Circulating DNA and lupus nephritis

Analysis of circulating tumor DNA in breast cancer as a diagnostic and prognostic biomarker

Despite all the advances in diagnosis and treatment of breast cancer, a large number of patients suffer from late diagnosis or recurrence of their disease. Current available imaging modalities do not reveal micrometastasis and tumor biopsy is an invasive method to detect early stage or recurrent cancer, signifying the need for an inexpensive, non-invasive diagnostic modality. Cell-free tumor DNA (ctDNA) has been tried for early detection and targeted therapy of breast cancer, but its diagnostic and prognostic utility is still under investigation. This review summarizes the existing evidence on the use of ctDNA specifically in breast cancer, including detection methods, diagnostic accuracy, role in genetics and epigenetics evaluation of the tumor, and comparison with other biomarkers. Current evidence suggests that increasing levels of ctDNA in breast cancer can be of significant diagnostic value for early detection of breast cancer although the sensitivity and specificity of the methods is still suboptimal. Additionally, ctDNA allows for characterizing the tumor in a non-invasive way and monitor the response to therapy, although discordance of ctDNA results with direct biopsy (i.e. due to tumor heterogeneity) is still considered a notable limitation.

Mixed connective tissue disease developing into MPO-ANCA-positive polyangiitis

Renal involvement of mixed connective tissue disease (MCTD) shows systemic lupus erythematosus (SLE)-like immune complex glomerulonephritis. The prognosis of this condition is generally good. We report the case of an elderly female patient with MCTD who developed autoimmune pleurisy and rapidly progressive glomerulonephritis. Myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA) was positive with a titer of 59.0 EU. Anti-DNA antibody and complement levels were normal. Renal biopsy revealed crescentic glomerulonephritis and mild mesangial proliferation. However, immunofluorescence examination revealed immune-complex glomerulonephritis. These findings suggest that the renal involvement of MCTD developed concurrently with MPO-ANCA-related glomerulonephritis.

Identification of new pathogenic players in lupus: autoantibody-secreting cells are present in nephritic kidneys of (NZBxNZW)F1 mice

An important hallmark of systemic lupus erythematosus is the production of autoantibodies specific for nuclear Ags, among which nucleosomes and their constituents, DNA and histones. It is widely admitted that some of these autoantibodies contribute largely in lupus pathogenesis because of their nephritogenic potential. However, the underlying mechanisms are still debated. In this study, we analyzed the autoimmune response against histone H2B during the course of the disease in lupus-prone (NZBxNZW)F1 mice, both in lymphoid organs and kidneys, and we assessed its potential involvement in lupus pathogenicity. We found that the N-terminal region of histone H2B represents a preferential target for circulating autoantibodies, which kinetics of appearance positively correlates with disease development. Furthermore, immunization of preautoimmune (NZBxNZW)F1 mice with H2B peptide 1-25 accelerates the disease. Kidney eluates from diseased (NZBxNZW)F1 mice do contain IgG Abs reacting with this peptide, and this H2B sequence was found to be accessible to specific Ab probes in Ag-containing deposits detected in nephritic kidneys. Finally, compared with control normal mice and to young preautoimmune (NZBxNZW)F1 animals, the frequency of cells secreting autoantibodies reacting with peptide 1-25 was significantly raised in the spleen and bone marrow and most importantly on a pathophysiological point of view, locally, in nephritic kidneys of diseased (NZBxNZW)F1 mice. Altogether our results demonstrate the existence in (NZBxNZW)F1 mice of both a systemic and local B cell response targeting the N-terminal region of histone H2B, and highlight the potential implication of this nuclear domain in lupus pathology.

Pathogenic anti-nucleosome antibodies

There is increasing evidence that in systemic lupus erythematosus, nucleosomes, the basic chromatin component, represent both a driving immunogen and a major in vivo target for antibodies. Either a disturbed apoptosis or a reduced clearance of apoptotic cells by phagocytes may lead to an increased exposure of apoptotic nucleosomes to the immune system. These nucleosomes, which have been cleaved and modified during the process of apoptosis, escape normal clearance and encompass epitopes that normally are not encountered by the immune system. This may then lead to tolerance breaking and autoimmunity by the activation of nucleosome-specific autoreactive T cells (that help B cells) and subsequently to the production of anti-nucleosome, anti-histone and anti-DNA autoantibodies. Some anti-nucleosome antibody subsets are pathogenic and are involved in the nephritogenic process in systemic lupus erythematosus. Accordingly, several studies reported: (i) increased plasma circulating nucleosomes that positively correlated with an active disease, (ii) nucleosomes in typical glomerular deposits as well as in the basement membrane of non-lesional skin of systemic lupus erythematosus patients and (iii) a close correlation between nephritis and the presence of anti-nucleosome antibodies. Recent studies reported anti-nucleosome antibodies also in primary anti-phospholipid syndrome and particularly in patients with associated lupus-like disease.

Cuts can kill: the roles of apoptotic nucleases in cell death and animal development

Chromosome fragmentation is one of the major biochemical hallmarks of apoptosis. However, until recently, its roles in apoptosis and mechanisms of action remained elusive. Recent biochemical and genetic studies have shown that chromosome fragmentation is a complex biochemical process that involves a plethora of conserved nucleases with distinct nuclease activities and substrate specificities. These apoptotic nucleases act cooperatively among themselves and with other nonnuclease cofactors to promote stepwise chromosome fragmentation and DNA degradation. Importantly, in addition to its direct contribution to the dismantling of the dying cell, apoptotic DNA degradation can facilitate cell killing and other apoptotic events such as clearance of apoptotic cells. Furthermore, some apoptotic nucleases apparently affect other aspects of animal development, including immune responses. The identification of new apoptotic nucleases and analysis of their functions in apoptosis and animal development should pave the way for future studies to uncover new functions for apoptotic nucleases and shed light on the hidden links between apoptotic DNA degradation and human diseases.

Pathogenesis of lupus nephritis: an update

Lupus nephritis (LN) is a prototypic autoimmune disease. Its immunopathogenesis is characterized by the loss of self-tolerance. In this article, we review our current understanding of the disease mediators of LN. There is ample evidence to suggest a pathogenic role of nephritogenic autoantibodies. These antibodies cross react with nucleosomal epitopes, and the in vivo generation of nucleosomes requires apoptosis. Furthermore, there is an intriguing and paradoxical relationship between complement and systemic lupus erythematosus (SLE). Immune complex-mediated activation of complement through the classic pathway is traditionally believed to be a major mechanism by which tissue injury occurs. In contrast, hereditary deficiencies of complement components increase the risk of SLE. Finally, the roles of reactive nitrogen and oxygen species are emphasized.

Pathology of lupus nephritis

The glomerular pathology of lupus nephritis is the result of diverse immune insults which are probably of independent pathogenetic origins. Although lupus nephritis is looked upon as a classic example of immune complex-induced microvascular injury resulting from circulating DNA double stranded polynucleotide antigens/anti-DNA antibody complexes, other mechanisms, including in situ reactivity of free antibody with fixed antigens and the role of sensitized T-cells, are probably an important part of the picture. This complexity makes categorization of glomerular pathology into a clinically relevant classification an important goal so that our experiences can be reliably compared. This review describes the various glomerular lesions commonly encountered in lupus nephritis and, based upon data derived from experimental models, emphasizes the importance of understanding the clinical relevance of the reported morphology. We point out that the severity of glomerular damage is not merely the accrued result of immune complex induced injury to individual capillaries, but involves capillary necrosis and thrombosis, neither of which may have anything to do with immune complexes or immune aggregates. In fact, the segmental lesions of glomerular capillary necrosis and thrombosis may have a great deal to do with the response to therapy and the ultimate outcome of the patient. While discrete morphologic lesions such as mesangiopathy, acute inflammation, necrosis, thrombosis, epimembranous lesions and podocytopathy are readily described, it is important to note that any given case can represent any combination of these insults. In this context, the new proposed International Society of Nephrology Classification is presented and its strengths and weaknesses discussed.

The effect of inflammation on the generation of plasma DNA from dead and dying cells in the peritoneum

To assess the effects of inflammation on the generation of circulating DNA from dead and dying cells, plasma DNA levels were determined in BALB/c mice, administered apoptotic or necrotic Jurkat cells following induction of peritonitis by treatment with thioglycollate (TG), peptone (PT), or sodium periodate (NaIO(4)). In mice receiving TG or NaIO(4), plasma DNA levels following intraperitoneal administration of Jurkat cells were significantly reduced compared with controls, whereas they were not affected in mice receiving PT. To determine the basis of these differences, the cellular composition of peritoneal fluids prior to the administration of the dead cells was analyzed. Among agents tested, TG administration led to the largest increase in cells, both neutrophils and monocytes. As shown by flow cytometry, the exudates contained apoptotic neutrophils and macrophages, with the highest levels in the TG-induced exudates. Analysis of DNA and caspase 3 in the fluids also showed differences. TG exudates showed increases in DNA and caspase 3, while NaIO(4)-induced exudates had an increase only in DNA. Fluid from PT-treated mice did not have increases in DNA or caspase 3. Together, these results indicate that prior inflammation can affect the generation of blood DNA from apoptotic or necrotic cells, although this effect may vary depending on the composition of the exudates with respect to cells as well as DNA.

The immune response to cell death in SLE

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antinuclear antibodies (ANA). These antibodies target a wide variety of antigens whose presence in an immunologically active form may result from cell death processes that cause their translocation and release from cells. As indicated by in vivo model systems, the release of DNA from cells may not be a simple consequence of cell death but rather may require the intervention of other cell types including macrophages. Thus, in mice, administration of either apoptotic or necrotic cells produces a blood DNA response, whereas mice lacking macrophages fail to show blood DNA under the same conditions. Furthermore, the circulating DNA arising from apoptotic and necrotic cells displays a similar pattern with respect to size distribution, with both showing DNA laddering, a pattern indicating enzymatic cleavage. Since circulating DNA in the form of immune complexes can play a role in lupus pathogenesis, these findings suggest that the generation and clearance of dead cells are important events that may underlie autoimmunity in this disease and may be targeted for therapy.

Release of DNA from dead and dying lymphocyte and monocyte cell lines in vitro

DNA is a nuclear macromolecule that circulates in the blood where its levels can reflect the activity of inflammatory and malignant diseases. While dead and dying cells have usually been considered the source of blood DNA, the mechanisms for its release during apoptosis and necrosis are not well defined. To elucidate DNA release, an in vitro model system was used, assessing DNA in the media of living, apoptotic or necrotic Jurkat and U937 cells. Apoptosis was induced by etoposide, camptothecin or staurosporine, while necrosis was induced by heating at 56 degrees C. DNA release was measured by fluorometry with the dye PicoGreen while the extent of death was measured by fluorescence-activated cell sorter analysis with propidium iodide and annexin. Apoptotic Jurkat cells released significantly more DNA in the media than untreated cells while necrotic cells did not show significant DNA release. U937 cells showed similar findings. Pretreatment of Jurkat cells with z-VAD-fmk, a caspase inhibitor, reduced both apoptosis and DNA release. By gel electrophoresis, extracellular DNA from apoptotic cells showed laddering with low molecular weight fragments. These studies suggest that extracellular release of DNA is a consequence of apoptosis and may account for some of the DNA in the blood.

New approaches to the renal pathogenicity of anti-DNA antibodies in systemic lupus erythematosus

Autoantibodies against double stranded (ds) DNA are not only a helpful serological marker for diagnosis of systemic lupus erythematosus (SLE), but have also been shown to be crucial in the pathogenesis of lupus nephritis. However, the question of how anti-dsDNA antibodies contribute to renal damage is unresolved. Many authorities believe that indirect binding (mediated by nuclear antigens) or direct cross-reactivity of anti-dsDNA antibodies with kidney antigens are important determinants of anti-dsDNA nephritogenicity. An alternative hypothesis for the renal pathogenicity of anti-dsDNA antibodies was proposed more than 20 years ago, namely that certain autoantibodies could penetrate into living cells and thus induce damage. Work from several laboratories has recently provided firm support for this iconoclastic theory, which contradicted prevailing immunologic dogma that cell interiors are inaccessible to antibodies. Here, we review the evidence that anti-dsDNA antibodies may penetrate into living cells, and discuss which intracellular events may follow from binding of anti-dsDNA antibodies to the cell surface and subsequent intracellular penetration. Determining the mechanism by which anti-dsDNA antibodies induce renal injury is important for understanding a major disease manifestation of lupus, and may lead to the development of novel approaches to the treatment of lupus renal disease.

CD4+ T cells from (New Zealand Black x New Zealand White)F1 lupus mice and normal mice immunized against apoptotic nucleosomes recognize similar Th cell epitopes in the C terminus of histone H3

We have previously reported that peptide 88-99 of histone H4 represents a minimal T cell epitope recognized by Th cells from nonautoimmune BALB/c (H-2(d/d)) mice immunized with nucleosomes. In this study, we tested a panel of overlapping peptides spanning the whole sequences of H4 and H3 for recognition by CD4(+) T cells from unprimed (New Zealand Black (NZB) x New Zealand White (NZW))F(1) lupus mice (H-2(d/z)). None of the 11 H4 peptides was recognized by CD4(+) T cells from (NZB x NZW)F(1) mice. In contrast, these cells proliferated and secreted IL-2, IL-10, and IFN-gamma upon ex vivo stimulation with H3 peptides representing sequences 53-70, 64-78, and 68-85. Peptides 56-73 and 61-78 induced the production of IFN-gamma and IL-10, respectively, without detectable proliferation, suggesting that they may act as partial agonist of the TCR. Th cells from unprimed BALB/c mice and other lupus-prone mice such as SNF(1) (H-2(d/q)) and MRL/lpr (H-2(k/k)) mice did not recognize any peptides present within the H3 region 53-85. We further demonstrated that immunization of normal BALB/c mice with syngeneic liver nucleosomes and spleen apoptotic cells, but not with nonapoptotic syngeneic cells, induced Th cell responses against several peptides of the H3 region 53-85. Moreover, we found that this conserved region of H3, which is accessible at the surface of nucleosomes, is targeted by Abs from (NZB x NZW)F(1) mice and lupus patients, and contains motifs recognized by several distinct HLA-DR molecules. It might thus be important in the self-tolerance breakdown in lupus.

Antigenic triggers and molecular targets for anti-double-stranded DNA antibodies

While anti-double-stranded (ds)DNA antibodies are a characteristic serologic hallmark for SLE, the triggering antigen is unknown. Using phage display libraries, we identified DWEYSVWLSN as a peptide mimic of DNA for a pathogenic anti-dsDNA antibody. Peptide immunization of non-autoimmune mice induced anti-dsDNA as well as other lupus-associated antibodies. Molecular analysis of the induced anti-dsDNA antibodies revealed several similarities with anti-dsDNA antibodies that appear spontaneously in lupus mice. Furthermore, lupus-prone mice immunized with this peptide DNA mimic had higher autoantibody titers as well as more severe nephritis. Anti-DNA antibodies may contribute to lupus nephritis via cross-reactivity with renal antigen. Using western blotting of lysates of mesangial cells from a lupus mouse, we found that a pathogenic anti-DNA antibody binds to alpha-actinin. High titers of anti-alpha-actinin antibodies were present in the sera and kidney eluates of lupus mice with active disease. Binding to alpha-actinin was diminished in mesangial cells derived from BALB/c mice, suggesting that target antigen expression may play a role in determining autoantibody binding to the kidney. We conclude that a pathogenic, lupus-like autoantibody response can be induced by a peptide antigen, and that alpha-actinin is a cross-reactive renal target for the pathogenic anti-dsDNA autoantibody response in lupus mice.

The use of fluorometric assays to assess the immune response to DNA in murine systemic lupus erythematosus

Antibodies to DNA (anti-DNA) play an important role in the pathogenesis of systemic lupus erythematosus (SLE). In blood, these antibodies may exist in a free, unbound state or as part of complexes with DNA. Furthermore, circulating DNA may be either complexed or free. Because of the central role of these immunoreactants (anti-DNA and DNA) in the disease, monitoring of their levels could provide valuable information for both clinical and investigative purposes. In these studies, we have explored the use of a DNA-binding dye, PicoGreen, for the detection of circulating DNA, either total or immune complex bound. In addition, we have used this dye for Farr-type antibody assays. Using autoimmune MRL/lpr mice as a model, we have shown that, while the levels of free DNA in the plasma of these mice were comparable with those of normal BALB/c mice, the amounts in complexes precipitable by ammonium sulfate were significantly greater. Furthermore, we showed that Farr assays using PicoGreen reliably detect levels of free anti-DNA, with values correlated with anti-DNA levels by an enzyme-linked immunosorbent assay. Together, our results suggest that a fluorometric dye can accurately monitor DNA and anti-DNA antibody levels in SLE and may provide important information on immunopathogenesis.

Functional genomic analysis of apoptotic DNA degradation in C. elegans

Chromosomal DNA degradation is critical for cell death execution and is a hallmark of apoptosis, yet little is known about how this process is executed. Using an RNAi-based functional genomic approach, we have identified seven additional cell death-related nucleases (crn genes), which along with two known nucleases (CPS-6 and NUC-1) comprise at least two independent pathways that contribute to cell killing, and likely signaling for phagocytosis, by degrading chromosomal DNA. Several crn genes have human homologs that are important for RNA processing, protein folding, DNA replication, and DNA damage repair, suggesting dual roles for CRN nucleases in cell survival and cell death. It should now be possible to systematically decipher the mechanisms of apoptotic DNA degradation.

Immune homeostasis requires several biologic factors including glucocorticoid hormones

Immunological tolerance can be achieved by several mechanisms including suppressor cells, soluble factors, and neurohormonal mediators. On the cellular level, we isolated a population of CD8+CD28- T cells capable of inhibiting anti-CD3 mAb-induced proliferation of autologous peripheral blood mononuclear cells in an HLA-I nonrestricted manner via production of IFN-gamma and IL-6. Interestingly, CD8+CD28- T cells from systemic lupus erythematosus patients with active disease do not display this inhibitory activity and show a marked imbalance between inhibitory (IL-6) and stimulatory (IL-12) cytokines. For soluble factors, we studied soluble HLA molecules (sHLAs) and double-stranded DNA (ds-DNA). Soluble HLA-I (sHLA-I) molecules induce soluble Fas ligand (sFasL) secretion and trigger apoptosis in phytohemagglutin (PHA)-activated Fas+ T cells. Double-stranded DNA binds to HLA-II molecules and inhibits HLA-II-mediated antigen presentation. On the neurohormonal side, we focused our attention on the immunological activity of corticosteroids (CTSs). CTSs inhibit recirculation of CD4+ T cells, suppress the proliferation and immunological function of activated T cells, and induce apoptosis of activated lymphocytes. Taken together, these data suggest the presence of a complex network of immunoregulatory mechanisms in which CTSs play a strong role supporting their recognized efficacy in the treatment of inflammatory and immunological diseases.

Nucleosomes in serum of patients with benign and malignant diseases

High quantities of mono- and oligonucleosomes circulate in the blood of patients with malignant tumors. For their direct quantification in serum, we modified the Cell Death Detection(plus)-ELISA for its application in liquid materials. We examined sera samples from 590 persons, including 418 patients with malignant tumors, 109 patients with benign diseases and 63 healthy persons. We also observed the kinetics of the concentration of nucleosomes in serum samples from 20 patients undergoing chemotherapy and from 16 patients undergoing radiotherapy. Sera of patients with malignant tumors contained considerably higher concentrations of nucleosomes (mean = 350 arbitrary units [AU], median = 190 AU) compared with those of healthy persons (mean = 36 AU, median = 24 AU; p = 0.0001) and patients with benign diseases (mean = 264 AU, median = 146 AU; p = 0.072). Concerning the follow-up investigations, the concentration of nucleosomes in serum increased 24-72 hr after the first application of chemotherapy and 6-24 hr after the start of radiotherapy. A subsequent decrease was often correlated with regression of the tumor. In patients undergoing chemotherapy, an increase in the baseline values of circulating nucleosomes >50%, which were determined before each new therapeutic cycle, was correlated with progression of disease; all patients with disease regression showed a decrease >50% of the baseline values. In patients undergoing radiotherapy, an early decrease of the nucleosomal concentration (< or = 1 day after the initial peak during therapy) to low minimum levels (< or = 100 AU) correlated with good clinical outcome; a late decrease (>1 day) to higher minimum levels (>100 AU) was associated with a worse clinical outcome. Thus, the concentration of nucleosomes in serum might be a useful tool for monitoring the biochemical response during antitumor therapy, especially for the early estimation of therapeutic efficacy.

Plasma Nucleosome Levels in Node-Negative Breast Cancer Patients

BACKGROUND: A nucleosome is a primary repeating unit of organized DNA in chromatin, and cell death may lead to increased levels of circulating nucleosomes inplasma (PNLs) in various circumstances such as inflammation, pulmonary embolism, autoimmune disease and cancer. MATERIALS AND METHODS: We investigated PNLs in 96 patients with stage 0-III breast cancer (node-negative, n =57; node-positive, n=39), and in 111 women without any evidence of disease as healthy controls. PNLs were detected using the Cell Death Detection ELISAplus kit (Boehringer Mannheim, Japan). RESULTS: The PNLs in normal controls were 0.010 +/- 0.012 units (mean +/- SD), while PNLs were significantly higher in both node-negative breast cancer (0.153 +/- 0.242) and node-positive breast cancer patients (0.116 +/- 0.172) (p <0.01). When PNLs were classified as high (>0.10) and low( </=0.10), no correlation was found between high PNLs and clinicopathological factors such as tumor size, menopausal status, estrogen receptor status, histological type and lymphatic or venous spread in node-negative breast cancer. The relapse-free survival of patients with high PNLs tended to be better than those with low PNLs in both node-negative and node-positive breast cancer. CONCLUSION: Increased PNLs were found in breast cancer patients, and PNLs seem promising as a new prognostic factor for both node-negative and node-positive breast cancer.

Abnormal DNA methylation and deoxycytosine-deoxyguanine content in nucleosomes from lymphocytes undergoing apoptosis

Systemic lupus erythematosus (SLE) is characterized by an accelerated apoptosis of peripheral lymphocytes and an impairment of the clearance of apoptotic cells. Since changes in DNA methylation and in deoxycytosine and deoxyguanine (GC) content have been shown to enhance the potential of DNA to activate murine and human B lymphocytes, we tested the capacity of lymphocytes undergoing apoptosis (under conditions that mimic the deletion of self-reactive cells after antigen receptor engagement) to generate nucleosomes with a particular base composition. Using two cell culture systems and four apoptosis triggers, we found an increase of deoxymethylcytosine in fragmented chromosomal DNA of apoptotic B and T lymphocytes. However, this increase was not associated with modulation of DNA (cytosine-5) methyltransferase, the enzyme that methylates eukaryotic DNA, which suggests that the changes in DNA methylation patterns are not linked to the process of de novo DNA methylation during cell death. In addition, we could not detect a unique methylation pattern in highly repetitive Alu sequences present in the human genome of SLE subjects, as compared with controls. However, the abnormal DNA methylation of apoptotic nucleosomes was associated with an unusual pattern of nuclease-resistant, GC-rich regions in these DNA fragments. We propose that the combination of an accelerated apoptosis with a defect in the clearance of apoptotic cells results in release of increased amounts of nucleosomes with abnormally methylated, GC-rich DNA and provides an autologous stimulation that could bypass tolerance to self in systemic autoimmune diseases. These findings support the concept that the structure and dynamics of nucleosomes are critical in determining their immunogenicity in SLE.

Double-stranded deoxyribonucleic acid binds to HLA class II molecules and inhibits HLA class II-mediated antigen presentation

CD4+ T cells proliferating in response to purified double-stranded deoxyribonucleic acid (dsDNA) have been recently demonstrated in peripheral blood mononuclear cells of patients with systemic lupus erythematosus. Their activation was inhibited by anti-HLA class II (HLA-II) monoclonal antibodies; thus, the existence of a molecular interaction between dsDNA and HLA-II is conceivable. In this report we show that dsDNA specifically bind to HLA-II. After preincubating cells with purified dsDNA or synthetic oligonucleotides, dsDNA was detected on the cell membrane and in the lysates of HLA-II+ but not of isogenic HLA-II- cell lines. We demonstrate that dsDNA binding inhibits that of a specific peptide to HLA-II. Mixed lymphocyte reaction and antigen-specific T cell proliferation were inhibited by the preincubation of stimulator cells or antigen-presenting cells with dsDNA. These results suggest the existence of a novel mechanism of down-modulation of the CD4+ T cell function generated by lack of stimulation due to the HLA-II presenting molecules being "occupied" by dsDNA.

Expression of decay accelerating factor mRNA and complement C3 mRNA in human diseased kidney

BACKGROUND

Decay accelerating factor (DAF), a product of mesangial cells in vitro, is expressed on the surface of cells and is a candidate for the focal suppression of complement activation. It is not clear at present whether the levels of expression of DAF and intrarenal C3 synthesis correlate with the level of tissue injury.

METHODS

Immunohistochemistry for DAF and C3 and nonradioactive in situ hybridization with digoxigenin-labeled oligonucleotide probe for DAF and C3 mRNA were performed in 22 tissue samples of kidneys from patients with IgA nephropathy (IgAN), 6 with membranous nephropathy (MN), 6 with lupus nephritis (LN), and five normal kidneys.

RESULTS

In the normal kidney, DAF was confined to the juxtaglomerular apparatus and little or no C3 was detected; however, a few glomerular cells were positive for DAF mRNA but no C3 mRNA positive cells were detected. In diseased kidneys, DAF and C3 as well as their mRNAs were detected in mesangial cells, tubular cells and infiltrating cells. Glomerular epithelial cells and Bowman's capsule cells contained little or no DAF and C3 but were positive for their mRNAs. The mean percentages of mesangial cells positive for DAF and C3 mRNAs were 49.3 +/- 11.5% and 50.7 +/- 10.3% in IgAN, and 17.0 +/- 6.3% and 19.4 +/- 9.0% in MN, respectively. The percentage of mesangial cells positive for DAF and C3 mRNAs among intraglomerular cells correlated positively with the degree of mesangial proliferation and glomerular sclerosis in IgAN. In contrast, in LN the percentage of glomerular cells positive for DAF mRNA correlated negatively with the degree of glomerular injury, while the percentage of cells positive for C3 mRNA did not change with the progression of the disease. The ratio of C3 mRNA/DAF mRNA of glomerular cells correlated with the degree of glomerular injury in both IgAN and LN. In the tubulointerstitium, the percentage of cells expressing mRNA, and C3 mRNA/DAF mRNA radio correlated with the degree of tubular atrophy and interstitial broadening in both IgAN and LN.

CONCLUSIONS

We conclude that DAF and C3 mRNAs are synthesized in human diseased kidneys, and that a balance between locally synthesized DAF and C3 may be important in the progression of glomerulonephritis.

Circulating plasma levels of nucleosomes in patients with systemic lupus erythematosus: correlation with serum antinucleosome antibody titers and absence of clear association with disease activity

OBJECTIVE

To assess nucleosome plasma levels in patients with systemic lupus erythematosus (SLE) and to study the correlations with serum antinucleosome, anti-double-stranded DNA (anti-dsDNA), and antihistone antibody activities, as well as with disease activity (by the SLE Disease Activity Index [SLEDAI]).

METHODS

In a cross-sectional study, we assessed 58 SLE patients for their plasma nucleosome levels. Plasma nucleosome levels as well as serum antinucleosome, anti-double-stranded DNA, and antihistone antibody activities were assessed by enzyme-linked immunosorbent assay. SLE activity was evaluated using the SLEDAI:

RESULTS

The mean (+/-SD) plasma nucleosome concentration in SLE patients was 52 +/- 159 ng/ml (range 5-1,180), and was significantly higher than that of the controls (16 +/- 8.8 ng/ml, range 8-52; P = 0.03). Thirteen of the 58 lupus patients had levels over the range of normal (defined as the control mean + 3 SD, or 42 ng/ml). An inverse correlation was found between nucleosome plasma levels and serum antinucleosome antibody activity in the entire group of SLE patients, those with active disease, and those with inactive disease, respectively. No correlation was found between the SLEDAI and nucleosome plasma concentrations.

CONCLUSION

Nucleosome plasma levels may be normal or increased in SLE, and found in patients with active or inactive SLE. Longitudinal studies are needed to further establish whether high levels of circulating nucleosomes may predict the occurrence of an SLE flare.

Antigen specificity of anti-nuclear antibodies complexed to nucleosomes determines glomerular basement membrane binding in vivo

Monoclonal anti-nuclear antibodies which are complexed to nucleosomes are able to bind to the glomerular basement membrane (GBM) in vivo, whereas purified antibodies do not bind. The positively charged histone moieties in the nucleosome are-responsible for the binding to anionic determinants in the GBM. We tested the hypothesis that the specificity of the autoantibodies complexed to the nucleosome influences the glomerular binding of the antibody-nucleosome complex. We induced the formation of these immune complexes in vivo, by intraperitoneal inoculation of hybridomas producing monoclonal anti-nuclear antibodies (four anti-histone, three anti-double stranded (ds)DNA and three anti-nucleosome antibodies) into nude BALB/c mice. In ascites and plasma from the mice inoculated with these hybridomas, nucleosome/autoantibody complexes were detected in comparable amounts. Immunofluorescence of kidney sections revealed that about 60% of the mice inoculated with anti-nucleosome or anti-dsDNA hybridomas had immunoglobulin deposits in the GBM, whereas only 15% of the mice with anti-histone hybridomas showed these deposits (p < or = 0.04). In the Matrigel-ELISA (used as a GBM surrogate) ascites from anti-nucleosome or anti-DNA hybridomas displayed significantly higher titers (p < or = 0.002) than ascites from anti-histone hybridomas. In conclusion, nucleosome/immunoglobulin complexes comprising anti-nucleosome or anti-dsDNA auto-antibodies do bind more frequently to the GBM in vivo than nucleosome/immunoglobulin complexes containing anti-histone antibodies. It therefore appears that the specificity of the antibody bound to the nucleosome is a critical determinant for the nephritogenic potential of the nucleosome-autoantibody complex.

Soluble oligonucleosomal complexes in synovial fluid from inflamed joints

OBJECTIVE

To determine whether soluble oligonucleosomal DNA, typical of that released during apoptotic cell death, is present in synovial fluids from inflamed joints and, if so, whether it is present in sufficient concentrations to have pathophysiologic significance.

METHODS

Fifty synovial fluid specimens from 46 patients were studied, 41 from joints with a variety of inflammatory disorders and 9 from osteoarthritic joints. DNA from freshly collected synovial fluid was isolated and quantitated by microfluorometry, and the oligonucleosomal fraction was measured by radiolabeling, gel electrophoresis, and autoradiography. Specific immunoprecipitation with monoclonal antihistone antibody, after DNA radiolabeling in whole synovial fluid, was used to detect histone binding.

RESULTS

DNA with a typical oligonucleosomal ladder was observed in most specimens. The mean +/- SD oligonucleosomal DNA concentration was 14.1 +/- 18.5 microg/ml in synovial fluids from inflamed joints, considerably higher than that in osteoarthritic synovial fluids. Additionally, the DNA was shown to be complexed with histone, as would be expected. Control experiments were performed to show that the oligonucleosomal DNA was present in soluble form and did not arise due to in vitro artifact. The DNA concentrations were found to correlate significantly with the concentrations of synovial fluid leukocytes, most of which were neutrophils.

CONCLUSION

Synovial fluids from inflamed joints contain oligonucleosomal DNA typical of that released during apoptotic cell death. The probable source is fluid-phase neutrophils undergoing apoptotic cell death, although this was not directly demonstrated. The concentrations are sufficient to have biologic activity similar to that shown in vitro, including lymphoproliferation and stimulation of interleukin-6 secretion. A mechanism by which oligonucleosomal DNA may contribute to perpetuation of rheumatoid synovitis is proposed. If it is generalizable to other sites of inflammation, as seems probable, similar oligonucleosomal DNA release accompanying inflammation may play a pathogenetic role in other disorders, including systemic lupus erythematosus.

The double edged sword of the immune response: mutational analysis of a murine anti-pneumococcal, anti-DNA antibody

Anti-double-stranded (ds) DNA antibodies are not only an important diagnostic marker for SLE, but also play an important role in tissue injury. Microbial antigen may be a stimulus for the production of these antibodies. We isolated 99D.7E, an IgG2b monoclonal antibody from a nonautoimmune BALB/c mouse that is cross-reactive with both dsDNA and phosphorylcholine, the dominant hapten on the pneumococcal cell wall. While partially protective against a bacterial challenge, 99D.7E is also pathogenic to the kidney. To identify those molecular motifs that confer on anti-PC antibodies the potential for autoreactivity, we created a panel of 99D.7E mutants with single amino acid substitutions in the heavy chain, and examined the changes in antigen binding and renal deposition. Our results support the hypothesis that charge and affinity for dsDNA are not adequate predictors of the pathogenicity of anti-DNA antibodies. Differential renal damage from anti-dsDNA antibodies may be due to differences in fine specificity, rather than differential affinity for dsDNA. Importantly, high affinity IgG antibodies cross-reactive with bacterial and self antigen exist and can display pathogenic potential, suggesting that defects in peripheral regulation of B cells, activated by foreign antigen but cross-reactive with self antigen, might lead to autoimmune disorders.

Ligand recognition by murine anti-DNA autoantibodies. II. Genetic analysis and pathogenicity

Although anti-DNA autoantibodies are an important hallmark of lupus, the relationships among anti-DNA structure, reactivity, and pathogenicity have not been fully elucidated. To further investigate these relationships, we compare the variable genes and primary structure of eight anti-DNA mAbs previously obtained from an MRL/MpJ-lpr/lpr mouse along with the ability of three representative mAbs to induce nephritis in nonautoimmune mice using established adoptive transfer protocols. One monospecific anti-single-stranded (ss) DNA (11F8) induces severe diffuse proliferative glomerulonephritis in nonautoimmune mice whereas another anti-ssDNA with apparently similar in vitro binding properties (9F11) and an anti-double-stranded DNA (4B2) are essentially benign. These results establish a murine model of anti-DNA-induced glomerular injury resembling the severe nephritis seen in lupus patients and provide direct evidence that anti-ssDNA can be more pathogenic than anti-double-stranded DNA. In vitro binding experiments using both protein-DNA complexes and naive kidney tissue indicate that glomerular localization of 11F8 may occur by recognition of a planted antigen in vivo. Binding to this antigen is DNase sensitive which suggests that DNA or a DNA-containing molecule is being recognized.

Increased release of von Willebrand factor antigen from endothelial cells by anti-DNA autoantibodies

OBJECTIVE

To determine whether antibodies to double stranded DNA (anti-dsDNA) have a pathogenic role in systemic lupus erythematosus (SLE).

METHODS

IgG was purified from 17 patients with SLE (median anti-dsDNA titre 1212 IU/ml) and nine healthy controls (median titre 40 IU/ml). Anti-dsDNA depleted polyclonal IgG (median anti-dsDNA titre 17 IU/ml) was also prepared from sera of the 17 patients by affinity chromatography on a DNA cellulose column. Binding to antiendothelial cell antibodies (AECA) and expression of von Willebrand factor (VWF) antigen by cultured human umbilical vein endothelial cells (HUVECs) were studied by flow cytometry.

RESULTS

The percentage of HUVECs binding to AECA or expressing VWF was greater for cells incubated with IgG from patients with SLE than for cells incubated with control IgG, though values did not reach statistical significance; nevertheless, HUVECs incubated with IgG from patients expressed a greater mean fluorescence intensity with AECA (p = 0.0001) and greater VWF expression (p = 0.019). Both the fluorescence intensity and percentage of HUVECs binding to AECA or expressing VWF were significantly greater in HUVEC incubated with IgG containing anti-dsDNA than in those incubated with anti-dsDNA depleted IgG. The concentration of VWF in the supernatant was significantly increased in HUVECs incubated with IgG containing anti-dsDNA compared with control IgG or anti-dsDNA depleted IgG. Pretreatment of HUVECs with native DNA before incubation with IgG from lupus patients did not increase binding to AECA, or expression or release of VWF.

CONCLUSIONS

Our study provides in vitro evidence that antibodies to DNA have a pathogenic role in the induction of inflammatory injury of the vascular endothelium in SLE.

Lupus-derived autoantibodies with dual autoactivity: anti-DNA and anti-Fc. I. Comparison of IgG autoreactivities with single-chain Fv derivatives

Investigations into the intrinsic affinity and reactivity of autoanti-DNA active sites were initiated through the use of purified monoclonal IgG and the synthesis of single-chain Fv derivatives of murine monoclonal anti-DNA autoantibodies BV 04-01 and BV 17-45. Results showed that relative to the respective IgG hybridomas, only the BV 04-01 SCA derivative showed demonstrable reactivity with DNA. The monovalent single-chain derivative of BV 17-45 showed no reactivity with DNA in solution or solid-phase assays, even though the parental IgG had been previously described as high affinity. However, 17-45 displayed reactivity as a bivalent single-chain derivative. In addition, upon concentration, BV 17-45 IgG formed a highly stable, papain-resistant precipitate. Investigations into the nature of the precipitate revealed that BV 17-45 possessed significant, DNA-inhibitable autobinding to its own IgG molecule. BV 04-01 also possessed similar anti-self reactivity. Thus, both monoclonal autoantibodies examined in this study possessed dual binding specificity; anti-DNa and anti-self.

No evidence for an independent role of anti-heparan sulphate reactivity apart from anti-DNA in lupus nephritis

The presence of anti-heparan sulphate (HS) reactivity in serum is closely related to the occurrence of nephritis in patients with systemic lupus erythematosus (SLE). Since patients with lupus nephritis in general also have high titres of anti-DNA antibodies, we wanted to clarify the relationship between anti-HS and anti-DNA reactivity in serum. Therefore, we studied longitudinally six patients with lupus nephritis who experienced 12 exacerbations of their disease, and five SLE patients without nephritis experiencing 10 periods of non-renal disease exacerbations. In addition, we tested single serum samples of another 24 patients obtained during a renal disease exacerbation and 22 sera of patients without nephritis. The sera of all patients were tested for anti-DNA (Farr assay) and anti-HS reactivity (ELISA). We confirmed that SLE patients during renal exacerbations have a significantly higher anti-HS reactivity than patients without nephritis (P < 0.003). In addition, patients with nephritis also had higher titres of anti-DNA antibodies during renal exacerbations than during non-renal exacerbations (P < 0.01). A correlation between anti-DNA and anti-HS reactivity was observed (r = 0.40, P < 0.02), which in itself explains the correlation between nephritis and anti-HS reactivity. Comparing sera from nephritis and non-nephritis patients matched for anti-DNA titre, we found no difference in anti-HS reactivity, and therefore must conclude that the anti-HS reactivity is a direct reflection of anti-DNA reactivity.

Endothelial cell binding by human polyclonal anti-DNA antibodies: relationship to disease activity and endothelial functional alterations

Polyclonal anti-dsDNA and anti-ssDNA antibodies (PoAb) that showed significant binding to human umbilical vein endothelial cells (HUVEC) were isolated from eight patients with systemic lupus erythematosus (SLE). Anti-dsDNA PoAbs from five patients and anti-ssDNA PoAbs from seven patients demonstrated enhanced binding to HUVEC during active disease, compared with PoAbs obtained from corresponding patients during remission. Reduction of the DNA content in the PoAb preparations by DNase treatment was associated with enhanced binding to HUVEC in 20 of 32 PoAbs tested, which included 75% 'active disease' PoAbs, and with reduced binding to HUVEC in three of 32 PoAbs tested, all obtained during remission. Such altered endothelial cell binding was reversed with DNA reconstitution. Binding of the remaining nine PoAbs to HUVEC was not altered by variations in their DNA content. Induced plasma membrane expression of E-selectin, but reduced expression of vascular cell adhesion molecule-1 (VCAM-1) by HUVEC, was observed following incubation of HUVEC with 'active disease' PoAbs from three and two of the eight patients, respectively. PoAbs and serum samples from two of the eight patients during active disease induced von Willebrand factor release from HUVEC, which was not observed during remission. We conclude that anti-DNA antibodies from selected patients with SLE can bind to endothelial cells. Correlation between cellular binding and disease activity suggests that such binding of anti-DNA antibodies to endothelial cells could be of pathogenic significance. Preliminary data also suggest that the expression of adhesion molecules and haemostatic factor(s) by endothelial cells may be modified following their binding by anti-DNA antibodies.

Molecular analyses of anti-DNA antibodies induced by polyomavirus BK in BALB/c mice

In the present experiments, two groups of BALB/c mice (five individuals in each group) were hyperimmunized through four consecutive immunizations with either BK virus (Group 1) or BK dsDNA complexed with methylated BSA (Group 2). All immune sera taken after the fourth immunization from both groups reacted strongly with polyomavirus BK dsDNA as well as with calf thymus dsDNA, and all sera contained antibodies that bound in the Crithidia luciliae assay. This indicates that polyomavirus BK was able to induce antibodies with binding characteristics similar to SLE anti-DNA antibodies. To further characterize these induced anti-DNA responses, 10 monoclonal anti-DNA antibodies (four from Group 1, and six from Group 2) were generated and selected for reactivity with S1-nuclease digested CT dsDNA. Their specificity for BK and CT dsDNA molecules, as well as their light and heavy chain variable region cDNA nucleotide sequences were analysed to compare them with known SLE derived anti-DNA antibodies. All of the 10 antibodies bound strongly to BK dsDNA, while seven also bound to CT dsDNA in competitive ELISA experiments. V-region analysis revealed that the induced antibodies resembled anti-DNA antibodies characteristic for murine SLE, and all but one contained arginine in the VH CDR3 region. The arginines present in the monoclonal antibodies originated either from an RF shift from RF1-->RF3 of the D-genes or from N-sequence additions. Taken together, the data demonstrate that anti-DNA antibodies in response to hyperimmunization with polyomavirus BK have the same characteristics as of those occurring spontaneously in SLE. As virus infection/replication in vivo implies expression of immunogenic (non-self) DNA-binding proteins that may render DNA immunogenic, the present results may therefore suggest one physiological mechanism for production of SLE-related anti-DNA antibodies.

Plasma DNA as a marker of cancerous cell death. Investigations in patients suffering from lung cancer and in nude mice bearing human tumours

Plasma DNA that circulates mainly as mononucleosomes is a cell death marker. Its significance and prognostic value in cancer as compared to other tumour markers was investigated in 68 patients hospitalised for lung cancers. Prognostic values of the various studied parameters were evaluated using the Cox's model. The cellular origin of plasma DNA was further investigated in nude mice transplanted with human lung adenocarcinoma. Plasma DNA concentrations were increased in cancer patients as compared to normal subjects (P < 0.01). They were higher in patients with extended (Stage 4) disease than in patients with limited stage disease (P < 0.05). Plasma DNA concentrations, serum lactate dehydrogenase activities and neuron-specific enolase concentrations were correlated all together in small cell lung carcinoma (SCLC) and in non-SCLC. Similar relationships were found between survival and each of these three cell death/tumour markers (P < 0.02-0.005). Plasma DNA from mice bearing human tumour hybridised with both mouse and human plasma DNA, while plasma DNA from endotoxin-injected mice hybridised only with mouse plasma DNA. In conclusion, in patients suffering from lung cancer, plasma DNA as well as LDH and NSE represent cell death markers that are correlated with survival. At a time when apoptosis pathways appear to be potential targets for cancer therapy, plasma DNA is a cell death/tumour marker that should be taken into account in studying the cancerous process in human diseases.

Glomerular uptake of nucleosomes: evidence for receptor-mediated mesangial cell binding

DNA-containing immune complexes (IC) are believed to have a central causal role in the glomerulonephritis of systemic lupus erythematosus. Extracellular DNA which provides the antigenic source for these ICs circulates as oligonucleosomes (ON). The in vivo glomerular uptake of radiolabeled ON in rats, as well as its binding by cultured rat mesangial cells, was examined. The data show that the binding of ON to kidney, and specifically glomeruli, was almost fourfold greater than that of purified DNA. Uptake appeared dose-dependent and saturable, while there were no differences in hepatic or splenic uptake. Most of the nucleosomal DNA recovered from glomeruli was TCA-precipitable, and on gel electrophoresis was about 100 to 300 bp, a size sufficient to allow formation of large ICs. In vitro studies demonstrated that ON are bound by cultured mesangial cells in a dose-dependent and saturable manner, with a dissociation constant of 1.25 x 10(-10) M/liter and 750 binding sites per cell. Autoradiography of cell cultures incubated with radiolabeled ON showed deposition along the plasma membrane which was inhibited by excess unlabeled ON. The data show that binding of ON to glomeruli exceeds that of purified DNA and may be mediated by histones. ON bind to mesangial cells in a receptor-mediated fashion. The data support the hypothesis of in situ formation of DNA-containing ICs and suggest a role for the mesangial cell in lupus glomerulonephritis.

Expression of type 1 plasminogen activator inhibitor in renal tissue in murine lupus nephritis

Many renal diseases are associated with fibrin deposition in the glomeruli, a situation that reflects an abnormality in the balance between the coagulation and fibrinolytic systems. We recently demonstrated that normal mouse kidney contains very low levels of type 1 plasminogen activator inhibitor (PAI-1), a potent anti-fibrinolytic protein, but that during endotoxemia, large amounts of PAI-1 protein and mRNA are expressed in glomerular and peritubular endothelial cells. These results raise the possibility that overexpression of PAI-1 in the glomerulus may contribute to the ongoing pathology seen in renal disease. To directly investigate this possibility, we studied PAI-1 expression in MRL/lpr mice, using in situ hybridization and immunohistochemistry. Female MRL/lpr mice develop early onset lupus glomerulonephritis (GN), a disease in which fibrin deposition is detected in the glomerulus and in which anti-coagulation therapy improves the prognosis. We detected very low levels of PAI-1 mRNA and antigen in the smooth muscle cells of renal vessels and in the renal papilla of 16 control mice. In contrast, PAI-1 was expressed in relatively high levels throughout the kidneys of 33 out of 34 diseased mice, both within the glomerulus and also in tubules and vessels. Moreover, the level of PAI-1 in the tissues seemed to correlate with the severity of the disease. PAI-1 expression was localized to endothelial cells, parietal epithelial cells, tubular epithelial cells and infiltrating mononuclear cells in the tubulointerstitium. None of these cells express detectable levels of PAI-1 in the normal kidney. The inappropriate expression of PAI-1 in the kidneys of mice with lupus GN suggests that this important inhibitor of fibrinolysis may play a role in the pathogenesis of this disease process.

Effect of histone and histone-RNA complexes on the disease process of murine systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterised by the production of a variety of autoantibodies against cell surface, nuclear and cytoplasmic antigens. The antigen or antigens responsible for the induction of this disease is/are unknown. We have analysed the antigenicity and pathogenicity of free histones and histones complexed with RNA in Balb/c, B10 Br, C57BL/6 and MRL-lpr/lpr mice by giving 1 microgram and 25 micrograms of each antigen intraperitoneally in complete and incomplete Freund's adjuvant. The same number of control animals were injected with either adjuvant or PBS. In the initial experiment we gave three doses of antigen at three weekly intervals. B10 Brown and C57BL/6 mice had no response to the antigens. Balb/c mice developed a mild transient antibody response against H1 histone, branched peptide of ubiquitinated H2A (peptide T4) and also against ssDNA. However in repeated experiments when the histone-RNA complex was injected into young MRL-lpr/lpr animals at two weekly intervals, a significantly increased antibody response was detected against H1, peptide T4 and some histone peptide residues (204-218 of H1, 1-20 and 65-85 of H2A, 1-25 of H2B, 1-21 of H3 and 1-29 of H4) compared to the control groups. Moreover, this group also showed elevated serum anti-DNA antibody levels and early impairment of renal function assessed by the urine protein levels. These experiments have demonstrated that there is a genetic variation in antibody responses against histones and histone-RNA complexes and that histone-RNA complexes exaggerate the disease in young MRL-lpr/lpr mice by inducing antibodies to basic regions of histones and other autoantigens.

A new ELISA for the detection of anti-heparan sulfate reactivity, using photobiotinylated antigen

Autoantibodies reacting with a great variety of autoantigens are characteristic for the autoimmune disease systemic lupus erythematosus (SLE). Although reactivity with heparan sulfate (HS) in sera of patients with SLE is found in association with the occurrence of nephritis, the aetiological significance of this association is not clear. The assay which is generally used to measure anti-HS reactivity is subject to false-positive results, as a consequence of the binding of negatively charged moieties within immune complexes to the precoat employed (protamine sulfate). Therefore, we have developed a new ELISA in which photobiotinylated HS is efficiently and reproducibly bound to streptavidin-coated wells. We compared the new ELISA with the classical anti-HS ELISA by testing culture supernatants of 20 murine monoclonal antibodies (mAb) to DNA (containing free anti-DNA and anti-DNA/nucleosome immune complexes) and preparations of these mAb (containing only free anti-DNA), purified under dissociating conditions. In the classical anti-HS ELISA, 14 out of 20 of the culture supernatants reacted positively with HS; after purification no reactivity remained. The discrepancy must be due to anti-DNA/nucleosome immune complexes present in the culture supernatants. In the new ELISA only four out of 20 culture supernatants and one of the purified preparations reacted with HS. This latter reactivity is probably not specific, since this mAb also reacted with streptavidin alone. To find out whether there is a correlation between the occurrence of nephritis and anti-HS reactivity, measured in this new anti-HS ELISA, we tested sera of patients with a renal- or non-renal exacerbation of SLE in the newly developed anti-HS ELISA. We observed a correlation between anti-HS reactivity and nephritis.

Fas ligation triggers apoptosis in macrophages but not endothelial cells

The reticuloendothelial system includes macrophages and endothelial cells. These cells are produced and destroyed in vivo with a precision that implies the existence of homeostatic mechanisms. The stimuli for endothelial cell proliferation and monocyte production are becoming well characterized. However, the mechanisms involved in eliminating these cells are poorly understood. One mechanism involved in cellular elimination is apoptosis, which can be triggered in some cells by ligation of the Fas molecule. In this report we have investigated whether macrophages and endothelial cells express the Fas molecule, and whether Fas transmits an apoptosis-inducing signal in these cells. We demonstrate that macrophages express Fas and readily undergo apoptosis when cultured with anti-Fas. In contrast, while endothelial cells can express the Fas molecule, Fas ligation is insufficient to induce apoptosis. These results suggest differential regulation of Fas function among cells of the reticuloendothelial system, and imply different mechanisms of homeostasis.

Urinary DNA as an indicator of nephrotoxicity caused by endotoxin and gentamicin in mice

Extracellular DNA is a non-specific marker of cell death. Urinary DNA, as an indicator of nephrotoxicity, was investigated in endotoxin/gentamicin-injected mice. In mice injected both with endotoxin (15 mg/kg) and gentamicin (80 mg/kg), urinary DNA concentration was markedly increased for several days; in contrast, there was at most a slight and transient excretion of DNA in mice receiving gentamicin or endotoxin alone. Plasma DNA concentrations increased for 24-48 h in endotoxin-injected mice, then decreased rapidly. Mice injected with gentamicin and endotoxin showed widespread and severe kidney lesions with tubular cell necrosis and intraluminal casts while mice receiving gentamicin or endotoxin alone showed at most few and mild lesions. In mice receiving lower doses of endotoxin (5-10 mg/kg) and 80 mg/kg gentamicin, urinary DNA peaked at 72-96 h, at a time when plasma DNA had returned to normal concentrations. Maximal urinary DNA concentrations depended upon endotoxin dose. In conclusion, urinary DNA is a marker of definite cell death occurring in the urinary tract and could represent a new indicator of nephrotoxicity in clinical and experimental situations.

In vitro inhibition of natural-killer-mediated lysis by chromatin fragments

A qualitative impairment of natural killer (NK) function and the presence of circulating DNA have been independently reported in clinical situations such as cancer and lupus. The existence of receptors for chromatin fragments at the leukocyte membrane raised the question of the relation between the presence of chromatin fragments in the extracellular medium and the impairment of NK function. The present study shows that plasmas from patients with metastatic cancer and with pathological DNA concentrations inhibited significantly the NK activity of normal lymphocytes as compared to cancer plasmas with DNA concentrations in the normal range. In vitro, it was demonstrated that chromatin fragments inhibited the NK-mediated cytotoxicity in a dose-dependent manner. Inhibitory concentrations of nucleosomes (2.5-10 micrograms/ml) were lower than those of DNA and histones alone (100 micrograms/ml). Inhibitory effects of nucleosomes, DNA and histones differed also according to the effector population used: nucleosomes were effective whatever the CD56+ cell enrichment of the effector population, while DNA inhibition needed T cells, and histone inhibition probably resulted from a subtoxic effect, prevented by the presence of adherent cells. Finally we found that nucleosomes could inhibit the NK function only when they were present in the extracellular medium. Taken together, these data suggest that the persistence of nucleosomal DNA at sites of cell death or in the blood might be responsible, at least partly, for the NK activity impairment observed in pathological circumstances characterized by a high rate of cell death phenomena such as cancer.

Conjugates or dsDNA linked to human gammaglobulin inhibit anti-dsDNA antibodies in vitro

Previous studies have shown that both nucleosides and oligonucleotides linked to isologous gammaglobulin suppress anti-nucleic acid antibody production both in vivo and in vitro. The aim of this study was to determine whether one can make a DNA-human gammaglobulin (HGG) conjugate which can inhibit anti-double stranded DNA (dsDNA) antibodies obtained from a heterogeneous population of systemic lupus erythematosus (SLE) sera. To do so, we constructed conjugates of sonicated dsDNA fragments of 100-400 base pairs covalently linked to HGG with varying degrees of substitution of DNA:HGG. An ELISA inhibition assay was used to determine which conjugate best inhibits the binding of anti-dsDNA antibodies. Conjugate 2, prepared with monomeric HGG (150 kD) with a high degree of substitution (3.72 DNA:HGG) inhibited the binding of anti-dsDNA antibodies from 27 of 31 SLE sera. In addition, this conjugate inhibited the spontaneous formation of anti-dsDNA in vitro by cultured lymphoid cells from selected SLE patients. Together, this data suggests that a 'generic' tolerogen may provide an antigen specific therapy for SLE.

Histone mediates glomerular deposition of small size DNA anti-DNA complex

Histone can mediate the binding of free DNA to the glomerular capillary wall. We tested whether histone could mediate the deposition of preformed DNA-anti-DNA immune complex (IC). IC were generated using monoclonal anti-DNA Ab and excess of small size 125I-DNA; after further digestion with DNase the IC, containing 5 micrograms DNA (now 20 to 60 bp), was injected into the left kidney of rats. When given alone, only about 0.2% of the IC bound in glomeruli. Prior injection of 200 micrograms of core histones (H2A,H2B,H3,H4) resulted in high glomerular binding of the IC; 18.1% of the injected dose (measured as 125I-DNA) was bound at 15 minutes. Mouse immunoglobulin, representing the IC, could be seen in a capillary pattern. C3 was also present in a similar pattern, showing that complement had been activated. Discrete electron-dense deposits were seen in a subendothelial and subepithelial localization at 15 minutes. Although about 1 microgram of DNA was deposited in the glomeruli, it could not be detected by indirect immunofluorescence or intercalating dyes. These studies provide direct evidence that histones can mediate the binding of particular circulating DNA-anti-DNA immune complexes to the glomerular capillary wall in vivo. If small size DNA fragments (< 100 bp) are involved in lupus nephritis, our results provide a possible explanation for the frequent failure to detect DNA deposits in renal biopsies from SLE patients.

Preferential adsorption of cationic anti-DNA antibodies with immobilized polyanionic compounds, dextran sulfate

It has been shown that cationic anti-DNA antibodies have nephritogenic potential in murine models of lupus nephritis. More recently, we have reported that there is a close relationship between the presence of circulating cationic anti-DNA antibodies and the development of lupus nephritis in humans, and that the cationic anti-DNA antibodies bind to heparan sulfate, a major glycosaminoglycan in glomerular basement membrane, much better than neutral anti-DNA antibodies. This suggests that cationic anti-DNA antibodies of the IgG class may be responsible for development of nephritis in vivo in patients with systemic lupus erythematosus. In this study, we first studied reactivity of anti-DNA antibodies with a panel of glycosaminoglycans in vitro using ELISA methods, and found that anti-DNA antibodies cross-react with dextran sulfate, hyaluronic acid and chrondroitin sulfate. The reactivity and selectivity of dextran sulfate with anti-DNA antibodies was confirmed by in vitro immunoadsorption of the patient's sera with dextran sulfate-fixed column; incubation of auto-antibody-positive sera with dextran sulfate cellulose column removed anti-DNA, but not anti-RNP, anti-Sm, anti-SSA and anti-SSB antibodies from the sera in vitro. Of note is that dextran sulfate cellulose column absorbed exclusively, if not all, cationic anti-DNA antibodies in their sera. Nonspecific binding of total immunoglobulins as well as total proteins to the column was marginal. It has been suggested that cationic anti-DNA antibodies in sera of patients with refractory lupus nephritis could be efficiently removed by apheresis using dextran sulfate column.

Higher anti-heparan sulphate reactivity during systemic lupus erythematosus (SLE) disease exacerbations with renal manifestations; a long term prospective analysis

Cross-reactive antibodies against heparan sulphate (HS) have been suggested to play a role in initiating renal disease in SLE. Recently, we found that HS-reactivity is mediated by anti-DNA antibodies complexed with DNA and histones. To evaluate the clinical significance of anti-HS reactivity, we studied prospectively a cohort of 72 consecutive SLE patients, of whom 22 experienced 40 exacerbations. In 20 of these exacerbations renal symptoms were present. In these 20 exacerbations significantly higher anti-DNA (median 1:160) and anti-HS (median 1:30) titres were detected compared with exacerbations without renal manifestations (median 1:60 for anti-DNA and negative for anti-HS). There were no correlations with other symptoms of SLE. Anti-HS titres showed a significant correlation with anti-DNA antibody titres (rs = 0.57, P < 0.05). Anti-HS without anti-DNA reactivity was never detected. Some SLE patients showed a high anti-DNA titre without anti-HS reactivity, suggesting that not all anti-DNA antibodies are able to bind to histone/DNA complexes and thus to exhibit anti-HS reactivity. Our findings indicate that anti-HS reactivity is correlated with renal disease in SLE.

Specific increases in urinary excretion of anti-DNA antibodies in lupus mice induced by lysozyme administration: further evidence for DNA-anti-DNA immune complexes in the pathogenesis of nephritis

We previously reported that lysozyme electrostatically inhibits the fibronectin-mediated DNA binding to the glomerular basement membrane (GBM) and reduces in situ DNA-anti-DNA complex formation in the GBM in NZB/W F1 mice [1]. In this study, we further noticed significant increases in urinary excretion of anti-DNA antibodies and immune complexes (IC) in lysozyme-treated NZB/W F1 mice. Their clearance ratios of IgG anti-DNA antibody to whole IgG were markedly high compared with those of saline-treated animals. A large number of IgG and C3 positive granules were observed in the tubular cells of NZB/W F1 mice treated with lysozyme. On the contrary, nil or only small amounts of anti-DNA antibodies were detected in the urine of NZB/W F1 mice without lysozyme administration despite a large amount of proteinuria, suggesting entrapment of the antibodies in lupus glomeruli. Lysozyme neither inhibited the binding of anti-DNA antibodies to DNA or heparan sulphate nor did it displace anti-DNA antibodies and IC from the kidney homogenates of lupus mice. It thus appears that the inhibition of DNA binding to the GBM due to lysozyme reduced the entrapment of anti-DNA antibodies in the GBM, resulting in urinary excretion of the antibodies.