Binding of nucleosomes to a cell surface receptor: redistribution and endocytosis in the presence of lupus antibodies

DNA-Binding Proteins and Passenger Proteins in Plasma DNA-Protein Complexes: Imprint of Parental Cells or Key Mediators of Carcinogenesis Processes?

Knowledge of the composition of proteins that interact with plasma DNA will provide a better understanding of the homeostasis of circulating nucleic acids and the various modes of interaction with target cells, which may be useful in the development of gene targeted therapy approaches. The goal of the present study is to shed light on the composition and architecture of histone-containing nucleoprotein complexes (NPCs) from the blood plasma of healthy females (HFs) and breast cancer patients (BCPs) and to explore the relationship of proteins with crucial steps of tumor progression: epithelial-mesenchymal transition (EMT), cell proliferation, invasion, cell migration, stimulation of angiogenesis, and immune response. MALDI-TOF mass spectrometric analysis of NPCs isolated from blood samples using affine chromatography was performed. Bioinformatics analysis showed that the shares of DNA-binding proteins in the compositions of NPCs in normal and cancer patients are comparable and amount to 40% and 33%, respectively; in total, we identified 38 types of DNA-binding motifs. Functional enrichment analysis using FunRich 3.13 showed that, in BCP blood, the share of DNA-binding proteins involved in nucleic acid metabolism increased, while the proportion of proteins involved in intercellular communication and signal transduction decreased. The representation of NPC passenger proteins in breast cancer also changes: the proportion of proteins involved in transport increases and the share of proteins involved in energy biological pathways decreases. Moreover, in the HF blood, proteins involved in the processes of apoptosis were more represented in the composition of NPCs and in the BCP blood-in the processes of active secretion. For the first time, bioinformatics approaches were used to visualize the architecture of circulating NPCs in the blood and to show that breast cancer has an increased representation of passenger proteins involved in EMT, cell proliferation, invasion, cell migration, and immune response. Using breast cancer protein data from the Human Protein Atlas (HPA) and DEPC, we found that 86% of NPC proteins in the blood of BCPs were not previously annotated in these databases. The obtained data may indirectly indicate directed protein sorting in NPCs, which, along with extracellular vesicles, can not only be diagnostically significant molecules for liquid biopsy, but can also carry out the directed transfer of genetic material from donor cells to recipient cells.

Extracellular histones as damage-associated molecular patterns in neuroinflammatory responses

The four core histones H2A, H2B, H3, H4, and the linker histone H1 primarily bind DNA and regulate gene expression within the nucleus. Evidence collected mainly from the peripheral tissues illustrates that histones can be released into the extracellular space by activated or damaged cells. In this article, we first summarize the innate immune-modulatory properties of extracellular histones and histone-containing complexes, such as nucleosomes, and neutrophil extracellular traps (NETs), described in peripheral tissues. There, histones act as damage-associated molecular patterns (DAMPs), which are a class of endogenous molecules that trigger immune responses by interacting directly with the cellular membranes and activating pattern recognition receptors (PRRs), such as toll-like receptors (TLR) 2, 4, 9 and the receptor for advanced glycation end-products (RAGE). We then focus on the available evidence implicating extracellular histones as DAMPs of the central nervous system (CNS). It is becoming evident that histones are present in the brain parenchyma after crossing the blood-brain barrier (BBB) or being released by several types of brain cells, including neurons, microglia, and astrocytes. However, studies on the DAMP-like effects of histones on CNS cells are limited. For example, TLR4 is the only known molecular target of CNS extracellular histones and their interactions with other PRRs expressed by brain cells have not been observed. Nevertheless, extracellular histones are implicated in the pathogenesis of a variety of neurological disorders characterized by sterile neuroinflammation; therefore, detailed studies on the role these proteins and their complexes play in these pathologies could identify novel therapeutic targets.

The Influence of Proteins on Fate and Biological Role of Circulating DNA

Circulating DNA has already proven itself as a valuable tool in translational medicine. However, one of the overlooked areas of circulating DNA research is its association with different proteins, despite considerable evidence that this association might impact DNA's fate in circulation and its biological role. In this review, we attempt to shed light on current ideas about circulating DNA origins and forms of circulation, known biological effects, and the clinical potential of circulating tumor deoxyribonucleoprotein complexes.

Role of Cell-Free DNA and Deoxyribonucleases in Tumor Progression

Many studies have reported an increase in the level of circulating cell-free DNA (cfDNA) in the blood of patients with cancer. cfDNA mainly comes from tumor cells and, therefore, carries features of its genomic profile. Moreover, tumor-derived cfDNA can act like oncoviruses, entering the cells of vulnerable organs, transforming them and forming metastatic nodes. Another source of cfDNA is immune cells, including neutrophils that generate neutrophil extracellular traps (NETs). Despite the potential eliminative effect of NETs on tumors, in some cases, their excessive generation provokes tumor growth as well as invasion. Considering both possible pathological contributions of cfDNA, as an agent of oncotransformation and the main component of NETs, the study of deoxyribonucleases (DNases) as anticancer and antimetastatic agents is important and promising. This review considers the pathological role of cfDNA in cancer development and the role of DNases as agents to prevent and/or prohibit tumor progression and the development of metastases.

Cellular uptake of extracellular nucleosomes induces innate immune responses by binding and activating cGMP-AMP synthase (cGAS)

The nucleosome is the basic structural repeating unit of chromatin. DNA damage and cell apoptosis release nucleosomes into the blood circulatory system, and increased levels of circulating nucleosomes have been observed to be related to inflammation and autoimmune diseases. However, how circulating nucleosomes trigger immune responses has not been fully elucidated. cGAS (cGMP-AMP synthase) is a recently discovered pattern recognition receptor that senses cytoplasmic double-stranded DNA (dsDNA). In this study, we employed in vitro reconstituted nucleosomes to examine whether extracellular nucleosomes can gain access to the cytoplasm of mammalian cells to induce immune responses by activating cGAS. We showed that nucleosomes can be taken up by various mammalian cells. Additionally, we found that in vitro reconstituted mononucleosomes and oligonucleosomes can be recognized by cGAS. Compared to dsDNA, nucleosomes exhibit higher binding affinities to cGAS but considerably lower potency in cGAS activation. Incubation of monocytic cells with reconstituted nucleosomes leads to limited production of type I interferons and proinflammatory cytokines via a cGAS-dependent mechanism. This proof-of-concept study reveals the cGAS-dependent immunogenicity of nucleosomes and highlights the potential roles of circulating nucleosomes in autoimmune diseases, inflammation, and antitumour immunity.

Monoclonal anti-dsDNA antibody 2C10 escorts DNA to intracellular DNA sensors in normal mononuclear cells and stimulates secretion of multiple cytokines implicated in lupus pathogenesis

There have been many studies on the mechanisms of internalization of DNA–anti‐DNA immune complexes by cells, including the one used for rheumatoid factor‐expressing mouse B cells. In parallel, studies on the role of intracellular DNA sensors in the pathogenesis of systemic lupus erythematosus (SLE) have been conducted, including the one using a mouse model lacking one of the sensors. These and other data have established a framework for understanding the pathogenic role of anti‐DNA antibodies, but studies on normal cells are limited. Here, we used the monoclonal anti‐dsDNA antibody 2C10, 2‐kbp dsDNA and healthy human peripheral blood mononuclear cells (PBMCs) to test whether and how 2C10 and/or DNA cause pathology in normal cells. We found that on culture with PBMCs, 2C10 preferentially entered monocytes and that DNA enhanced this internalization. In contrast, DNA alone was not significantly internalized by monocytes, but 2C10 facilitated its internalization. This was suppressed by cytochalasin D, but not by methyl‐β‐cyclodextrin, chloroquine or an Fc blocker, suggesting the involvement of macropinocytosis in this process. Internalization of 2C10 and DNA together resulted in production of interferon (IFN)‐α, IFN‐γ, tumor necrosis factor (TNF)‐α, monocyte chemoattractant protein‐1 (MCP‐1), interleukin (IL)‐1β, IL‐6, IL‐10 and IL‐33 by PBMCs. Cytokine production was suppressed by chloroquine and shikonin, but not by RU.521, suggesting dependence on activation of the Toll‐like receptor (TLR)‐9 and absent in melanoma 2 (AIM‐2) pathways. These results established a simple model to demonstrate that anti‐DNA antibodies can cause dysregulation of cytokine network mimicking systemic lupus erythematosus in culture of normal PBMCs, and emphasize again the importance of maintaining anti‐DNA antibodies at low levels by treatment.

Cell-surface-bound circulating DNA in the blood: Biology and clinical application

Cell-surface-bound extracellular DNA (csbDNA) is present on the outer membrane of blood cells, including both red blood cells and leukocytes. Although less well characterized than cell-free DNA (cfDNA) in plasma and serum, leukocyte and red blood cell csbDNA form a considerable fraction of the blood extracellular nucleic acids pool, with typically at least comparable amount of DNA occurring bound to the outer surface of cells as compared with circulating free DNA in plasma. The cellular origin of csbDNA is not clear; however, as with cfDNA, in patients with cancer a proportion is derived from the tumor, thus making it potentially a useful source of DNA for cancer diagnosis, prognosis, and monitoring. © 2019 IUBMB Life, 71(9):1201-1210, 2019.

Anti-β2 -glycoprotein I antibody with DNA binding activity enters living monocytes via cell surface DNA and induces tissue factor expression

Autoantibodies characteristic for anti‐phospholipid syndrome (APS) and systemic lupus erythematosus (SLE) are anti‐β₂‐glycoprotein I (β₂GPI) antibodies and anti‐DNA antibodies, respectively, and almost half of APS cases occur in SLE. Anti‐β₂GPI antibodies are recognized to play a pivotal role in inducing a prothrombotic state, but the precise mechanism has not been fully elucidated. In a widely accepted view, binding of anti‐β₂GPI antibodies to cell surface β₂GPI in monocytes and endothelial cells triggers the Toll‐like receptor 4‐myeloid differentiation primary response 88 (TLR)‐4‐MyD88) signaling pathway which leads to activation of p38 mitogen‐activated protein kinase (MAPK), mitogen‐activated protein kinase kinase 1/extracellular signal‐regulated kinases (MEK‐1/ERK) and/or nuclear factor kappa B (NF‐κB) and expression of tissue factor (TF). However, resting cells do not express substantial amounts of TLR‐4. Previously, we generated a mouse monoclonal anti‐β₂GPI antibody WB‐6 and showed that it induced a prothrombotic state – including TF expression on circulating monocytes – in normal mice. In the current study, we aimed to clarify the mechanism of interaction between WB‐6 and resting monocytes, and found that WB‐6 exhibits binding activity to DNA and enters living monocytes or a monocytic cell line and, to a lesser extent, vascular endothelial cells. Treatment of the cells with DNase I reduced the internalization, suggesting the involvement of cell surface DNA in this phenomenon. Monocytes harboring internalized WB‐6 expressed TF and tumor necrosis factor (TNF)‐α which, in turn, stimulated endothelial cells to express intercellular adhesion molecule 1 (ICAM‐I) and vascular cell adhesion molecule 1 (VCAM‐I). These results suggest the possibility that a subset of anti‐β₂GPI antibodies with dual reactivity to DNA possesses ability to stimulate DNA sensors in the cytoplasm, in addition to the cell surface receptor‐mediated pathways, leading to produce proinflammatory and prothrombotic states.

In vivo histone H1 migration from necrotic to viable tissue

Necrosis is induced by ischemic conditions within the core of many solid tumors. Using fluorescent fusion proteins, we provide in vivo evidence of histone trafficking among cancer cells in implanted tumors. In particular, the most abundant H1 isoform (H1.2) was found to be transported from necrotic tumor cells into surrounding viable cells where histones are selectively taken up by energy-dependent endocytosis. We propose that intercellular histone trafficking could function as a target for drug delivery. This concept was validated using an anti-histone antibody that was co-internalized with histones from dead cells into viable ones surrounding the necrotic regions of a tumor, where some of the most chemoresistant cells reside. These findings demonstrate that cellular translocation of conjugated drugs using anti-histone antibodies is a promising strategy for targeted drug delivery to chemoresistant tumors.

Extracellular histones, cell-free DNA, or nucleosomes: differences in immunostimulation

In inflammation, extensive cell death may occur, which results in the release of chromatin components into the extracellular environment. Individually, the purified chromatin components double stranded (ds)DNA and histones have been demonstrated, both in vitro and in vivo, to display various immunostimulatory effects, for example, histones induce cytotoxicity and proinflammatory signaling through toll-like receptor (TLR)2 and 4, while DNA induces signaling through TLR9 and intracellular nucleic acid sensing mechanisms. However, DNA and histones are organized in nucleosomes in the nucleus, and evidence suggests that nucleosomes are released as such in inflammation. The cytotoxicity and proinflammatory signaling induced by nucleosomes have not been studied as extensively as the separate effects brought about by histones and dsDNA, and there appear to be some marked differences. Remarkably, little distinction between the different forms in which histones circulate has been made throughout literature. This is partly due to the limitations of existing techniques to differentiate between histones in their free or DNA-bound form. Here we review the current understanding of immunostimulation induced by extracellular histones, dsDNA and nucleosomes, and discuss the importance of techniques that in their detection differentiate between these different chromatin components.

Testing for anti-nucleosome antibodies in daily practice: a monocentric evaluation in 1696 patients

The objective was to report our experience of the detection of anti-nucleosome (anti-Nuc) antibodies (Ab) in a large series of consecutive patients, and to compare these results with those of anti-nuclear and anti-dsDNA Ab. In total, 1696 consecutive patients with suspected or confirmed autoimmune disease were tested over a two-year period. The biological investigation included detection of anti-nuclear, anti-dsDNA and anti-Nuc Ab. Among 1696 sera, 382 (23%) were negative for all Ab tested (anti-nuclear, anti-dsDNA and anti-Nuc) and 1314 (77%) were positive for at least one Ab. Anti-Nuc Ab were positive in 350/1314 patients. In this group, 249/350 (71%) also had positive anti-nuclear and anti-dsDNA, 97/350 (28%) had only positive anti-nuclear Ab without anti-dsDNA Ab and 4/350 (1%) had both anti-dsDNA and anti-Nuc Ab without anti-nuclear Ab. No patient had ‘isolated’ anti-Nuc Ab. Clinical data were available for 307/350 anti-Nuc positive patients. Systemic lupus erythematosus (SLE) was diagnosed in 240/307 (78%) patients, including 43 SLE patients with negative anti-dsDNA Ab. In conclusion, this study extends the relevance of anti-Nuc Ab to routine use for the diagnosis of connective tissue diseases, mainly anti-dsDNA Ab negative SLE.

[Protein Identification of Blood Nucleoprotein Complexes]

Circulating nucleoprotein complexes were isolated-from blood plasma by affinity chromatography using immobilized polyclonal anti-histone antibodies. It was found, that the main part of DNA from histone-contained nucleoprotein complexes have size 170-180 b.p., in blood of breast cancer patients DNA with size 170-180 b.p. and DNA more then 6 k.b.p. are presented in equal quantity. Proteins from circulating nucleoprotein complexes were identified using MALDI-TOF mass-spectrometry. It was shown that nucleoprotein complexes from blood of breast cancer patients contain tumor-specific proteins, such as LDOC1L, ADP/ATP translocase 3 and Lamellipodin. These data indicate, that a part of circulating extracellular DNA have tumor origin.

DNA-histone complexes as ligands amplify cell penetration and nuclear targeting of anti-DNA antibodies via energy-independent mechanisms

We have generated three monoclonal cell-penetrating antibodies (CPAbs) from a non-immunized lupus-prone (NZB × NZW)F1 mouse that exhibited high anti-DNA serum titres. These CPAbs are polyreactive because they bind to DNA and other cellular components, and localize mainly in the nucleus of HeLa cells, albeit with a distinct nuclear labelling profile. Herein, we have examined whether DNA-histone complexes (DHC) binding to CPAbs, before cell entry, could modify the cell penetration of CPAbs or their nuclear staining properties. By applying confocal microscopy and image analysis, we found that extracellular binding of purified CPAbs to DHC significantly enhanced their subsequent cell-entry, both in terms of percentages of positively labelled cells and fluorescence intensity (internalized CPAb amount), whereas there was a variable effect on their nuclear staining profile. Internalization of CPAbs, either alone or bound to DHC, remained unaltered after the addition of endocytosis-specific inhibitors at 37° or assay performance at 4°, suggesting the involvement of energy-independent mechanisms in the internalization process. These findings assign to CPAbs a more complex pathogenetic role in systemic lupus erythematosus where both CPAbs and nuclear components are abundant.

Immunological evidence and regulatory potential for cell-penetrating antibodies in intravenous immunoglobulin

Anti-DNA cell-penetrating autoantibodies have been extensively studied in autoimmune but not in normal sera. We investigated herein the presence and properties of cell-penetrating antibodies (CPAbs) in intravenous immunoglobulin (IVIg), a blood product of pooled normal human IgG. IVIg cell penetration was observed into various cell lines, as well as cells from several organs of mice injected intravenously with IVIg therapeutic dose. In all cell types examined in vitro and in vivo, intracellular IgG localized in the cytoplasm, in contrast to the nuclear accumulation of disease-related CPAbs. IVIg was found to rapidly enter cells via an energy-independent mode. The CPAb-fraction was isolated and found to be polyreactive to nuclear and cytoplasmic components; although it corresponded to ~2% of IVIg, it accounted for its inhibitory effect on splenocyte activation. Investigation of IVIg cell penetration capacity provides insight into its mechanisms of action and may account for some of its beneficial effects in numerous diseases.

Generation of blood circulating DNA: the sources, peculiarities of circulation and structure

Extracellular nucleic acids (exNA) were described in blood of both healthy and illness people as early as in 1948, but staied overlooked until middle 60-th. Starting from the beginning of new millennium and mainly in the last 5 years exNA are intensively studied. Main attention is directed to investigation of exNA as the source of diagnostic material whereas the mechanisms of their generation, as well as mechanisms to providing long-term circulation of exNA in the bloodstream are not established unambiguously. According to some authors, the main source of circulating nucleic acids in blood are the processes of apoptosis and necrosis, while others refer to the possible nucleic acid secretion by healthy and tumor cells. Circulating DNA were found to be stable in the blood for a long time, escaping from the action of DNA hydrolyzing enzymes and are apparently packed in different supramolecular complexes. This review presents the opinions of various authors and evidence in favor of all the theories describingappearance of extracellular DNA, the features of the circulation and structure of the extracellular DNA and factors affecting the time of DNA circulation in blood

Antinuclear antibodies with nucleosome-restricted specificity for targeted delivery of chemotherapeutic agents

Circulating antinuclear autoantibodies (ANAs) are well known to accompany various pathological conditions and can be artificially induced by immunization. Research and clinical data permit us to hypothesize a definite connection between cancer and ANAs. Based on the available data, my group's research suggested that exogenous ANAs may be used as anticancer therapeutics. Among these ANAs, nucleosome-specific ANAs may be particularly useful. Advances in cancer immunotherapy with monoclonal antibodies re-emphasized the role of humoral immunity in neoplasia control. The development of a universal antibody targeting diverse cancers is of clear importance. We showed that certain natural ANAs recognize the surface of numerous tumor cells but not normal cells via cell surface-bound nucleosomes originating from the apoptotically dying neighboring tumor cells, mediate antibody-dependent cellular cytotoxicity of tumor cells in vitro and inhibit the development of murine tumor in syngeneic mice. A single monoclonal antinuclear nucleosome-specific autoantibody, mAb 2C5, specifically recognizes multiple unrelated human tumor cell lines and accumulates at a high tumor-to-normal cell ratio in various human tumors in nude mice. Immunotherapy with mAb 2C5 resulted in significant suppression of the growth of several human tumors. In addition, mAb 2C5, when used in subtherapeutic quantities, can serve as a highly efficient specific ligand to target various drug- or diagnostic agent-loaded pharmaceutical nanocarriers, such as liposomes and polymeric micelles, to various tumors. Here, the data (accumulated predominantly in our laboratory over several years) on mAb 2C5-mediated tumor targeting of chemotherapeutic agents is reviewed.

Nucleosome-induced neutrophil activation occurs independently of TLR9 and endosomal acidification: implications for systemic lupus erythematosus

The nucleosome is a major autoantigen known to activate PMN in systemic lupus erythematosus (SLE). TLR9 recognizes bacterial and even mammalian DNA under certain circumstances. Nevertheless, the role of TLR9 in SLE development is still unclear. Since nucleosomes are composed of DNA, we investigated whether TLR9 is required for nucleosome-induced PMN activation. Isolated neutrophils were cultured with nucleosomes, plasma from lupus patients and other stimuli in the presence/absence of various inhibitors. Cells were analyzed by flow cytometry, ELISA and confocal microscopy. We found that nucleosomes circulating in lupus plasma induce the secretion of pro-inflammatory cytokines by PMN. Nucleosomes activate human PMN independently of unmethylated CpG sequences in nucleosomal DNA, leading to IL-8/IL-6/TNF secretion and CD11b up-regulation. Nucleosomes accumulate in the cytoplasm of PMN upon endocytosis, induce TLR9 up-regulation and act synergistically with TLR9 ligands. Nucleosome-induced activation was not inhibited by polymyxin B (PB), chloroquine (CQ), ammonium chloride (AC) or a TLR9 antagonist. Moreover, both PMN isolated from WT and TLR9-KO mice were activated by nucleosomes, as detected by MIP-2 secretion and CD11b up-regulation. Activation occurred therefore independently of endotoxins, endosomal acidification, TLR9 and CpG motifs. TLR9 may thus be differently required in the triggering of nucleosome-induced innate immunity and anti-nucleosome B-cell autoimmunity.

Gadolinium-Loaded Polychelating Polymer-Containing Cancer Cell-Specific Immunoliposomes

Liposome loading with Gd via the membrane-incorporated polychelating amphiphilic polymers (PAPs) significantly increases the Gd content and relaxivity (T1 parameter) of PEGylated liposomes, which can be used as contrast agents for magnetic resonance imaging (MRI). Here, we demonstrate that such Gd-containing liposomes can be additionally modified with the monoclonal anticancer antibody 2C5 (mAb 2C5) possessing the nucleosome(NS)-restricted specificity via the PEG spacer. Liposome-bound antibody preserves its specific activity (ELISA) and such Gd-loaded PEGylated 2C5-immunoliposomes specifically recognize various cancer cells in vitro and target an increased amount of Gd to their surface compared to antibody-free Gd-liposomes or Gd-liposomes modified with tumor nonspecific antibody. Gd-loaded cancer cell-targeted immunoliposomes may represent promising agents for enhanced tumor MRI.

Enhanced tumor MR imaging with gadolinium-loaded polychelating polymer-containing tumor-targeted liposomes

PURPOSE

To significantly enhance tumor MR imaging by using a contrast agent combining three components -- a long-circulating liposome, liposomal membrane-incorporated polychelating amphiphilic polymer heavily loaded with gadolinium, and cancer-specific monoclonal antibody 2C5 attached to the liposome surface.

MATERIALS AND METHODS

Tumor-bearing animals were imaged prior and 4, 24, and 48 hours after i.v. injection of 2C5-modified and unmodified Gd-PAP-containing PEGylated liposomes. The faster and more specific accumulation of the novel contrast nanoparticles in tumors was also confirmed by 3D angiograms and by direct visualization of Gd-immunoliposomes in tumor sections by confocal microscopy.

RESULTS

2C5-modified Gd-PAP-containing PEGylated liposomes allowed for fast and specific tumor imaging as early as 4 hours postinjection. T1 inversion recovery maps demonstrated a significant increase in tumor-associated R1 in animals injected with antibody-modified Gd-loaded liposomes 4 hours postinjection, followed by a gradual decrease consistent with clearance of the agent from the tumor region. In control animals injected with antibody-free liposomes the corresponding R1 values at all investigated timepoints were significantly smaller.

CONCLUSION

The results support the feasibility of using such multifunctional nanoparticular liposome-based agents simultaneously providing prolonged circulation, heavy Gd load, and specific cancer cell recognition as a superior contrast for MR tumor imaging.

Nucleosome autoantibodies

The nucleosome is a large protein-nucleic acid complex involved in DNA packing and in controlling genetic information. Under circumstances described below, this component, normally sequestered in the cell nucleus, is released into the extracellular milieu and then is easily accessible to cells of the immune system. For still not completely understood reasons, nucleosomes become immunogenic under particular conditions. Thus, anti-nucleosome autoantibodies (autoAb) have been described in connective tissue diseases and especially in systemic lupus erythematosus (SLE). This review describes the mechanisms leading to nucleosome production and anti-nucleosome autoimmunity, as well as the pathogenesis associated with nucleosomes.

Monoclonal antibody 2C5-mediated binding of liposomes to brain tumor cells in vitro and in subcutaneous tumor model in vivo

This study aimed to investigate the monoclonal antibody (mAb) 2C5 with nucleosome-restricted specificity for its ability to specifically recognize human brain tumor cells and to serve as a specific ligand for liposome targeting to brain tumor cells in vitro and in vivo. The affinity of mAb 2C5 towards brain tumor cells was tested by flow cytometry. The interaction of 2C5-immunoliposomes (ILS) with brain tumor cells in vitro was studied by fluorescence microscopy. For in vivo accumulation studies, (111)In-ILS were administered i.v. into mice bearing subcutaneously grown brain tumor. mAb 2C5 was found to be reactive against several tested brain tumor cell lines. mAb 2C5 and 2C5-ILS demonstrated enhanced cell-surface binding with CCF-STTG1,U-87 MG and LN-18 cells in vitro. 2C5-ILS displayed significantly better accumulation in the subcutaneously grown brain tumor than non-specific control IgG-ILS. mAb 2C5 specifically recognizes brain tumor cells and can serve as a ligand to target drug carriers such as liposomes to brain tumor cells in vivo.

Pathogenic autoantibodies: emerging insights into tissue injury

Accumulating evidence is emerging that B lymphocytes and autoantibodies are critical in the development of autoimmune disease. Even in certain disorders initially thought to be T cell-mediated, these immune components are now considered key players in the disease pathogenesis, and new autoantibody specificities have been added to the growing list of targets including cell surface receptors and ion channels that may be involved in a variety of neuropsychiatric and cardiovascular disorders. Studies of autoantibodies penetrating living cells suggest a dosage effect in generating a biological outcome in vivo. Some autoantibodies, such as those directed to double-stranded DNA, can bind to a variety of surrogate antigens located in different cellular compartments, and this may have different biological consequences. This polyreactive behavior could be related to their conformational diversity, or to the fact that the epitope recognized is distributed among other macromolecular antigens. In addition, recent studies revealed unsuspected mechanisms of pathogenesis, wherein autoantibodies have been described that can activate neuronal, endothelial cells or B lymphocytes. Other autoantibodies inactivate the target antigens, or exhibit a catalytic activity, releasing toxic oxygen products that may be linked to arthritic or atherosclerotic injury.

Interspecific structural differences in nucleosome as revealed by heteroimmunization in mice with human nucleosome

Although mounting evidence suggests the association of anti-nucleosome (NS) antibodies with lupus nephropathy in humans, the influence of interspecific differences in NS structure on the diagnosis has not been studied fully. Thus, we investigated the interspecific differences in NS structure by immunizing normal BALB/c mice with human nucleosomes (hNS). We purified hNS and mouse nucleosomes (mNS) from individual established cell lines. Purified NS was of high-pressure liquid chromatography grade and contained less than 1% dinucleosome, if any. Immune responses to NS were tested by an enzyme-linked immunosorbent assay. Of 6 mice, 2 responded to both hNS and mNS. However, antibodies produced in individual mice had higher affinity to mNS than to hNS. IgG response to hNS was IgG1 and IgG2b in subclass, whereas that to mNS was restricted to IgG1. Coincident with this response difference, agarose gel electrophoresis showed a mobility difference between hNS and mNS: the former was slower than the latter. In conclusion, immunodifferentiation in vivo in mice of autologous from heterologous NS together with their mobility difference in agarose gel suggest the presence of interspecific differences in NS. In humans, 2 out of 14 randomly tested patients with systemic lupus erythematosus preferred hNS over mNS; the IgG subclass in one was IgG1, and in the other IgG4. Taken together, interspecific differences in NS will provide a new area of study not only in biochemistry but also in immunology and/or autoimmunity.

Tumor-targeted liposomes: doxorubicin-loaded long-circulating liposomes modified with anti-cancer antibody

Commercially available doxorubicin-loaded long-circulating liposomes (Doxil, Alza Pharmaceuticals) were modified with the monoclonal nucleosome (NS)-specific 2C5 antibody (mAb 2C5) that recognizes a broad variety of tumors via the tumor cell surface-bound NSs. For incorporation into liposomes, mAb 2C5 was modified with poly(ethylene glycol)-phosphatidyl ethanolamine conjugate (PEG-PE) with the free PEG terminus activated with the p-nitrophenylcarbonyl group (pNP-PEG-PE). Derivatives of mAb 2C5 containing a variable number of PEG-PE residues (10-32) per protein molecule were prepared with a reasonably good preservation of the antibody specific activity even at the highest degree of modification. PEG-PE-modified antibody quantitatively incorporated into the liposomal membrane of doxorubicin-loaded liposomes with a loss of not more than 20% of the encapsulated doxorubicin. 2C5-targeted Doxil liposomes acquired the ability to recognize NSs and specifically bind to various tumor cells. Doxorubicin-loaded long-circulating liposomes modified with the mAb 2C5 kill various tumor cells in vitro with the efficiency higher than non-targeted doxorubicin-loaded liposomes.

Antinucleosome autoantibodies bind directly to cell lines in vitro and via the FcgammaRIIB receptor to B lymphocytes in vivo: a role for immune complexes in interactions between antinucleosome IgG2a and B cells of BXSB lupus mice

The initial novel observation of this study was that most B cells of male BXSB lupus mice bear surface IgG2a(b) of extrinsic origin. To define the surface antigen, we here examine three (NZBxBXSB)F1-derived IgG2a(b) monoclonal antibodies (mAbs) selected for binding to cell surfaces. Surprisingly, all three mAbs bound the nucleosome (nuc) particle, the fundamental unit of chromatin and an early target of autoimmunity in systemic lupus erythematosus. Their tentative dissociation constant (K(d)) for soluble nuc particles was approximately 7 x 10(-10) m. The mAbs bound more weakly to both H2A-H2B-DNA and H3-H4-DNA complexes, and in immunoblot they stained all four core histones. The mAbs detected a surface antigen on all cell lines examined, present on viable cells. When stripped of nuc, and in the presence of DNase I, their binding to cell lines improved. Heparin displaced the antigen from the cell surface. In vivo, the three mAbs stained B cells of several BALB/c mice clearly stronger than the isotype control; this differential staining was significantly reduced in FcgammaRIIB-deficient mice. The results indicate that the three mAbs recognize (a) planted antigen on viable cultured cells and (b) soluble autoantigen in vivo, leading to immune complexes that bind to FcgammaRIIB. Further experiments demonstrated that antinuc IgG2a could be eluted from splenocytes of a male BXSB lupus mouse. Hence, at least part of the extrinsic IgG2a(b) found on BXSB B cells may represent FcgammaRIIB-bound nuc-IgG2a(b) complexes.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

OBJECTIVE

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

DESIGN

Laboratory research study with comparison group.

SETTING

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

SUBJECTS

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

INTERVENTIONS

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

MAIN OUTCOME MEASURES

Nucleosome level by treatment.

RESULTS

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

CONCLUSIONS

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

Antibodies to a cell surface histone-like protein protect against Histoplasma capsulatum

A protective role for antibodies has not previously been described for host defense against the pathogenic fungus Histoplasma capsulatum (Hc). Mouse mAb's were generated from mice immunized with Hc yeast that binds the cell surface of Hc. Administration of mAb's before Hc infection reduced fungal burden, decreased pulmonary inflammation, and prolonged survival in a murine infection model. Protection mediated by mAb's was associated with enhanced levels of IL-4, IL-6, and IFN-gamma in the lungs of infected mice. The mAb's increased phagocytosis of yeast by J774.16 cells through a CR3-dependent process. Ingestion of mAb-opsonized Hc by J774.16 macrophage-like cells was associated with yeast cell growth inhibition and killing. The mAb's bound to a 17-kDa antigen expressed on the surface of Hc. The antigen was identified as a histone H2B-like protein. This study establishes that mAb's to a cell surface protein of Hc alter the intracellular fate of the fungus and mediate protection in a murine model of lethal histoplasmosis, and it suggests a new candidate antigen for vaccine development.

Effect of cytofectins on the immune response of murine macrophages to mammalian DNA

DNA, depending on base sequence, can induce a wide range of immune responses. While bacterial DNA is stimulatory, mammalian DNA is inactive alone and can, moreover, inhibit the response to bacterial DNA. To determine whether the mode of cell entry affects the immune properties of mammalian DNA, we have investigated the effects of the cytofectin agents Fugene 6 (Roche Diagnostics Corp., Indianapolis, IN), Lipofectin and Lipofectamine (Life Technologies, Grand Island, NY) on the responses of murine macrophages to DNA from calf thymus and human placenta. Whereas calf thymus and human placenta DNA alone failed to stimulate J774 or RAW264.7 cell lines or bone marrow-derived macrophages, these DNAs in complexes with cytofectin agents stimulated macrophages to produce nitric oxide but not interleukin 12. Both single-stranded and double-stranded DNAs were active in the presence of cytofectins. Macrophage activation by the DNA-cytofectin complexes was reduced by chloroquine, suggesting a role of endosomal acidification in activation. As shown by flow cytometry and confocal microscopy, the cytofectins caused an increase in the uptake of DNA into cells. Our findings indicate that macrophages vary in their response to DNA depending on uptake pathway, suggesting that activation by DNA reflects not only sequence but also context or intracellular location.

Concomitant early appearance of anti-ribonucleoprotein and anti-nucleosome antibodies in lupus prone mice

OBJECTIVE

To gain insights on initial stages of the autoimmune response in lupus prone mice taking advantage of new sensitive and quantitative techniques for the detection of autoantibodies specific for RNA- (ribonucleoproteins) and DNA-protein (chromatin) complexes.

METHODS

DNA and nucleosome antibodies were detected by ELISA, antibodies to SmB, U1A-RNP, Ro52, Ro60 and La by a new radioligand assay, using de novo synthesized radio-labeled antigens.

RESULTS

Analysis of anti-chromatin (including anti-nucleosome, anti-dsDNA and anti-histone antibodies) and of anti-snRNP antibodies (including anti-U1A-RNP, anti-SmB, anti-Ro52, anti-Ro60, anti-La antibodies) was performed in sequential sera from B/W, MRL+/+, MRL Yaa and MRL lpr/lpr mice. In a cohort of 105 MRL+/+ mice of different ages, 59, 51, and 57 mice were positive for anti-nucleosome, anti-SmB and anti-U1A-RNP, respectively. None of them was positive for anti-dsDNA. Importantly, antibody positivities were not randomly distributed but were significantly clustered in individual mice. Appearance of DNA- and RNA-protein complex antibodies started at approximately 18-20 weeks of age, preceding that of the anti-dsDNA (or anti-histone) antibodies that only started at 30-32 weeks. Anti-nucleosome, anti-SmB and anti-U1A-RNP antibody responses did not display any cross-reactivity as demonstrated by inhibition and adsorption experiments.

CONCLUSION

These data indicate that anti-nucleosome and anti-snRNP antibodies appear early and concomitantly in lupus prone mice even though they do not share any cross-reactivity. These results fit with the assumption that their production is triggered by tightly physically associated nucleosomes and snRNP autoantigens contained in the same apoptotic bodies.

Antinuclear autoantibodies as potential antineoplastic agents

The immune system confines neoplasia at various stages of tumor development. Whereas the role of cellular immunity has been investigated widely and utilized in the clinic, the importance of humoral immunity in this process has begun to emerge only in recent years. Circulating antinuclear autoantibodies (ANAs) typically found in autoimmune conditions, have also been detected in cancer patients and in healthy elderly individuals. The pathogenic role of ANAs in autoimmunity is well studied; however, little research has been carried out to elucidate the functions of ANAs in cancer patients. Experimental data favoring the antitumor activity of ANAs might support the clinical testing of monoclonal ANAs as a cancer therapy, if confirmed by further experiments.

DNA and heparin alter the internalization process of anti-DNA monoclonal antibodies according to patterns typical of both the charged molecule and the antibody

The internalization into CHO-K1 fibroblasts of three polyreactive monoclonal IgG2a anti-DNA autoantibodies (mAbs), F14.6, J20.8 and F4.1, isolated from the same unimmunized (NZBxNZW) F1 mouse, and synthetic peptides derived from F4.1 was studied using a technique which quantifies nuclear accumulation. The localization of the mAbs was intranuclear. We compared the influence of two negatively-charged molecules, DNA or heparin. At low concentrations, DNA had dual effects-inhibitory or stimulatory-depending on the mAb. Heparin was inhibitory or had no effect. The possibility that proteoglycans are 'receptors' recognized by anti-DNA mAbs which bind through heparin-sensitive reactions, was explored. Only F4.1 internalization was partly inhibited in glycosaminoglycan-deficient cells. We propose that the complex alterations of internalization patterns of these polyreactive mAbs by the two negatively charged molecules can be explained by (a) the potential of polyreactive mAbs to bind to various charge (or conformation-) dependent 'receptors', (b) the potential of a subclass of mAbs complexed with DNA to utilize additional 'receptor(s)'. Glycosaminoglycans were required for internalization of F4.1-derived peptides, which remained extranuclear, suggesting that nuclear internalization of mAb F4.1 is a multistep process that requires certain sequences present on the intact mAb.

Calreticulin, a potential cell surface receptor involved in cell penetration of anti-DNA antibodies

A 50-kDa protein was purified as a potential receptor, using an affinity matrix containing biotinylated F14.6 or H9.3 anti-DNA mAbs derived from autoimmune (New Zealand Black x New Zealand White)F(1) mouse and membrane extracts from cells. This protein was identified as calreticulin (CRT) by microsequencing. Confocal microscopy and FACS analysis showed that CRT was present on the surface of various cells. CRT protein was recognized by a panel of anti-DNA mAbs in ELISA. The binding of F14.6 to lymphocytes and Chinese hamster ovary cells was inhibited by soluble CRT or SPA-600. Thus, the anti-DNA mAbs used in this study bound to CRT, suggesting that CRT may mediate their penetration into the cells and play an important role in lupus pathogenesis.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

Overlap of the anti-cardiolipin and anti-nucleosome responses of the (NZW X BXSB)F1 mouse strain: a new pattern of cross-reactivity for lupus-related autoantibodies

The association of anti-nuclear antigen (ANA) and anti-cardiolipin (CL) antibodies is often observed during systemic lupus erythematosus (SLE) or the primary anti-phospholipid syndrome, thereby raising the possibility of a relationship between these two autoantibody populations. To determine whether ANA and anti-CL antibodies can overlap, we derived, from a male (NZW x BXSB)F1 mouse, 14 hybridomas selected based on their capacities to react with CL and to label HEp-2 cell nuclei. Four of these anti-CL were IgG and bound to CL and phosphatidylserine in a cofactor-dependent manner and reacted strongly with nucleosomes. Variable region sequence analysis indicated that these four monoclonal antibodies (mAb) were derived from three independent B cell clones that used recurrent heavy and/or light chain immunoglobulin rearrangements, as assessed by comparison with each other and prototypic anti-CL mAb previously derived from different lupus mouse strains. These results indicate that anti-CL mAb can have overlapping cross-reactivities with nucleosomes, thereby defining a new category of SLE-related autoantibodies characterized by their capacities to recognize distinct supramolecular complexes, formed by the association of an anionic structure and a protein, that exert a strong selective pressure on autoreactive B cell clones.

Presence of antinucleosome autoantibodies in a restricted set of connective tissue diseases: antinucleosome antibodies of the IgG3 subclass are markers of renal pathogenicity in systemic lupus erythematosus

OBJECTIVE

To study the frequency and disease specificity of antinucleosome antibody reactivity in diverse connective tissue diseases (CTD), and to determine factors, such as antibody subclass, that may influence the pathogenicity of these antibodies in relation to disease activity.

METHODS

IgG and IgM antinucleosome activities on nucleosome core particles from 496 patients with 13 different CTD and 100 patients with hepatitis C were measured by enzyme-linked immunosorbent assay (ELISA). Of the patients with CTD, 120 had systemic lupus erythematosus (SLE), 37 had scleroderma (systemic sclerosis; SSc), 20 had mixed connective tissue disease (MCTD), and 319 had other CTD, including Sjögren's syndrome, inflammatory myopathy, rheumatoid arthritis, primary antiphospholipid syndrome, Wegener's granulomatosis, Takayasu arteritis, giant cell arteritis, relapsing polychondritis, Behçet's syndrome, and sarcoidosis. Antinucleosome-positive sera were further analyzed, by isotype-specific ELISA, for antinucleosome and anti-double-stranded DNA (anti-dsDNA) IgG subclasses.

RESULTS

SLE, SSc, and MCTD were the only 3 CTD in which antinucleosome IgG were detected (71.7%, 45.9%, and 45.0% of patients, respectively). Antinucleosomes of the IgG3 subclass were present at high levels in patients with active SLE and were virtually absent in those with SSc, MCTD, or inactive SLE, and their levels showed a positive correlation with SLE disease activity. Of note, an increase in levels of antinucleosome of the IgG3 isotype was observed during SLE flares, and this increase was found to be closely associated with active nephritis. Levels of antinucleosome of the IgG1 subclass showed a trend toward an inverse correlation with SLE disease activity. No significant fluctuation in the anti-dsDNA isotype profile was observed in relation to SLE severity or clinical signs.

CONCLUSION

Our data suggest that IgG antinucleosome is a new marker that may help in the differential diagnosis of CTD; antinucleosome of the IgG3 isotype might constitute a selective biologic marker of active SLE, in particular, of lupus nephritis.

Anti-Double-Stranded DNA Antibodies and Immunostimulatory Plasmid DNA in Combination Mimic the Endogenous IFN-α Inducer in Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE) have increased blood levels of IFN-α, which correlate to disease activity. We previously identified an IFN-α-inducing factor (IIF) in the blood of SLE patients that activated the natural IFN-α-producing cells in cultures of normal PBMC. The SLE-IIF contained DNA and IgG, possibly as small immune complexes. In our study, we demonstrated that SLE-IIF correlated to the presence of anti-dsDNA Abs in patients and contained anti-dsDNA Abs as an essential component. Purified anti-DNA Abs or SLE-IgG caused only a weak IFN-α production in cultures of normal PBMC in the presence of costimulatory IFN-α2b. However, they converted the plasmid pcDNA3, which itself induced no IFN-α production in PBMC, into an efficient IFN-α inducer. A human monoclonal anti-ss/dsDNA Ab had the same effect. This IFN-α-inducing activity of the plasmid was abolished by methylation, suggesting that unmethylated CpG DNA motifs were important. Like IIF in SLE serum, the combination of SLE-IgG and pcDNA3 appeared to stimulate IFN-α production in natural IFN-α-producing cells, a unique cell population resembling immature dendritic cells. The IFN-α production was greatly enhanced by IFN-α2b and IFN-β, and for SLE-IIF it was also enhanced by GM-CSF but inhibited by IL-10. We have therefore identified a new function of DNA-anti-DNA Ab complexes, IFN-α induction, that might be important in the pathogenesis of SLE.

Granulocyte-Colony Stimulating Factor Treatment of Lupus Autoimmune Disease in MRL-lpr/lpr Mice

G-CSF not only functions as an endogenous hemopoietic growth factor for neutrophils, but also displays pro-Th2 and antiinflammatory properties that could be of therapeutic benefit in autoimmune settings. We evaluated the effect of treatment with G-CSF in a murine model of spontaneous systemic lupus erythematosus, a disease in which G-CSF is already administered to patients to alleviate neutropenia, a common complication. Chronic treatment of lupus-prone MRL-lpr/lpr mice with low doses (10 μg/kg) of recombinant human G-CSF, despite the induction of a shift toward the Th2 phenotype of the autoimmune response, increased glomerular deposition of Igs and accelerated lupus disease. Conversely, high-dose (200 μg/kg) treatment with G-CSF induced substantial protection, prolonging survival by >2 mo. In the animals treated with these high doses of G-CSF, neither the Th1/Th2 profile nor the serum levels of TNF-α and IL-10 were modified. Despite the presence of immune complexes in their kidney glomeruli, no inflammation ensued, and serum IL-12 and soluble TNF receptors remained at pre-disease levels. This uncoupling of immune complex deposition and kidney damage resulted from a local down-modulation of FcγRIII (CD16) expression within the glomeruli by G-CSF. Our results demonstrate a beneficial effect of high doses of G-CSF in the prevention of lupus nephritis that may hold promise for future clinical applications, provided caution is taken in dose adjustment.

Small-bowel involvement in systemic lupus erythematosus: a morphometric and immunohistochemical study

BACKGROUND

We have investigated the intestinal mononuclear cell subpopulations in patients with systemic lupus erythematosus (SLE) and correlated these with the disease activity.

METHODS

Eighteen female outpatients were studied; in 10 of them lupus activity was measured with the Lupus Activity Criteria Count and the SLE Disease Activity Index. Eight patients were in lupus remission. The control group consisted of 10 healthy volunteers. Peroral jejunal biopsy was performed in all individuals, at the angle of Treitz, using a Watson capsule, under X-ray control. Histologic studies analysed the villous to crypt ratio, lamina propria cells, and intraepithelial lymphocyte count. Immunohistochemical evaluation was carried out with the indirect immunoperoxidase technique, using monoclonal antibodies against CD3, CD4, CD8, D1, D7, D9, and M1.

RESULTS

Lamina propria CD3+, CD8+, D7+, and M1+ cells from patients with SLE did not differ significantly from those of controls. CD4+ cells were decreased in all patients with SLE, especially in the clinically inactive patients. D1+ and D9+ cells were also decreased in all patients.

CONCLUSION

The finding of quantitative abnormalities in the cell-mediated immunity of the intestinal mucosa may reflect systemic defects of the immune system in SLE.

Chromatin clearance in C57Bl/10 mice: interaction with heparan sulphate proteoglycans and receptors on Kupffer cells

Chromatin is an important autoantigen in the pathogenesis of systemic lupus erythematosus (SLE) as an immunogen and as a part of nephritogenic immune complexes. Earlier studies focused on clearance of DNA. However, DNA released into the circulation from dying cells is found associated with histones in nucleosomes. The liver is the major organ involved in clearance of chromatin from the circulation of mice. Heparan sulphate proteoglycans (HSPG) have been implicated in the clearance of various charged molecules. Receptor-mediated clearance of ssDNA by the liver has also been reported. Because chromatin contains positively charged histones in addition to DNA, we wished to determine if HSPG and/or DNA receptors are involved in chromatin clearance. The rate of clearance of H1-stripped chromatin from the bloodstream of C57Bl/10 mice was markedly decreased by prior treatment of mice with Heparinase I. Clearance was also inhibited by heparin, heparan sulphate, and DNA, but not by colominic acid. DNA was the most effective inhibitor of clearance and released chromatin from sites of clearance. Depletion of Kupffer cells and splenic macrophages using liposome-encapsulated Clodronate (dichloromethylene bisphosphonate) markedly inhibited chromatin clearance. These data suggest that chromatin clearance is mediated by charge interactions with cell surface HSPG and by DNA receptors. Clearance and degradation of chromatin require functional macrophages in the liver and spleen.

Nucleosomes bind to cell surface proteoglycans

Material on the surface of activated T-cells was displaced following incubation with a sulfated polysaccharide, dextrin 2-sulfate (D2S), and purified by anion-exchange chromatography. This revealed a complex comprising histones H2A, H2B, H3, and H4 and DNA fragmented into 180-base pair units characteristic of mono-, di-, tri, and polynucleosomes, a pattern of fragmentation similar to that found in apoptotic cells. An antibody raised against the purified nucleosome preparation bound to the plasma membrane of activated T-cells confirming the surface location of nucleosomes. The interaction of sulfated polysaccharides with nucleosomes was investigated using a biotinylated derivative of D2S. It was found that sulfated polysaccharides bound to nucleosomes via the N termini of histones, especially H2A and H2B. Treatment of T-cells with either heparinase or heparitinase abolished nucleosome binding to plasma membranes. This suggests that nucleosomes are anchored to the surface of T-cells by heparan sulfate proteoglycans through an ionic interaction with the basic N-terminal residues in the histones. Furthermore, nucleosomes bound to the cell surface in this manner are then able to bind other sulfated polysaccharides, such as D2S, heparin, or dextran sulfate, through unoccupied histone N termini forming a complex comprising cell surface heparan sulfate proteoglycans, nucleosomes, and sulfated polysaccharides.

A Central Role for αβ T Cells in the Pathogenesis of Murine Lupus

We have previously shown that female transgenic mice expressing IFN-γ in the epidermis, under the control of the involucrin promoter, develop inflammatory skin disease and a form of murine lupus. To investigate the pathogenesis of this syndrome, we generated female IFN-γ transgenic mice congenitally deficient in either αβ or γδ T cells. TCRδ−/− transgenics continued to produce antinuclear autoantibodies and to develop severe kidney lesions. In contrast, TCRβ−/− IFN-γ transgenic mice failed to produce antinucleosome, anti-dsDNA, or antihistone autoantibodies, and kidney disease was abolished. Both αβ- and γδ-deficient transgenics continued to develop IFN-γ-associated skin disease, lymphadenopathy, and splenomegaly. The data show that the autoantibody-mediated pathology of murine lupus in IFN-γ transgenic mice is completely αβ T cell dependent and that γδ T cells cannot drive autoantibody production. These results imply that production of antinuclear autoantibodies in IFN-γ transgenic animals is Ag driven, and we identified clusters of apoptotic cells in the epidermis of the mice as a possible source of self Ags. Our findings emphasize the relevance of this murine lupus model to the human disease.