Therapy targeting antigen-specific T cells by a peptide-based tolerizing vaccine against autoimmune arthritis.

A longstanding goal has been to find an antigen-specific preventive therapy, i.e., a vaccine, for autoimmune diseases. It has been difficult to find safe ways to steer the targeting of natural regulatory antigen. Here, we show that the administration of exogenous mouse major histocompatibility complex class II protein bounding a unique galactosylated collagen type II (COL2) peptide (Aq-galCOL2) directly interacts with the antigen-specific TCR through a positively charged tag. This leads to expanding a VISTA-positive nonconventional regulatory T cells, resulting in a potent dominant suppressive effect and protection against arthritis in mice. The therapeutic effect is dominant and tissue specific as the suppression can be transferred with regulatory T cells, which downregulate various autoimmune arthritis models including antibody-induced arthritis. Thus, the tolerogenic approach described here may be a promising dominant antigen-specific therapy for rheumatoid arthritis, and in principle, for autoimmune diseases in general.

Two major genes associated with autoimmune arthritis, Ncf1 and Fcgr2b, additively protect mice by strengthening T cell tolerance.

A breach of T cell tolerance is considered as a major step in the pathogenesis of rheumatoid arthritis. In collagen-induced arthritis (CIA) model, immunization with type II collagen (COL2) leads to arthritis in mice through T cells responding to the immunodominant COL2259-273 peptide. T cells could escape from thymus negative selection because endogenous COL2259-273 peptide only weakly binds to the major histocompatibility complex class II (MHCII) molecule Aq. To investigate the regulation of T cell tolerance, we used a new mouse strain BQ.Col2266E with homozygous D266E mutations in the Col2 gene leading to a replacement of the endogenous aspartic acid (D) to glutamic acid (E) at position 266 of the COL2259-273 peptide, resulting in stronger binding to Aq. We also established BQ.Col2264R mice carrying an additional K264R mutation changed the lysine (K) at position 264 to eliminate the major TCR recognition site. The BQ.Col2266E mice were fully resistant to CIA, while the BQ.Col2264R mice developed severe arthritis. Furthermore, we studied two of the most important non-MHCII genes associated with CIA, i.e., Ncf1 and Fcgr2b. Deficiency of either gene induced arthritis in BQ.Col2266E mice, and the downstream effects differ as Ncf1 deficiency reduced Tregs and was likely to decrease expression of autoimmune regulator (AIRE) while Fcgr2b did not. In conclusion, the new human-mimicking mouse model has strong T cell tolerance to COL2, which can be broken by deficiency of Fcgr2b or Ncf1, allowing activation of autoreactive T cells and development of arthritis.

Toll-like receptor 2 is required for autoantibody production and development of renal disease in pristane-induced lupus.

OBJECTIVE: The mechanisms involved in breaking immunologic tolerance against nuclear autoantigens in systemic lupus erythematosus (SLE) are not fully understood. Our recent studies in nonautoimmune mice provided evidence of an important role of Toll-like receptor 2 (TLR-2) in antichromatin autoantibody induction by high mobility group box chromosomal protein 1-nucleosome complexes derived from apoptotic cells. The objective of this study was to investigate whether TLR-2 signaling is required for the induction of autoantibodies and the development of SLE-like disease in murine pristane-induced lupus. METHODS: Lupus-like disease in C57BL/6 and TLR-2(-/-) mice was induced by pristane injection. The numbers of immune cells and serum cytokine concentrations were determined by flow cytometry. Renal disease was assessed by quantification of proteinuria, histologic analyses, and enzyme-linked immunospot assay. RESULTS: Pristane-injected TLR-2(-/-) mice generated reduced numbers of splenic CD138+/cytoplasmic κL/λL chain-positive plasma cells and displayed diminished IgG responses against double-stranded DNA, histones, nucleosomes, some extractable nuclear autoantigens, and cardiolipin when compared with wild- type controls. TLR-2 deficiency prevented the pristane-induced systemic release of interleukin-6 (IL-6) and IL-10. The absence of TLR-2 attenuated peritoneal recruitment of CD11c+ cells and formation of lipogranulomas. Importantly, the renal disease that developed in pristane-treated TLR-2(-/-) mice was less severe than that in control mice, as reflected by milder proteinuria, reduced glomerular deposition of IgG and complement, and decreased renal infiltration of autoantibody-secreting cells. CONCLUSION: TLR-2 is required for the production of prototypical lupus autoantibodies and the development of renal disease in pristane-induced murine lupus. Interference with TLR-2 signaling may be a promising novel strategy for the treatment of SLE.

NCF4 regulates antigen presentation of cysteine peptides by intracellular oxidative response and restricts activation of autoreactive and arthritogenic T cells.

Autoimmune diseases, such as rheumatoid arthritis (RA) and systemic lupus erythematous, are regulated by polymorphisms in genes contributing to the NOX2 complex. Mutations in both Ncf1 and Ncf4 affect development of arthritis in experimental models of RA, but the different regulatory pathways mediated by NOX2-derived reactive oxygen species (ROS) have not yet been clarified. Here we address the possibility that intracellular ROS, regulated by the NCF4 protein (earlier often denoted p40phox) which interacts with endosomal membranes, could play an important role in the oxidation of cysteine peptides in mononuclear phagocytic cells, thereby regulating antigen presentation and activation of arthritogenic T cells. To study the role of NCF4 we used mice with an amino acid replacing mutation (NCF4R58A), which is known to affect interaction with endosomal membranes, leading to decreased intracellular ROS production. To study the impact of NCF4 on T cell activation, we used the glucose phosphate isomerase peptide GPI325-339, which contains two cysteine residues (325-339c-c). Macrophages from mice with the NCF458A mutation efficiently presented the peptide when the two cysteines were intact and not crosslinked, leading to a strong arthritogenic T cell response. T cell priming occurred in the draining lymph nodes (LNs) within 8 days after immunization. Clodronate treatment, which depletes antigen-presenting mononuclear phagocytes, ameliorated arthritis severity, whereas treatment with FYT720, which traps activated T cells in LNs, prohibited arthritis. We conclude that NCF4-dependent intracellular ROS maintains cysteine peptides in an oxidized crosslinked state, which prevents presentation of peptides recognized by non-tolerized T cells and thereby protects against autoimmune arthritis.

Human MHC Class II and Invariant Chain Knock-in Mice Mimic Rheumatoid Arthritis with Allele Restriction in Immune Response and Arthritis Association.

Transgenic mice expressing human major histocompatibility complex class II (MHCII) risk alleles are widely used in autoimmune disease research, but limitations arise due to non-physiologic expression. To address this, physiologically relevant mouse models are established via knock-in technology to explore the role of MHCII in diseases like rheumatoid arthritis. The gene sequences encoding the ectodomains are replaced with the human DRB1*04:01 and 04:02 alleles, DRA, and CD74 (invariant chain) in C57BL/6N mice. The collagen type II (Col2a1) gene is modified to mimic human COL2. Importantly, DRB1*04:01 knock-in mice display physiologic expression of human MHCII also on thymic epithelial cells, in contrast to DRB1*04:01 transgenic mice. Humanization of the invariant chain enhances MHCII expression on thymic epithelial cells, increases mature B cell numbers in spleen, and improves antigen presentation. To validate its functionality, the collagen-induced arthritis (CIA) model is used, where DRB1*04:01 expression led to a higher susceptibility to arthritis, as compared with mice expressing DRB1*04:02. In addition, the humanized T cell epitope on COL2 allows autoreactive T cell-mediated arthritis development. In conclusion, the humanized knock-in mouse faithfully expresses MHCII, confirming the DRB1*04:01 alleles role in rheumatoid arthritis and being also useful for studying MHCII-associated diseases.

NCF1-dependent production of ROS protects against lupus by regulating plasmacytoid dendritic cell development and functions.

Low capacity to produce ROS because of mutations in neutrophil cytosolic factor 1 (NCF1/p47phox), a component of NADPH oxidase 2 (NOX2) complex, is strongly associated with systemic lupus erythematosus in both humans and mouse models. Here, we aimed to identify the key immune cell type(s) and cellular mechanisms driving lupus pathogenesis under the condition of NCF1-dependent ROS deficiency. Using cell-specific Cre-deleter, human NCF1-339 variant knockin, and transgenic mouse strains, we show that low ROS production in plasmacytoid dendritic cells (pDCs) exacerbated both pristane-induced lupus and a potentially new Y-linked autoimmune accelerating locus-related spontaneous model by promoting pDC accumulation in multiple organs during lupus development, accompanied by elevated IFN-α levels and expression of IFN-stimulated genes. Mechanistic studies revealed that ROS deficiency enhanced pDC generation through the AKT/mTOR pathway and CCR2-mediated migration to tissues, which together with hyperactivation of the redox-sensitive stimulator of interferon genes/IFN-α/JAK1/STAT1 cascade further augmented type I IFN responses. More importantly, by suppressing these pathways, restoration of NOX2-derived ROS specifically in pDCs protected against lupus. These discoveries explain the causative effect of dysfunctional NCF1 in lupus and demonstrate the protective role of pDC-derived ROS in disease development driven by NCF1-dependent ROS deficiency.

A subset of antibodies targeting citrullinated proteins confers protection from rheumatoid arthritis.

Although elevated levels of anti-citrullinated protein antibodies (ACPAs) are a hallmark of rheumatoid arthritis (RA), the in vivo functions of these antibodies remain unclear. Here, we have expressed monoclonal ACPAs derived from patients with RA, and analyzed their functions in mice, as well as their specificities. None of the ACPAs showed arthritogenicity nor induced pain-associated behavior in mice. However, one of the antibodies, clone E4, protected mice from antibody-induced arthritis. E4 showed a binding pattern restricted to skin, macrophages and dendritic cells in lymphoid tissue, and cartilage derived from mouse and human arthritic joints. Proteomic analysis confirmed that E4 strongly binds to macrophages and certain RA synovial fluid proteins such as α-enolase. The protective effect of E4 was epitope-specific and dependent on the interaction between E4-citrullinated α-enolase immune complexes with FCGR2B on macrophages, resulting in increased IL-10 secretion and reduced osteoclastogenesis. These findings suggest that a subset of ACPAs have therapeutic potential in RA.

High frequency of autoantibody-secreting cells and long-lived plasma cells within inflamed kidneys of NZB/W F1 lupus mice.

Autoantibodies to double-stranded (ds) DNA represent a serological hallmark of systemic lupus erythematosus (SLE) and may critically contribute to the pathogenesis of lupus nephritis. Self-reactive antibodies might be partially produced by long-lived plasma cells (PCs), which mainly reside within the bone marrow and spleen. In contrast to short-lived PCs, long-lived PCs are extremely resistant to therapy and may sustain refractory disease courses. Recently, antibody-secreting cells were found within the inflamed kidneys of New Zealand black/white (NZB/W) F1 lupus mice as well as of patients with SLE. To analyze the longevity of the IgG-producing cells present in nephritic kidneys of NZB/W F1 mice we performed in vivo BrdU-labeling. We identified a higher frequency of long-lived than short-lived renal PCs, indicating that survival niches for long-lived PCs also exist within inflamed kidneys. Using ELISPOT assays, we found that on average 31% of renal IgG-producing cells reacted with dsDNA and 24% with nucleolin. Moreover, the frequencies of IgG-secreting cells specific for the autoantigens dsDNA and nucleolin were higher in the kidneys compared with those in the spleen and bone marrow.

Standardization of Antigen-Emulsion Preparations for the Induction of Autoimmune Disease Models.

Autoimmune murine disease models are vital tools for identifying novel targets and finding better treatments for human diseases. Complete Freund's adjuvant is commonly used to induce disease in autoimmune models, and the quality of the adjuvant/autoantigen emulsion is of critical importance in determining reproducibility. We have established an emulsification method using a standard homogenizer and specially designed receptacle. Emulsions are easy to prepare, form stable and uniform water-in-oil particles, are faster to make than the traditional syringe method, use less material and are designed to fill syringes with ease. In the present study, we have validated the emulsions for induction of experimental autoimmune encephalitis, collagen II induced arthritis, antigen induced arthritis, and delayed type hypersensitivity models. These models were induced consistently and reproducibly and, in some cases, the new method outperformed the traditional method. The method described herein is simple, cost-effective and will reduce variability, thereby requiring fewer animals for in vivo research involving animal models of autoimmune disease and in vaccine development.

Cartilage Oligomeric Matrix Protein Induced Arthritis-A New Model for Rheumatoid Arthritis in the C57BL/6 Mouse.

The most commonly used strains in experimental research, including genetically modified strains, are C57BL/6 mice. However, so far, no reliable model for rheumatoid arthritis is available, mainly due to the restriction by the MHC class II haplotype H-2b. Collagen-induced arthritis (CIA) is the most widely used animal model of rheumatoid arthritis, but C57BL/6 strain is resistant to CIA because there is no collagen II peptide associated with H-2b. To establish a rheumatoid arthritis model in C57BL/6 mice, we immunized C57BL/6NJ (B6N) mice with human cartilage oligomeric matrix protein (COMP), which induced severe arthritis with high incidence, accompanied by a strong auto-antibody response. Native COMP was required, as denatured COMP lost its ability to induce arthritis in B6N mice. An immunodominant COMP peptide was identified as the key T cell epitope, with a perfect fit into the Ab class II peptide binding pocket. A critical amino acid in this peptide was found to be phenylalanine at position 95. Recombinant COMP mutated at position 95 (COMP_F95S) lost its ability to induce arthritis or a strong immune response in the B6N mice. In conclusion, A new model for RA has been established using C57BL/6 mice through immunization with COMP, which is dependent on a COMP specific peptide binding Ab, thus in similarity with CIA in Aq expressing strains.

Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players.

Systemic lupus erythematosus (SLE) is a complex disease resulting from inflammatory responses of the immune system against several autoantigens. Inflammation is conditioned by the continuous presence of autoantibodies and leaked autoantigens, e.g. from not properly cleared dying and dead cells. Various soluble molecules and biophysical properties of the surface of apoptotic cells play significant roles in the appropriate recognition and further processing of dying and dead cells. We exemplarily discuss how Milk fat globule epidermal growth factor 8 (MFG-E8), biophysical membrane alterations, High mobility group box 1 (HMGB1), C-reactive protein (CRP), and anti-nuclear autoantibodies may contribute to the etiopathogenesis of the disease. Up to date knowledge about these key elements may provide new insights that lead to the development of new treatment strategies of the disease.

Detection and chromatographic removal of lipopolysaccharide in preparations of multifunctional galectins.

The functional spectrum of human galectins is currently explored, with a wide range of activities being described. The role of galectin-3 as adhesin for bacteria is based on its strong binding to lipopolysaccharides (LPSs), which brings the possibility of such a contamination in galectin preparations to awareness. This assumption was verified in three independent functional assay systems using polymyxin B as inhibitor of LPS-dependent effects. Moreover, a commercial LPS quantification kit also revealed LPS in galectin preparations. Chromatography was effective in removing LPS, suggesting that such a technique needs to be applied to prevent assigning cellular responses to galectins rather than LPS.

Low Production of Reactive Oxygen Species Drives Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a common autoimmune disease. Recent findings have shown that a major single nucleotide variant predisposing to SLE is associated with low production of reactive oxygen species (ROS). A variant amino acid in a frequent NCF1 allele causing deficient ROS production leads to an exaggerated type I interferon (IFN) response, earlier disease onset, and higher susceptibility to SLE. It is the so far strongest identified single nucleotide variant, with an odds ratio (OR) of >3 and an allele frequency of >10%. Its functional role is in sharp contrast to the earlier belief that excessive ROS production is exclusively pathogenic rather than protective. It opens new possibilities to understand the pathogenesis of SLE and to develop novel diagnostics and treatment strategies.

Factors masking HMGB1 in human serum and plasma.

High mobility group box 1 protein (HMGB1) is a ubiquitously expressed architectural chromosomal protein. Recently, it has become obvious that HMGB1 can also act as a proinflammatory mediator when actively secreted during cell activation or passively released from necrotic cells. HMGB1 appears to play an important role in the pathogenesis of diseases, including sepsis and rheumatoid arthritis. However, easy, sensitive, and reliable detection systems are required to investigate the clinical significance of HMGB1 in clinical samples for diagnosis and prognosis of diseases. Here, we describe sensitive ELISAs for the detection of HMGB1 in cell culture medium and cell lysates. However, these assays failed to reliably quantitate HMGB1 in serum and plasma when compared with immunoblot analysis. We found that serum/plasma components bind to HMGB1 and interfere with its detection by ELISA systems. In most serum/plasma samples investigated, including those from healthy individuals, we detected IgG antibodies binding to HMGB1. The titers of these antibodies correlated with the capacity of sera to interfere with the detection of recombinant HMGB1 by ELISA. Furthermore, HMGB1 coimmunoprecipitated with several proteins including IgG1, as identified by mass spectrometry. These HMGB1 interacting proteins are currently characterized and may contribute to complex formation, masking, and possibly, modulation of cytokine activity of HMGB1.

High mobility group box 1 in the pathogenesis of inflammatory and autoimmune diseases.

High mobility group box 1 is a nuclear protein participating in chromatin architecture and transcriptional regulation. When released from cells, HMGB1 can also act as a pro-inflammatory mediator or alarmin. Upon stimulation with lipopolysaccharides or tumor necrosis factor-alpha, HMGB1 is secreted from certain cells such as monocytes/macrophages and fosters inflammatory responses. In addition, HMGB1 is passively released from necrotic cells and mediates inflammation and immune activation. In contrast, during apoptotic cell death, nuclear HMGB1 becomes tightly attached to hypo-acetylated chromatin and is not released into the extracellular milieu, thereby preventing an inflammatory response. There is accumulating evidence that extracellular HMGB1 contributes to the pathogenesis of many inflammatory diseases, including autoimmune diseases. Increased concentrations of HMGB1 have been detected in the synovial fluid of patients with rheumatoid arthritis. In animal models of RA, HMGB1 appears to be crucially involved in the pathogenesis of arthritis since neutralization of HMGB1 significantly ameliorates the disease. Also, in the serum and plasma of patients with systemic lupus erythematosus we detected substantial amounts of HMGB1, which may contribute to the disease process. However, investigations of blood concentrations of HMGB1 and its relevance in human diseases are hindered by the lack of reliable routine test systems.

Association of NOX2 subunits genetic variants with autoimmune diseases.

A single nucleotide polymorphism in Ncf1 has been found with a major effect on chronic inflammatory autoimmune diseases in the rat with the surprising observation that a lower reactive oxygen response led to more severe diseases. This finding was subsequently reproduced in the mouse and the effect operates in many different murine diseases through different pathogenic pathways; like models for rheumatoid arthritis, encephalomyelitis, lupus, gout, psoriasis and psoriatic arthritis. The human gene is located in an unstable region with many variable sequence repetitions, which means it has not been included in any genome wide associated screens so far. However, identification of copy number variations and single nucleotide polymorphisms has now clearly shown that major autoimmune diseases are strongly associated with the Ncf1 locus. In systemic lupus erythematosus the associated Ncf1 polymorphism (leading to an amino acid substitution at position 90) is the strongest locus and is associated with a lower reactive oxidative burst response. In addition, more precise mapping analysis of polymorphism of other NOX2 genes reveals that these are also associated with autoimmunity. The identified genetic association shows the importance of redox control and that ROS regulate chronic inflammation instead of promoting it. The genetic identification of Ncf1 polymorphisms now opens for relevant studies of the regulatory mechanisms involved, effects that will have severe consequences in many different pathogenic pathways and understanding of the origin of autoimmune diseases.

Association of High Mobility Group Box Chromosomal Protein 1 and Receptor for Advanced Glycation End Products Serum Concentrations With Extraglandular Involvement and Disease Activity in Sjögren's Syndrome.

OBJECTIVE: To assess serum levels of high mobility group box chromosomal protein 1 (HMGB-1) and the soluble receptor for advanced glycation end products (sRAGE) in patients with Sjögren's syndrome (SS) and explore correlations with disease activity. METHODS: Thirty-nine patients with SS and 21 healthy controls were included in this cross-sectional study. Clinical and laboratory values were obtained from all patients. Disease activity was assessed using the European League Against Rheumatism SS Disease Activity Index (ESSDAI). Serum samples were collected and HMGB-1 and sRAGE levels were measured using enzyme-linked immunosorbent assay (ELISA), and HMGB-1 concentrations were semiquantified by Western blotting. RESULTS: In ELISA, HMGB-1 serum levels did not differ between healthy controls and patients with SS (P = 0.783). When measured by semiquantitative Western blotting, HMGB-1 levels were increased in patients with SS compared to healthy controls (P = 0.012). HMGB-1 serum levels detected by Western blotting were higher in patients with extraglandular manifestations (P = 0.003) and were correlated with ESSDAI disease activity (r = 0.544, P < 0.0001). Furthermore, sRAGE was elevated in the sera of patients with SS (P = 0.003) compared to healthy controls and was also correlated with the ESSDAI (r = 0.545, P = 0.002). CONCLUSION: Serum levels of total HMGB-1 and sRAGE were elevated in patients with SS compared to healthy controls and correlated with disease activity as measured by the ESSDAI. Patients with extraglandular involvement had high serum levels of HMGB-1.

T cells specific for post-translational modifications escape intrathymic tolerance induction.

Establishing effective central tolerance requires the promiscuous expression of tissue-restricted antigens by medullary thymic epithelial cells. However, whether central tolerance also extends to post-translationally modified proteins is not clear. Here we show a mouse model of autoimmunity in which disease development is dependent on post-translational modification (PTM) of the tissue-restricted self-antigen collagen type II. T cells specific for the non-modified antigen undergo efficient central tolerance. By contrast, PTM-reactive T cells escape thymic selection, though the PTM variant constitutes the dominant form in the periphery. This finding implies that the PTM protein is absent in the thymus, or present at concentrations insufficient to induce negative selection of developing thymocytes and explains the lower level of tolerance induction against the PTM antigen. As the majority of self-antigens are post-translationally modified, these data raise the possibility that T cells specific for other self-antigens naturally subjected to PTM may escape central tolerance induction by a similar mechanism.

Apoptotic cells selectively suppress the Th1 cytokine interferon gamma in stimulated human peripheral blood mononuclear cells and shift the Th1/Th2 balance towards Th2.

Apoptotic cells are readily recognized and engulfed by phagocytes and usually do not induce inflammation or tissue damage. Furthermore, they can actively suppress a pro-inflammatory response in phagocytes: In the presence of apoptotic cells, activated monocytes/macrophages produce more of the anti-inflammatory and immunoregulatory cytokines IL-10 and TGF-beta, but less of the pro-inflammatory cytokines TNFalpha, IL-1beta and IL-12. This immunoregulatory effect is most likely mediated by several receptors on monocytes/macrophages including the thrombospondin receptor (CD36). In addition to the modulation of cytokine secretion, apoptotic cell material inhibited the expression of MHC class II molecules on the surface of monocytes/macrophages. Decreased MHC II expression appeared to be mediated predominantly by increased IL-10 secretion in a para-/autocrine manner. Here, we show that the functional modulation of antigen-presenting monocytes/macrophages by apoptotic cells also influences T cell activation and function. When human peripheral blood mononuclear cells were stimulated with recall antigens in the presence of apoptotic cells, interferon gamma (IFN gamma) secretion was markedly suppressed, whereas secretion of the Th2 cytokine IL-4 was not significantly altered. Hence, apoptotic cells shift the T cell cytokine secretion pattern towards a Th2-like response. This Th2 shift can largely be prevented by neutralizing IL-10, indicating an important role of this cytokine for modulating T cell cytokine secretion patterns.

Sensitive detection of plasma/serum DNA in patients with systemic lupus erythematosus.

OBJECTIVE: To optimize the use of the fluorochromic PicoGreen assay for the sensitive detection and quantification of double stranded (ds) DNA in plasma/serum samples of patients with systemic lupus erythematosus (SLE). METHODS: Plasma/serum samples were obtained from SLE patients and normal healthy donors (NHD). Plasma/serum proteins were digested with proteinase K. DNA was subsequently purified using silica-based ion exchange micro columns and detected using the PicoGreen assay. RESULTS: Sensitive detection of plasma/serum DNA is impaired by proteins: (1) Proteins caused background fluorescence in the PicoGreen assay. (2) Packaging of dsDNA in nucleosomes markedly reduced PicoGreen fluorescence. Therefore, we digested proteins using proteinase K and purified DNA before detection by PicoGreen assay. This procedure resulted in a detection limit for plasma/serum dsDNA of less than 1 ng/ml, and is therefore markedly more sensitive than previously described methods. We found that DNA concentrations are higher in serum than in plasma of healthy donors, suggesting artifactual DNA release during coagulation. In addition, we found higher levels of DNA in plasma and serum of a group of SLE patients compared to NHD. CONCLUSIONS: We have optimized the use of the PicoGreen assay for the ultrasensitive and reliable quantification of DNA in plasma/serum samples. This new method can be used in future studies to explore a possible correlation between circulating DNA levels and disease activity in patients with SLE.