q and H2p congenic NOD strains developed sialadenitis with the same incidence as NOD. However, the severity of sialadenitis varied among the strains, as NOD.Q >NOD >NOD.P. At 11-13 weeks of age, the NOD.Q (H2q) female mice developed more severe sialadenitis compared to NOD.P (H2p) (P=0.038). At 20 weeks, the NOD (H2g7) female mice showed more severe sialadenitis than NOD.P (P=0.049). This is in contrast to the development of insulitis in the present strains, because the incidence of insulitis was almost completely inhibited by the replacement of the H2g7 haplotype of NOD. The incidence of insulitis in NOD.Q was 11-22%, compared to 75% in NOD, which correlated well with lower titres of anti-glutamic acid decarboxylase (anti-GAD) antibodies in NOD.Q compared to NOD (P=0.009). However, the introduction of the H2q haplotype into the NOD strain instead directed the autoimmune response towards the production of lupus types of autoantibodies, because the incidence of antinuclear antibodies (ANA) in NOD.Q was 89% compared with 11% in NOD.P and 12% in NOD mice, which in turn correlated with a high incidence of nephritis in NOD.Q compared to NOD. Consequently, we show that different haplotypes of MHC are instrumental in directing the specificity of the spontaneous autoimmune inflammation.

DNA as a marker of cell death in systemic lupus erythematosus

DNA circulates in the blood in systemic lupus erythematosus, among other conditions, and plays a role in immunopathogenesis in the form of immune complexes. As shown in experiments in mice, blood DNA levels rise following treatments to induce apoptosis and the administration of cells made apoptotic or necrotic in vitro. In mice lacking macrophage function, however, blood levels do not rise following administration of dead cells. These results indicate that circulating DNA may be a marker of cell death, although its levels likely reflect a complex process involving the interactions of macrophages with dead and dying cells.

Requirement of dying cells and environmental adjuvants for the induction of autoimmunity

OBJECTIVE

Cells commonly die without eliciting autoimmunity. However, dying cells are a potential initiating stimulus for systemic lupus erythematosus (SLE). Our goal was to verify whether immune adjuvants influence the autoimmunity induction that ensues following in vivo injection of dying cells.

METHODS

Mice were immunized with apoptotic thymocytes in the presence of artificial moieties, such as Freund's incomplete adjuvant (IFA), or natural adjuvants, such as dendritic cells (DCs). Renal involvement and the development of autoantibodies were monitored.

RESULTS

Apoptotic cells failed to induce clinical disease or to sustain production of autoantibodies in (NZB x NZW)F(1) mice. In contrast, autoimmunity developed in the presence of IFA or DCs. The characteristics of the adjuvant influenced the array of autoantibodies, the kinetics of their development, and the severity of the disease. DCs were required for induction of anti-beta(2)-glycoprotein I IgG. Adjuvants alone did not elicit disease.

CONCLUSION

A "two-hit" signal composed of autoantigens and adjuvants initiates systemic autoimmunity. Moreover, environmental signals at the site of clearance of dead cells shape the features and the severity of the autoimmune disease. Strategies aimed at preventing the accumulation of dying cells and at modulating endogenous adjuvants may be beneficial for the treatment of SLE.

The role of macrophages in the removal of apoptotic B-cells in the sheep ileal Peyer's patch

In the process of generating the cells that populate the sheep's B-cell pool, the ileal Peyer's patch (PP) produces an immense number of B-cells and then destroys most of them by apoptosis. Rapid clearance of these apoptotic cells is essential for tissue homeostasis and for preventing pathology. Macrophages comprise a small percentage of cells in the follicles. They resemble macrophages found in other tissues and can be identified by the expression of MHC Class II and CD14. In this study, enriched macrophages co-cultured with apoptotic ileal PP cells showed increased DNA content as they ingested apoptotic cells. The higher the proportion of apoptotic cells in culture the greater the increase in DNA content of the macrophages. This occurred when B-cell apoptosis was initiated by a period in culture or in response to treating the animals with steroids. Thus, macrophages resident in the ileal PP follicle mediate the phagocytosis and removal of discarded B-cells.

Lupus-Like Syndrome Associated with Statin Therapy

Statins are among the most widely prescribed drugs. An increasing number of lupus-like syndrome has recently been reported with these lipid-lowering agents. We describe a new case associated with simvastatin therapy. The presence of anti-dsDNA antibodies in the serum is for the first time reported confirming that statins may also induce a systemic autoimmune reaction. Statin-induced lupus-like syndrome is characterized by the long delay between the beginning of therapy and the skin eruption. Antinuclear antibodies may persist for many months after drug discontinuation. The causal relationship may be therefore difficult to establish, and probably many cases are unrecognized. Early diagnosis may avoid unnecessary immunosuppressive therapy.

Aberrant extracellular and dendritic cell (DC) surface expression of heat shock protein (hsp)70 in the rheumatoid joint: possible mechanisms of hsp/DC-mediated cross-priming

We describe, in rheumatoid arthritis (RA), abnormalities in the expression and distribution of heat shock protein (hsp) and dendritic cells (DCs) that are conducive to cross-priming and DC cross-talk. As detected by ELISA, inducible (i)hsp70 was dramatically increased in RA synovial fluid (RASF) vs normal human and RA sera and osteoarthritis and gout synovial fluid. Immunoblot analysis of fresh RASF cells revealed marked increases in ihsp70 and activation of its transcription factor heat shock factor-1, compared with fresh normal peripheral blood cells. Flow cytometry and microscopy demonstrated high levels of ihsp70 on the surface of RASF myeloid DCs (but not normal myeloid DCs) that occurred concurrently with hspRs (CD91/CD14). ihsp70 present in RASF exhibited chaperoning potential, as indicated by the capture of ihsp70 present in RASF on the surface of normal DCs. Binding was partially competitively inhibited by excess alpha(2)-macroglobulin, indicating that hspRs in addition to CD91 participate in the capture process. These data indicate that ihsp70 may chaperone autologous Ags into immature RASF DCs via hspRs, and that cross-talk between DCs coexpressing hsp/hspRs reflects a disease process in RA. The induction of surface ihsp70 on normal cells after sublethal heat stress and the release of ihsp70 from normal DCs after inflammatory stress also suggest that the pattern of ihsp70 expression in RASF occurs in response to sustained stress.

Accumulation of plasma nucleosomes upon treatment with anti-tumour necrosis factor-alpha antibodies

OBJECTIVE

Patients undergoing anti-tumour necrosis factor-alpha (TNF-alpha) treatment often develop autoantibodies. Apoptotic cell antigens are a potential initiating stimulus for autoantibodies. Our goal was to verify whether anti-cytokine therapy causes the release of nucleosomes, a major autoantigen generated during cell death.

DESIGN

Laboratory research study with comparison group.

SETTING

Clinical Immunology Unit and Lab, H San Raffaele University Hospital, Italy.

SUBJECTS

Eleven healthy controls and 87 rheumatic patients were studied, including 51 with rheumatoid arthritis (RA) and 33 patients with systemic lupus erythematosus (SLE).

INTERVENTIONS

Vein blood samples were taken via the antecubital vein. Blood was retrieved from 11 patients before and after injection of anti-TNF-alpha humanized antibodies. Nucleosomes were measured with an enzyme-linked immunosorbent assay. Cell death induced by anti-TNF-alpha antibodies and by the soluble cytokine was assessed in vitro.

MAIN OUTCOME MEASURES

Nucleosome level by treatment.

RESULTS

Enzyme-linked immunosorbent assay effectively detected nucleosomes either released by dying cells in vitro or circulating in the plasma. SLE but not RA patients had circulating nucleosomes at the steady state. Eight of 11 patients had significantly higher levels of plasma nucleosomes after infliximab. Minute amounts of TNF-alpha enabled infliximab to induce cell death in vitro.

CONCLUSIONS

The accumulation of nucleosomes possibly fosters the development of autoantibodies in subjects with appropriate genetic backgrounds.

Photosensitivity in rheumatic diseases

There have been a number of recent advances in the genetic understanding of photosensitive rheumatic diseases, especially subacute cutaneous lupus erythematosus and dermatomyositis. These advances support the concept that increased numbers of ultraviolet light-induced apoptotic cells in skin lead to a supra-threshold concentration of antigenic peptides. The current genetic data suggest that increased keratinocyte apopotosis can result from increased amounts of TNF-alpha that induce apoptosis due to a ultraviolet light-sensitive TNF promoter polymorphism or to decreased clearance of apototic cells due to polymorphisms associated with decreased serum levels of collectins such as C1q and mannose-binding lectin. These diseases are frequently oligogenic, and other yet to be elucidated genes will, in individual patients, lead to increased numbers of apoptotic cells associated with these cutaneous autoimmune diseases. In the presence of specific MHC class I and II genes, antigen-presenting cells initiate a primary immune response that leads to cutaneous, and likely systemic, autoimmune disease.

Identification of the B-cell epitopes of the early endosome antigen 1 (EEA1)

Early endosome antigen 1 (EEA1) is a target autoantigen in patients diagnosed with neurological and other autoimmune conditions. Eighteen of 65 sera (28%) that displayed a vesicular cytoplasmic staining pattern also immunoprecipitated the recombinant EEA1. These 18 sera were selected for further clinical, serological and epitope mapping studies. Thirty-six percent of the 18 patients had neurological diseases. Seventeen sera (94%) reacted with the partial length EEA1 constructs that included the C-terminal zinc finger (+FYVE) and the methyl accepting domain (LeuMA: amino acids 82-1411) in an addressable laser bead assay suggesting that the assay may be used for rapid laboratory detection of anti-EEA1 antibodies. Three of seven sera selected for epitope mapping studies bound to EEA1 peptides represented by amino acids 1096-1125, and two reacted with peptides represented by amino acids 1296-1320. One serum reacted only with the C-terminal peptide 1096-1125. The remaining serum reacted with other EEA1 epitopes. This data was supported by the observations that all the sera immunoprecipitated the C-terminal +FYVE (EEA1 1064-1411) construct, a peptide that also contained the linear epitopes 1096-1140. The limited epitope mapping studies suggest that the sera from patients with non-neurological diseases recognized epitopes in the central and C-terminal EEA1 domains, whereas the patients with neurological disease recognized a more restricted set of epitopes in the C-terminal.

Defective function of Fas in T cells from paediatric patients with autoimmune thyroid diseases

Triggering of the Fas receptor induces T cell apoptosis and is involved in shutting-off the immune response. Inherited defects impairing Fas function cause the autoimmune lymphoproliferative syndrome, and may play a role in other autoimmune diseases. The aim of this work was to analyse the Fas function in paediatric patients with thyroid autoimmunities. We found that T cells from 24/28 patients with Graves' disease (GD) and 12/35 patients with Hashimoto's thyroiditis (HT) displayed defective Fas function. In HT, the defect was more frequent in patients requiring replacement therapy (11/20) than in those not requiring (1/15); moreover, in untreated HT the highest defect was displayed by patients with the highest levels of autoantibodies. Fas was always expressed at normal levels and no Fas mutations were detected. Analysis of the healthy parents of seven Fas-resistant patients showed that several of them were Fas-resistant, which suggests a genetic component. Fusion of Fas-resistant T cells with the Fas-sensitive HUT78 T cell line generated Fas-resistant hybrid cells, which suggests the presence of molecules exerting a dominant negative effect on Fas function. Analysis of Fas-induced activation of caspase-8 and -9 showed decreased activity of both caspases in HT, whereas activity of caspase-9 was increased and that of caspase-8 was decreased in GD. These data suggest that heterogeneous inherited defects impairing Fas function favour the development of thyroid autoimmunities.

Caspase-mediated cleavage of the U snRNP-associated Sm-F protein during apoptosis

Recent studies have implicated the dying cell as a potential reservoir of modified autoantigens that might initiate and drive systemic autoimmunity in susceptible hosts. The spliceosomal Sm proteins are recognized by the so-called anti-Sm autoantibodies, an antibody population found exclusively in patients suffering from systemic lupus erythematosus. We have studied the effects of apoptosis on the Sm proteins and demonstrate that one of the Sm proteins, the Sm-F protein, is proteolytically cleaved in apoptotic cells. Cleavage of the Sm-F protein generates a 9-kDa apoptotic fragment, which remains associated with the U snRNP complexes in apoptotic cells. Sm-F cleavage is dependent on caspase activation and the cleavage site has been located near the C-terminus, EEED(81) downward arrow G. Use of different caspase inhibitors suggests that besides caspase-8 other caspases are implicated in Sm-F cleavage. A C-terminally truncated mutant of the Sm-F protein, representing the modified form of the protein, is capable of forming an Sm E-F-G complex in vitro that is recognized by many anti-Sm patient sera.

Induction of cell death by sera from patients with acute brain injury as a mechanism of production of autoantibodies

OBJECTIVE

To investigate the capacity of blood draining from the central nervous system of patients with acute brain injury to induce cell death, and to determine whether this phenomenon could be a way to induce the production of autoantibodies.

METHODS

The induction of cell death of several human leukemia cell lines cultured in vitro in the presence of serum collected from the brain or the systemic circulation of patients with acute brain injury was analyzed by flow cytometry after staining with annexin V and propidium iodide. The percentages of apoptotic lymphocytes derived directly from the patients were also quantified. To investigate the mechanisms responsible for the induction of cell death, the expression of apoptosis-related molecules, as well as the effect of addition of several molecules known to interfere with apoptosis, was evaluated in the cell cultures. The presence of serum autoantibodies at the time of injury and 6 months later was studied.

RESULTS

Systemic serum and, especially, serum draining from the brain lesions induced the in vitro death of the leukemia cell lines used. Moreover, there were higher percentages of ex vivo dead lymphocytes in regional blood than in systemic blood 48 hours after injury. These effects seemed to be induced by an exogenous and/or endogenous opioid, since they were blocked by the opioid antagonist, naloxone. Furthermore, such effects were mediated by an increased expression of Bax. Importantly, apoptotic Jurkat cells were bound to autoantibodies, and patients with acute brain injury produced serum autoantibodies some months after the injury. However, they did not develop a full autoimmune disease at that time.

CONCLUSION

Serum factors from acute brain injuries induce cell death, both in vivo and in vitro. Apoptotic cells and, even more so, necrotic cells in acute brain injury are potential sources for autoantigen presentation that may stimulate autoimmune responses.

Serum amyloid P component and C-reactive protein opsonize apoptotic cells for phagocytosis through Fcgamma receptors

Serum amyloid P component (SAP) and C-reactive protein (CRP) are opsonins that react with nuclear autoantigens targeted in systemic autoimmunity. CRP and SAP bind to apoptotic and necrotic cells, which are potential sources of these autoantigens. We have recently determined that the receptors for CRP on phagocytic cells are Fcgamma receptors. The goal of this study was to determine whether CRP and SAP promote phagocytosis of apoptotic cells and to identify the receptors involved. Apoptosis was induced in human neutrophils (PMN) and the Jurkat T-cell line by UV-irradiation. SAP treatment of apoptotic human PMN increased ingestion by autologous macrophages. Both SAP and CRP increased ingestion of apoptotic, but not normal Jurkat cells by J-774 macrophages and mouse peritoneal macrophages. Neither SAP nor CRP increased ingestion of apoptotic Jurkat cells by macrophages from FcR gamma-chain deficient mice, which lack FcgammaRI and FcgammaRIII. Inhibition of FcgammaRIII-mediated uptake using mAb 2.4G2 eliminated opsonization by SAP, but not by CRP. These results indicate that pentraxins promote uptake of apoptotic cells through FcgammaRI and/or FcgammaRIII. Ingestion through these receptors is expected to alter the pattern of cytokine production and antigen presentation in response to apoptotic cells.

Association of autoantibodies to nuclear lamin B1 with thromboprotection in systemic lupus erythematosus: lack of evidence for a direct role of lamin B1 in apoptotic blebs

OBJECTIVE

To demonstrate the association between autoantibodies to nuclear lamin B1 (aLB1) and protection against thrombosis ("thromboprotection") in patients with systemic lupus erythematosus (SLE), and to elucidate the mechanism by which aLB1 cause thromboprotection in vivo. Since a number of autoantigens in SLE have been localized specifically to the external surface of apoptotic blebs, it was hypothesized that circulating aLB1 may block the procoagulant effect of apoptotic blebs by binding to LB1 displayed at the external bleb surface.

METHODS

A cross-sectional study was performed using serum samples obtained at first evaluation of 259 English Canadian and French Canadian patients from SLE registries at 3 hospitals. A case-control study was performed to analyze the relationship between aLB1 and lupus anticoagulant (LAC) status and thrombotic manifestations between onset of disease and last followup. Reactivity of aLB1 with Jurkat or endothelial cells, which had been induced to undergo apoptosis, was determined by indirect immunofluorescence. Localization of LB1 in apoptotic cells and blebs was analyzed by confocal microscopy and surface labeling of cell membrane proteins.

RESULTS

High-titer aLB1 was restricted to a subset of SLE patients (46 patients), with an overall frequency of 17.8% (range 11.6-24.3% in the 3 centers). LB1 antibodies were significantly associated with LAC but not with antibodies to cardiolipin (aCL) or beta(2)-glycoprotein I (anti-beta(2)GPI). The frequency of thrombosis differed markedly depending on aLB1 and LAC status, as follows: presence of LAC and absence of aLB1 50%, presence of both LAC and aLB1 22.7%, absence of both LAC and aLB1 25.5%, absence of LAC and presence of aLB1, 20.8%. Further subclassification of patients based on aCL and anti-beta(2)GPI status revealed that, in the presence of LAC but in the absence of aCL, anti-beta(2)GPI, and aLB1, the frequency of thrombosis was 40%, whereas in the presence of aLB1, it decreased strikingly, to 9.1%. LB1 was found to be translocated into surface membrane blebs during apoptosis and to be entirely enclosed within the apoptotic bleb plasma membrane of Jurkat and endothelial cells.

CONCLUSION

The presence of aLB1 in SLE patients with LAC essentially nullifies the strong prothrombotic risk associated with LAC. Hence, aLB1 is associated with thromboprotection. Reactivity of aLB1 with apoptotic blebs does not seem to play a direct role in mediating this protection, since LB1 is buried within apoptotic blebs and inaccessible to circulating aLB1. The mechanism by which aLB1 confers thromboprotection in SLE remains to be elucidated.

Associations of tumor necrosis factor alpha and HLA polymorphisms with adult dermatomyositis: implications for a unique pathogenesis

We recently reported that the -308A tumor necrosis factor alpha promoter polymorphism is associated with the photosensitive disorder subacute cutaneous lupus erythematosus and mediates an exaggerated tumor necrosis factor alpha response to ultraviolet B. We now sought to examine the association of this polymorphism with adult dermatomyositis, a photosensitive disease that exhibits some features in common with subacute cutaneous lupus erythematosus. Fifty adult patients with dermatomyositis and 239 healthy, race-matched controls were examined for the -308A tumor necrosis factor alpha polymorphism and the more common -308G allele. The frequency of the -308A allele was 0.27 in the entire dermatomyositis group, versus 0.14 in the controls (p = 0.003, chi2 2 x 2 table). Caucasians were the only racial/ethnic group in our study large enough to allow separate statistical analysis (47 dermatomyositis, 223 controls). The frequency of the -308A allele was 0.26 for dermatomyositis and 0.14 for controls (p = 0.014). Caucasians are known to exhibit a linkage disequilibrium between -308A and HLA-DR3, which we previously found to be significantly enhanced in subacute cutaneous lupus erythematosus patients. In contrast, we now found no increase in the association of -308A and HLA-DR3 in Caucasians with dermatomyositis compared to controls. Consistent with this observation, the association of these two genes in dermatomyositis was significantly less than we previously reported in Caucasians with subacute cutaneous lupus erythematosus (p = 0.016). We conclude that the tumor necrosis factor -308A polymorphism is associated with dermatomyositis, which suggests a pathophysiologic contribution from ultraviolet-induced production of tumor necrosis factor alpha, similar to subacute cutaneous lupus erythematosus. The differences in linkage with HLA-DR3, as well as several divergent clinical features, indicate that there are also fundamental mechanistic differences between dermatomyositis and subacute cutaneous lupus erythematosus.

Caspase cleavage of the nuclear autoantigen LEDGF/p75 abrogates its pro-survival function: implications for autoimmunity in atopic disorders

Lens epithelium-derived growth factor p75 (LEDGF/p75) is a nuclear autoantigen in atopic disorders implicated in cellular protection against stress-induced apoptosis. We observed that LEDGF/p75 was cleaved during apoptosis into fragments of 65 and 58 kD generated by caspases-3 and -7 cleaving at three sites: DEVPD30/G, DAQD486/G and WEID85/N. Sequence analysis revealed that the DEVPD30/G and WEID85/N sites lie within the highly conserved HATH (homologous to amino terminus of hepatoma-derived growth factor) region, also known as PWWP domain. Alignment of proteins containing this domain failed to reveal conservation of the DEVPD30/G and WEID85/N sites, suggesting that the HATH/PWWP domain of LEDGF/p75 may be specifically targeted by caspases. Overexpression of LEDGF/p75 protected HepG2 cells from serum starvation-induced cell death, whereas expression of the 65 kD fragment failed to protect. The apoptotic cleavage of LEDGF/p75 may contribute to the pathogenesis of atopic disorders by abrogating its pro-survival function and enhancing its immunogenicity.

Phagocytosis of apoptotic cells by macrophages from NOD mice is reduced

Macrophages limit inflammatory responses by clearing apoptotic cells. Deficiencies in apoptotic cell phagocytosis have been linked to autoimmunity. In this study, we determined the efficiency with which macrophages from diabetes-prone NOD and diabetes-resistant NOR, Idd5, Balb/c, and C57BL/6 mice phagocytose apoptotic thymocytes and NIT-1 insulinoma cells. Peritoneal and bone marrow-derived macrophages from NOD mice engulfed fewer apoptotic thymocytes than macrophages from Balb/c mice (P < 0.05). Peritoneal macrophages from NOR and Idd5 NOD congenic mice were more proficient at engulfment than their NOD counterparts. Annexin V blockade diminished apoptotic thymocyte clearance and heat-labile serum factors augmented clearance. Binding of apoptotic thymocytes to NOD macrophages was also reduced, suggesting that the deficiency in phagocytosis may be partly attributable to a recognition defect. Peritoneal macrophages from female Balb/c and NOD mice were equally efficient in the engulfment of microspheres, suggesting that the phagocytic deficiency observed in NOD mice was specific for apoptotic cells. In summary, we have demonstrated a deficiency in phagocytic function of macrophages from NOD mice. Normal and diabetes-prone neonatal rodents have a wave of beta-cell apoptosis coincident with the onset of target organ inflammation. A constitutive defect in the clearance of apoptotic beta-cells may be contributory to the initiation of autoimmunity.