CpG DNA: a pathogenic factor in systemic lupus erythematosus?

Induction of autoantibody production but not autoimmune disease in HEL transgenic mice vaccinated with HEL in combination with CpG or control oligodeoxynucleotides

CpG oligodeoxynucleotides (ODN) are synthetic DNA sequences that mimic bacterial DNA, and bind to the TLR9 receptor. The cells that express TLR9, B cells and dendritic cells, are stimulated by CpG ODN and induce innate and acquired immune responses. Because CpG ODN induce antigen-independent immune activation there has been much interest in the possibility that they may break self tolerance. To test this hypothesis we used a tolerance model with hen egg lysozyme (HEL)-transgenic (Tg) mice, anti-HEL Ig-Tg mice and double (Dbl)-Tg mice injected with CpG ODN alone or together with HEL self antigen. When cultured in vitro, tolerant B cells responded to CpG ODN in a similar way as the non-tolerant Ig-Tg B cells in terms of cell proliferation, NFkappaB activation and CD69 expression. Despite these potent in vitro stimulatory effects of CpG ODN alone, HEL-Tg mice injected with CpG ODN alone, or in combination with low dose antigen (4 microg HEL), surprisingly did not produce any detectable anti-HEL Ab. However, HEL-Tg or Dbl-Tg mice immunized with CpG ODN plus higher doses of self antigen showed strong antigen-specific humoral responses. Surprisingly, control non-CpG ODN also had partial activity for breaking tolerance and inducing autoantibody production when administered in combination with self antigen, though not when used alone. Despite the production of high titers of anti-HEL Ab in the immunized HEL-Tg mice, no evidence of autoimmune disease was detected. We conclude that immunization with CpG or control ODN in the presence of a high dose of exogenous self antigen, but not treatment with ODN alone, can break tolerance to self antigen without inducing autoimmune disease in this system.

Use of CpG oligodeoxynucleotides as immune adjuvants

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs directly stimulate human B cells and plasmacytoid dendritic cells (pDCs), thereby promoting the production of T helper 1 (Th1) and pro-inflammatory cytokines and the maturation/activation of professional antigen-presenting cells. These activities enable CpG ODNs to act as immune adjuvants, accelerating and boosting antigen-specific immune responses by 5-500-fold. These effects are optimized by maintaining close physical contact between the CpG DNA and the immunogen. Animal challenge models establish that protective immunity can be accelerated and magnified by coadministering CpG DNA with vaccines. Ongoing clinical studies indicate that CpG ODNs are safe and well tolerated when administered as adjuvants to humans, and in some cases, they increase vaccine-induced immune responses.

Apoptosis and systemic lupus erythematosus

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

Synthetic CpG oligodeoxynucleotides accelerate the development of lupus nephritis during preactive phase in NZB x NZWF1 mice

The effect of synthetic CpG-oligodeoxynucleotides (CpG-ODN) on the development of lupus nephritis during preactive phase (within seven months of age) in autoimmune lupus NZB x NZWF1 (B/WF1) mice was examined. Treatment of CpG-ODN was started at the age of 2.75 months and continued until 6.25 months. Overt disease began at the age of six months and progressed linearly at the age of 6.75 months in CpG-ODN-treated, but not control ODN-treated (control) groups. Also compared to control group, CpG-ODN-treated mice exhibited a severe glomerulonephritis (GN), with prominent deposits of IgG2a and C3, which paralleled increased titre of IgG2a type anti-nuclear antibody in the blood. Among several cytokines (interleukin, IL-6, IL-4, IL-1alpha, IL-10, interferon-gamma and tumor necrosis factor-alpha) in blood, IL-6 production paralleled the development of lupus nephritis. The present study suggests that CpG-ODN may enhance IL-6 production. The role of IL-6 in the development of GN will be discussed.

Activation of toll-like receptor-9 induces progression of renal disease in MRL-Fas(lpr) mice

How bacterial or viral infections trigger flares of autoimmunity is poorly understood. As toll-like receptor (TLR)-9 activation by exogenous or endogenous CpG-DNA may contribute to disease activity of systemic lupus erythematosus, we examined the effects of CpG-oligodeoxynucleotides (ODN) or DNA derived from Escherichia coli (E. coli) on the course of nephritis in MRL(lpr/lpr) mice. In kidneys of these mice, TLR9 localized to glomerular, tubulointerstitial, and perivascular infiltrates. After intraperitoneal injection labeled CpG-ODN localized to glomerular and interstitial macrophages and dendritic cells in nephritic kidneys of MRL(lpr/lpr) mice but not in healthy MRL controls. Furthermore, murine J774 macrophages and splenocytes from MRL(lpr/lpr) mice, but not tubular epithelial cells, renal fibroblasts, or mesangial cells, expressed TLR9 and up-regulated CCL5/RANTES mRNA upon stimulation with CpG-ODN in vitro. In vivo both E. coli DNA and CpG-ODN increased serum DNA autoantibodies of the IgG2a isotype in MRL(lpr/lpr) mice. This was associated with progression of mild to crescentic glomerulonephritis, interstitial fibrosis, and heavy proteinuria. CpG-ODN increased renal CCL2/MCP-1 and CCL5/RANTES expression associated with increased glomerular and interstitial leukocyte recruitment. In contrast control GpC-ODN had no effect. We conclude that TLR9 activation triggers disease activity of systemic autoimmunity, for example, lupus nephritis, and that adaptive and innate immune mechanisms contribute to the CpG-DNA-induced progression of lupus nephritis.

The putative role of apoptosis-modified histones for the induction of autoimmunity in Systemic Lupus Erythematosus

In recent years, it has become evident that Systemic Lupus Erythematosus (SLE) is a disease characterized by an array of autoantibodies directed against the native nucleosome, its DNA component and/or its histone component. Nuclear antigens are generated and released in vivo during apoptosis. A hallmark of apoptosis is the cleavage of chromatin by caspase-activated DNase. This fragmentation occurs at the internucleosomal level and leads to DNA ladder formation classically associated with apoptosis. Thus, dysregulation of DNA fragmentation might be directly linked to the induction of autoimmunity in SLE. In our studies, activated human lymphoblasts contain high amounts of core histones in their cell lysates after apoptosis induction. This accumulation correlated highly with markers of early apoptosis (Annexin V positive, propidium iodide negative), but not with markers of late apoptosis or necrosis. Interestingly, accumulation of core histones or nucleosomes in cell lysates was detected as early as 30 or 60 min after UV irradiation, whereas phosphatidylserine externalization occurred 2 hr after apoptosis induction. Our results suggest that extranuclear accumulation of core histones is a very early event in apoptosis, preceding the externalization of phagocytosis signals on the outer membrane surface of apoptotically dying lymphoblasts. The following review will discuss these results in a broader perspective which includes our hypothesis of how apoptosis dysregulation during early phases may contribute to the induction of autoimmunity against nuclear autoantigens as seen in SLE.

DNA methylation in systemic lupus erythematosus

Recent studies on epigenetics, including DNA methylation and its regulatory enzymes, seem likely to contribute to elucidation of the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE), although the relationship between DNA methylation and SLE has long been the subject of investigation. To obtain a deeper understanding of the role of DNA methylation in the induction of SLE, we reviewed the relationship between DNA methylation and SLE based on findings reported in the literature and our own data. Various studies, including ours, have indicated the possible importance of DNA methylation, especially hypomethylation, in the etiology of SLE. These epigenetic studies may give us clues towards elucidation of the pathogenesis of SLE and development of new therapeutic strategies for this disease.

Repetitive elements in mammalian telomeres suppress bacterial DNA-induced immune activation

Bacterial DNA contains immunostimulatory CpG motifs that trigger an innate immune response capable of promoting host survival following infectious challenge. Yet CpG-driven immune activation may also have deleterious consequences, ranging from autoimmune disease to death. We find that repetitive elements present at high frequency in mammalian telomeres, but rare in bacteria, down-regulate CpG-induced immune activation. Suppressive activity correlates with the ability of telomeric TTAGGG repeats to form G-tetrads. Colocalization of CpG DNA with Toll-like receptor 9 in endosomal vesicles is disrupted by these repetitive elements, although cellular binding and uptake remain unchanged. These findings are the first to establish that specific host-derived molecules can down-regulate the innate immune response elicited by a TLR ligand.

Immunostimulatory CpG oligodeoxynucleotides and antibody therapy of cancer

Synthetic oligodeoxynucleotides containing CG motifs (CpG ODN) have potent immunostimulatory properties, and have potential as immunotherapeutic agents in cancer. Animal models suggest CpG ODN can activate a variety of immune effector cells such as natural killer (NK) cells, and also enhance the efficacy of tumor immunization when used as immune adjuvants or to directly activate antigen-presenting cells. CpG ODN are also capable of altering the expression of a number of antigens by malignant B-cells, including those targeted by monoclonal antibodies (moAbs) and those involved in communication with T cells. The ability of CpG ODN to activate the immune effector cells that participate in antibody-dependent cellular cytotoxicity (ADCC), upregulate target antigen, and perhaps induce development of an active immune response, suggest these agents may be capable of enhancing the efficacy of antitumor moAb therapy. Such enhanced efficacy has been demonstrated in animal models and is now undergoing evaluation in clinical trials.

Innate immune responses in lupus-prone Palmerston North mice: differential responses to LPS and bacterial DNA/CpG oligonucleotides

Inadequate immune response to infectious danger may contribute to the pathogenesis of systemic autoimmune diseases, e.g., systemic lupus erythematosus. To test this hypothesis, we studied innate responses of prediseased lupus-prone Palmerston North (PN) mice to lipopolysaccharide (LPS), bacterial DNA, and synthetic CpG oligonucleotides. LPS and bacterial DNA/CpG oligodeoxyribonucleotides (ODNs) drove PN splenocytes into the cell cycle and protected B cells against spontaneous apoptosis, as in control lupus-free DBA-1 mice. LPS induced significantly higher IL-6 production in PN than in control splenocytes. In contrast, in PN splenocytes bacterial DNA and CpG ODNs induced approximately four- to sixfold lower IL-12p40 and approximately twofold lower IL-6 secretion than controls. This reduction in cytokine secretion in PN mice was not due to delayed kinetics but was related to significantly higher constitutive and CpG-inducible IL-10 secretion. Neutralizing anti-IL-10 antibodies almost completely restored PN IL-6 and IL-12p40 secretion to DBA-1 levels, whereas exogenous IL-10 inhibited in vitro IL-6 and IL-12p40 production in DBA-1 mice. Importantly, treatment with either IL-10 or anti-IL-10 antibody did not modulate CpG-induced cell cycle entry and apoptosis protection in either strain. In conclusion, lupus-prone PN mice show abnormal innate responses through their pattern-recognition TLR9 receptors, characterized by higher inducible IL-10 and lower IL-12p40 and IL-6 secretion, thus implying that response to infectious danger in PN mice is inappropriate and may be linked to lupus pathogenesis.

Identification and characterization of SmD183-119-reactive T cells that provide T cell help for pathogenic anti-double-stranded DNA antibodies

OBJECTIVE

The C-terminal peptide of amino acids 83-119 of the SmD1 protein is a target of the autoimmune response in human and murine lupus. This study was undertaken to test the hypothesis that SmD1(83-119)-reactive T cells play a crucial role in the generation of pathogenic anti-double-stranded DNA (anti-dsDNA) antibodies.

METHODS

Splenic or lymph node T cells derived from unmanipulated as well as SmD1(83-119)-immunized NZB/NZW mice were analyzed in vitro by enzyme-linked immunospot (ELISpot) assay to determine T cell help for anti-dsDNA generation induced by the SmD1(83-119) peptide. Cytokines expressed by these T cells were measured by ELISpot assay, enzyme-linked immunosorbent assay, and flow cytometry. SmD1(83-119)- and ovalbumin-specific T cell lines were generated and characterized.

RESULTS

The SmD1(83-119) peptide, but not the control peptides, significantly increased the in vitro generation of anti-dsDNA antibodies in cultures from unmanipulated NZB/NZW mice. Interferon-gamma (IFNgamma), interleukin-2 (IL-2), IL-4, transforming growth factor beta, and IL-10 production increased in response to the peptide in young mice; only IFNgamma and IL-2 were increased in older, diseased mice. Activation of SmD1(83-119)-reactive T cells by immunization of NZB/NZW mice resulted in elevated anti-dsDNA synthesis and, later, increased antibodies to SmD1(83-119). Most cells in SmD1(83-119)-specific CD4+ T cell lines helping both antibodies had increased intracellular expression of IFNgamma, and most expressed both IFNgamma and IL-4.

CONCLUSION

The SmD1(83-119) peptide plays an important role in generating T cell help for autoantibodies, including anti-dsDNA, and activates different subsets of T cells as defined by distinct cytokine expression. This peptide is an interesting target structure for the modulation of autoreactive T cells, and its characterization may contribute to our understanding of the role of autoantigen-reactive T cells in the pathogenesis of SLE.

Bacterial CpG-DNA aggravates immune complex glomerulonephritis: role of TLR9-mediated expression of chemokines and chemokine receptors

Immune complex glomerulonephritis (GN) often deteriorates during infection with viruses and bacteria that, in contrast to mammals, have DNA that contains many unmethylated CpG motifs. Balb/c mice with horse apoferritin-induced GN (HAF-GN) were treated with either saline, CpG-oligodeoxynucleotides (ODN), or control GpC-ODN. Only CpG-ODN exacerbated HAF-GN with an increase of glomerular macrophages, which was associated with massive albuminuria and increased renal MCP-1/CCL2, RANTES/CCL5, CCR1, CCR2, and CCR5 mRNA expression. CpG-ODN induced a Th1 response as indicated by serum anti-HAF IgG(2a) titers, mesangial IgG(2a) deposits, and splenocyte IFN-gamma secretion. Messenger RNA for the CpG-DNA receptor Toll-like reeptor 9 (TLR9) was present in kidneys with HAF-GN but not in normal kidneys. The source of TLR9 mRNA in HAF-GN could be infiltrating macrophages or intrinsic renal cells, e.g., mesangial cells; but, in vitro, only murine J774 macrophages expressed TLR9. In J774 cells, CpG-ODN induced the chemokines MCP-1/CCL2 and RANTES/CCL5 and the chemokine receptors CCR1 and CCR5. It is concluded that CpG-DNA can aggravate preexisting GN via a shift toward a Th1 response but also by a novel pathway involving TLR9-mediated chemokine and chemokine receptor expression by macrophages, which may contribute to the enhanced glomerular macrophage recruitment and activation. This mechanism may be relevant during infection-triggered exacerbation of human immune-complex GN and other immune-mediated diseases in general.

Extracellular mitochondrial DNA and oxidatively damaged DNA in synovial fluid of patients with rheumatoid arthritis

We investigated whether plasma and synovial fluid (SF) samples from patients with rheumatoid arthritis (RA) contained extracellular mitochondrial DNA (mtDNA) or the oxidatively damaged DNA adduct 8-hydroxy-2'-deoxyguanosine (8-oxodG). Moreover, we correlated the laboratory findings of the patients with RA with their levels of mtDNA and 8-oxodG. SF and plasma samples from 54 patients with RA, SF from 30 non-arthritic control subjects, and plasma from 22 healthy volunteers were collected. The samples were subjected to polymerase chain reaction (PCR) using mitochondrial genomic primers, and the products were analyzed by SDS-polyacrylamide-gel electrophoresis. The intensities of the PCR-amplified bands were quantified and normalized to a reference sample. Furthermore, the SF samples were assayed by enzyme-linked immunosorbent assay for 8-oxodG. Extracellular PCR-amplifiable mtDNA was detected in the SF of 38 of 54 (70%) patients with RA, but not in any of the SF controls. PCR-amplifiable mtDNA was detected in the plasma of 30 of 54 (56%) of patients with RA and in 6 of 22 (27%) of the healthy volunteers. The levels of mtDNA in the plasma and SF samples of patients with RA were significantly higher (P < 0.0001) than in the respective control samples. The presence of both mtDNA and 8-oxodG in SF was significantly correlated with the presence of rheumatoid factor in the patients with RA. Extracellular mtDNA and oxidized DNA were detected in the SF of the great majority of patients with RA, but were absent or present at low levels in the control SF. These findings indicate that endogenous nucleic acid compounds might participate in joint inflammation by activating immune cells in the joints to produce proinflammatory cytokines.

Effect of suppressive DNA on CpG-induced immune activation

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs stimulate a strong innate immune response. This stimulation can be abrogated by either removing the CpG DNA or adding inhibitory/suppressive motifs. Suppression is dominant over stimulation and is specific for CpG-induced immune responses (having no effect on LPS- or Con A-induced activation). Individual cells noncompetitively internalize both stimulatory and suppressive ODN. Studies using ODN composed of both stimulatory and suppressive motifs indicate that sequence recognition proceeds in a 5'-->3' direction, and that a 5' motif can block recognition of immediately 3' sequences. These findings contribute to our understanding of the immunomodulatory activity of DNA-based products and the rules that govern immune recognition of stimulatory and suppressive motifs.

The pathogenesis of autoimmune diseases

Autoimmunopathies are chronic inflammatory diseases which can be subdivided into several specificities on the ground of the clinical picture as well as serological findings and involvement of organ systems like the kidney, central nervous system or the hematopoietic system. The pathogenesis of these diseases is incompletely understood. With the exception of rare diseases in which the autoantigens are known, in the most frequent autoimmunopathies like rheumatoid arthritis or Systemic Lupus Erythematosus (SLE) only some partial aspects of the pathogenetic scenario are understood and rather well substantiated by experimental data. In RA, there are controversies concerning the central involvement of T-lymphocytes and/or synovial fibroblasts in the initiation of the diseases. It is meanwhile well known that TNF-alpha and possibly other related cytokines are involved at least in the perpetuation of the inflammatory cascades. Specific blockade of TNF-alpha leads to rapid improvement of RA disease activity and can prevent tissue destruction. An intriguing hypothesis postulates a central role for a dysregulated apoptosis in the development of SLE. In this review we will concentrate on pathogenetic concepts of autoimmune diseases as exemplified by RA and SLE.

B cell diversity and longevity in systemic autoimmunity

Despite much investigation, the nature of the primary disturbances that culminate in the production of pathogenic autoantibodies remains imprecise. However, major advances in the understanding of the genetics, the cellular and the molecular basis of pathogenic autoreactivity have been achieved in recent years. Not only B cells play a paramount role in systemic autoimmunity, but their role is not limited to secretion of autoantibodies. Under certain experimental conditions, B cells can activate memory T cells, and can process and present self-antigens to naive T cells, implying the existence of an antibody-independent mechanism for tissue injury in systemic autoimmune diseases, such as lupus. In both the mouse and the human disease, B cells secreting autoantibodies exhibit features which suggest that they are selected by specific autoantigens. Factors, such as BAFF, that support differentiation of selected B cells into mature long-lived B cells may be critical in generating deleterious autoimmune responses, at least in experimental animals. During these selection processes, the amount of signals received by the B cells are fine-tuned for optimal transmission, and kinases and phosphatases control most activities. Since a tight regulation of signaling pathways is required to prevent overt autoimmunity, faulty cell signaling may cause or exacerbate disorders of the immune system. Several observations showing altered expression of signaling molecules in T and B lymphocytes from patients with human lupus suggest that the subversion of immune receptor signaling could account for the hyperproduction of autoantibodies.

Importance of CpG dinucleotides in activation of natural IFN-alpha-producing cells by a lupus-related oligodeoxynucleotide

The oligodeoxyribonucleotide (ODN) 5'-TTTTCAATTCGAAGATGAAT-3' (ODN H), identified in systemic lupus erythematosus (SLE) serum, induced the production of interferon (IFN)-alpha in human peripheral blood mononuclear cells (PBMC) when combined with lipofectin. Flow cytometric analysis with staining for surface antigens and intracellular IFN-alpha, showed that the IFN-alpha-producing cells (IPC) were the natural IPC, also termed type 2 dendritic cell precursors (pDC2) or plasmacytoid monocytes. The importance of unmethylated CpG dinucleotides for the interferogenic activity of ODN was studied. Methylation of CpG impaired the activity of single-stranded (ss) ODN H, but increased that of the complementary ssODN I. Furthermore, CpG-methylated double-stranded (ds) ODN Hmet-Imet lost, but hemimethylated dsODN H-Imet retained interferogenic activity. Inversion of the CpG to GpC had no effect on the interferogenic activity of ssODN H, increased that of ssODN I, however abolished the activity of dsODN H-I. Alteration of the CpG in ODN H to ApG and in the ODN I to CpT destroyed their activity. The induction of IFN-alpha is therefore sequence-specific, but unmethylated CpGs are not always required, especially not in ssODNs. Interferogenic DNA sequences could therefore be more frequent in eukaryotic genomes than previously thought and their capacity to activate natural IPC may have implications for immune responses to microbial antigens and nuclear autoantigens.

From bugs to drugs: therapeutic immunomodulation with oligodeoxynucleotides containing CpG sequences from bacterial DNA

Several types of immune cells possess pattern recognition receptors (PRR) that can distinguish prokaryotic DNA from vertebrate DNA by detecting unmethylated CpG dinucleotides in particular base contexts (CpG motifs). Bacterial DNA or synthetic oligodeoxynucleotides containing these CpG motifs activate both innate and acquired immune responses that have evolved to protect against intracellular infections. These T helper 1 (Th1)-like immune responses include activation of B cells, dendritic cells, macrophages, and natural killer (NK) cells. CpG DNA-induced immune activation can protect against infection either alone or in combination with a vaccine and is effective in the immunotherapy of allergic diseases and cancer. Human clinical trials using such CpG DNA are currently underway.

Immune effects and mechanisms of action of CpG motifs

Bacterial DNA differs from vertebrate DNA in having a much higher content of unmethylated CpG dinucleotides, in particular, base contexts that are termed 'CpG motifs'. The vertebrate immune system appears to have evolved pattern recognition molecules that recognize 'CpG motifs' as foreign, and trigger protective immune responses which are strongly Th1-biased. These responses can be mimicked using synthetic oligodeoxyribonucleotides, which have demonstrated remarkable utility as vaccine adjuvants and as immunotherapeutics for treatment of cancer and allergic diseases.

Unmethylated oligo-DNA containing CpG motifs aggravates collagen-induced arthritis in mice

OBJECTIVE

To investigate the effects of an intradermal injection of an unmethylated oligodeoxynucleotide (ODN) containing CpG motifs on the severity of collagen-induced arthritis (CIA).

METHODS

CIA was induced in DBA/1 LacJ mice by immunization with bovine type II collagen (CII) in Freund's complete adjuvant followed 3 weeks later by immunization with CII in Freund's incomplete adjuvant (yielding CIA mice). Unmethylated ODN containing a CpG motif was injected intradermally into DBA/1 LacJ mice at a dosage of 20 microg (yielding CpG-CIA mice) 1 week prior to the first immunization with CII. Unmethylated ODN containing a GpC motif instead of a CpG motif and ODN containing a methylated CpG motif were used to produce controls (GpC-CIA mice and mCpG-CIA mice, respectively). After the second immunization with CII, arthritis scores were measured weekly up to the eighth week. At the eighth week, the mice were killed, histopathologic changes in the ankle joints were examined, and titers of interferon-gamma (IFNgamma) in the supernatants of splenocytes (1 x 10(7)) stimulated in culture by CII for 3 days were determined by enzyme-linked immunosorbent assay.

RESULTS

CpG-CIA mice had significantly higher arthritis scores than CIA mice. CpG-CIA mice had more severe histopathologic changes than CIA mice and mCpG-CIA mice. Moreover, splenocytes in CpG-CIA mice produced higher IFNgamma titers in response to CII than did splenocytes in CIA mice and mCpG-CIA mice.

CONCLUSION

Injection of unmethylated oligo-DNA containing CpG motifs aggravated CIA through activation of the Th1-type immune response, suggesting that microbial infection could be one of the mechanisms for aggravation or exacerbation of arthritis or, alternatively, that such infection could be an adjuvant in the induction of arthritis in rheumatoid arthritis.

Complexes of serum amyloid P component and DNA in serum from healthy individuals and systemic lupus erythematosus patients

Serum amyloid P component (SAP) binds in vitro to DNA; based on findings in SAP-deficient mice it was proposed that SAP's role is to handle chromatin and DNA, thereby preventing formation of anti-DNA antibodies. For the first time we have shown the presence of Ca2+-dependent SAP-DNA complexes, measured by ELISA, in sera from both healthy volunteers and systemic lupus erythematosus patients (SLE). The concentration of SAP-DNA complexes in SLE sera was significantly lower than in normal sera and particularly low in sera from patients with anti-DNA titers exceeding 50. The complexes were dissociated by the SAP ligand heparin and were not demonstrable in EDTA plasma. Normal sera showed similar capacity to form SAP-DNA complexes with both thymus and Escherichia coli DNA, whereas significantly lower amounts of complexes, in particular with E. coli DNA, were formed in SLE sera. SLE patients with moderate to high anti-DNA titers showed a significant negative correlation between serum SAP's binding of E. coli DNA and the anti-DNA titer.

The combination of apoptotic U937 cells and lupus IgG is a potent IFN-alpha inducer

Patients with active systemic lupus erythematosus (SLE) have signs of an ongoing IFN-alpha production, that may be of pathogenic significance in the disease. We previously showed that SLE patients have an IFN-alpha-inducing factor in blood, probably consisting of complexes containing anti-DNA Abs and immunostimulatory DNA. The DNA component could be derived from apoptotic cells, because SLE patients have been reported to have both increased apoptosis and reduced clearance of apoptotic cell material. In the present study, we therefore investigated whether apoptotic cells, together with IgG from SLE patients, could act as an IFN-alpha inducer in normal PBMC in vitro. We found that apoptotic cells of the myeloid leukemia cell line U937 as well as four other cell lines (MonoMac6, H9, Jurkat, U266) could induce IFN-alpha production in PBMC when combined with IgG from SLE patients. The IFN-alpha production by PBMC was much enhanced when PBMC were costimulated by IFN-alpha2b. The ability of IgG from different SLE patients to promote IFN-alpha induction by apoptotic U937 cells was associated with the presence of anti-ribonucleoprotein Abs, but not clearly with occurrence of anti-DNA Abs. These results suggest that apoptotic cells in the presence of autoantibodies can cause production of a clearly immunostimulatory cytokine, which is IFN-alpha. This mechanism for induction of IFN-alpha production could well be operative also in vivo, explain the IFN-alpha production seen in SLE patients, and be important in the pathogenesis of SLE.

DNA vaccines: immunology, application, and optimization*

The development and widespread use of vaccines against infectious agents have been a great triumph of medical science. One reason for the success of currently available vaccines is that they are capable of inducing long-lived antibody responses, which are the principal agents of immune protection against most viruses and bacteria. Despite these successes, vaccination against intracellular organisms that require cell-mediated immunity, such as the agents of tuberculosis, malaria, leishmaniasis, and human immunodeficiency virus infection, are either not available or not uniformly effective. Owing to the substantial morbidity and mortality associated with these diseases worldwide, an understanding of the mechanisms involved in generating long-lived cellular immune responses has tremendous practical importance. For these reasons, a new form of vaccination, using DNA that contains the gene for the antigen of interest, is under intensive investigation, because it can engender both humoral and cellular immune responses. This review focuses on the mechanisms by which DNA vaccines elicit immune responses. In addition, a list of potential applications in a variety of preclinical models is provided.

Beyond danger: unmethylated CpG dinucleotides and the immunopathogenesis of disease

Oligonucleotide sequences containing unmethylated cytidine phosphate guanosine (CpG) motifs are known to have significant immunostimulatory properties. Because of these immunostimulatory effects, unmethylated CpG oligonucleotides are thought to act as 'danger signals' that produce a favorable immune response by alerting the host to the presence of invading organisms or abnormal cells. In contrast to this concept, we review the evidence that unmethylated CpG sequences derived either from microbial agents or from endogenous CpG-rich Alu motifs promote disease progression by inducing an aberrant or autoreactive immune response. Recognition of the negative effect of unmethylated CpG dinucleotides should lead to more effective immune strategies to combat infectious, inflammatory, autoimmune and malignant diseases.

Regulation of murine airway eosinophilia and Th2 cells by antigen-conjugated CpG oligodeoxynucleotides as a novel antigen-specific immunomodulator

The characteristic features of bronchial asthma reflect the orchestrated activity of Th2 cells. Oligodeoxynucleotides containing CpG motifs (CpG) have recently been highlighted as an immunomodulator that biases toward a Th1-dominant phenotype. We have previously reported that intratracheal coadministration of CpG and allergen inhibited airway eosinophilia and hyperresponsiveness in a synergistic manner. To substantiate the synergism between CpG and Ag, we introduced a covalently linked conjugate between CpG and Ag and examined the efficacy on airway eosinophilia and Th2 cytokine production. We found that the conjugated form of CpG plus Ag was 100-fold more efficient in regulating airway eosinophilia than the unconjugated mixture. The inhibitory effects lasted for at least 2 mo. The inhibition of airway eosinophilia by the conjugate was Ag specific and associated with an improvement of the airway hyperresponsiveness and the unresponsiveness of the Ag-specific Th2 cells in the regional lymph nodes. The CpG-Ag conjugate was 100-fold more effective than the unconjugated mixture for inducing in vitro Th1 differentiation in an IL-12-dependent manner. Our data show that CpG conjugated to Ag can work as a novel Ag-specific immunomodulator and imply that inhalation of allergen-CpG conjugate could be a desensitization therapy for patients with bronchial asthma.

A combination of poloxamers increases gene expression of plasmid DNA in skeletal muscle

Intramuscular administration of plasmid DNA is a promising strategy to express therapeutic genes, however, it is limited by a relatively low level of gene expression. We report here that a non-ionic carrier, SP1017, composed of two amphiphilic block copolymers, pluronics L61 and F127, also known as poloxamers, significantly increases intramuscular expression of plasmid DNA. Two reporter genes, luciferase and beta-galactosidase, and one therapeutic gene, erythropoietin, were injected intramuscularly with and without SP1017 into C57Bl/6 and Balb/C mice and Sprague-Dawley rats. SP1017 increased gene expression by about 10-fold and maintained higher gene expression compared with naked DNA. Comparison of SP1017 with polyvinyl pyrrolidone (PVP) showed that SP1017 exhibited a significantly higher efficacy and its optimal dose was 500-fold lower. Experiments with beta-galactosidase using X-gal staining suggested that SP1017 considerably increased plasmid DNA diffusion through the tissue. SP1017 also improved expression of the erythropoietin gene leading to an increase in its systemic level and hematocrits. Previous toxicity studies have suggested that SP1017 has over a 1000-fold safety margin. Poloxamers used in SP1017 are listed in the US Pharmacopeia as inactive excipients and are widely used in a variety of clinical applications. We believe that the described system constitutes a simple and efficient gene transfer method to achieve local or systemic production of therapeutic proteins.

Responses of human B cells to DNA and phosphorothioate oligodeoxynucleotides

Emerging information has documented that certain DNA and sODNs can be both immunogenic and immunostimulatory. sODNs, but not DNA, induce T-cell-independent polyclonal activation of human B cells by engaging cell-surface receptors. Manifestations of sODN-induced human B-cell activation include expression of activation markers, proliferation, Ig production and anti-DNA antibody production. IL-2 and intact T cells enhanced B-cell responses to sODNs but were not required. Monocytes also provided a modest enhancement of human B-cell responses induced by sODNs. The chemical nature of sODNs capable of stimulating human B cells and the specific cell-surface receptors involved have not been completely delineated. Further studies will be necessary to elucidate the potential role of stimulatory sODNs in disease pathogenesis and to develop a means to employ ODNs as therapeutic agents in humans.

Regulation of T-helper type 2 cell and airway eosinophilia by transmucosal coadministration of antigen and oligodeoxynucleotides containing CpG motifs

The characteristic features of bronchial asthma, including airway eosinophilia and elevated immunoglobulin (Ig)E levels, are known to be orchestrated by T-helper (Th) 2 cells. Oligodeoxynucleotides containing CpG motifs (CpG) have recently been highlighted as an immunomodulator that biases toward a Th1-dominant phenotype. However, CpG may incur nonspecific Th1 activation and toxic effects. In this study we report a novel inhibition of Th2 cells by transmucosal inoculation of antigen and CpG. Intratracheal instillation of CpG inhibited airway eosinophilia and Th2 cytokine production in antigen-sensitized mice. The inhibition was observed when CpG was given at the same time or in advance of antigen challenge. Notably, concomitant administration of CpG and antigen (as opposed to either one alone) was essential for the inhibitory effects. The antigen dose could be minimized to avoid a harmful boost of eosinophilia. CpG had few effects on systemic anti-ovalbumin IgE responses. These results demonstrate that a synergism between transmucosally administered allergen and CpG inhibits Th2 cells in parallel with an improvement in airway eosinophilia and hyperresponsiveness without impeding systemic immune responses. Our data imply that inhalation of a minimal amount of allergen plus CpG could be a novel desensitization therapy for patients with bronchial asthma.

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.

CpG DNA rescues B cells from apoptosis by activating NFkappaB and preventing mitochondrial membrane potential disruption via a chloroquine-sensitive pathway

Isolated murine splenic B cells gradually undergo spontaneous apoptosis while WEHI-231 B lymphoma cells undergo activation-induced apoptosis. Unmethylated CpG dinucleotides in a particular sequence context (CpG motif) in bacterial DNA or in synthetic oligodeoxynucleotides (CpG DNA) rescue both splenic B cells and WEHI-231 cells from apoptosis, an effect which could potentially contribute to autoimmune disease. Chloroquine has been used as an effective therapeutic agent for some autoimmune diseases, although the mechanism of action is not clearly understood. Low concentrations of chloroquine (<5 microM) selectively abolished CpG DNA-mediated protection against spontaneous apoptosis of splenic B cells and against anti-IgM-induced apoptosis of WEHI-231 cells without affecting anti-apoptotic activities of anti-CD40 or lipopolsaccharide. CpG DNA effectively prevented mitochondrial membrane potential disruption through a chloroquine-sensitive pathway in splenic B cells. Apoptosis protection by CpG DNA was also associated with increased expression of several proto-oncogenes and oncoproteins directly and/or indirectly through a rapid and sustained activation of NFkappaB in splenic B cells and WEHI-231 cells. These effects were also suppressed by chloroquine. Our results suggest that despite the difference in maturation phenotype of splenic B cells and WEHI-231 cells, CpG DNA rescues both from apoptosis by similar pathway, which is blocked at an early step by chloroquine.

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.

The Role of Environmental Antigens in the Spontaneous Development of Autoimmunity in MRL-lpr Mice

It has been proposed that the “normal” stimulation of the immune system that occurs from interactions with environmental stimuli, whether infectious or dietary, is necessary for the initiation and/or continuation of autoimmunity. We tested this hypothesis by deriving a group of MRL-lpr mice into a germfree (GF) environment. At 5 mo of age, no differences between GF and conventional MRL-lpr mice were noted in lymphoproliferation, flow cytometric analysis of lymph node cells (LN), or histologic analysis of the kidneys. Autoantibody levels were comparably elevated in both groups. A second experiment tested the role of residual environmental stimuli by contrasting GF mice fed either a low m.w., ultrafiltered Ag-free (GF-AF) diet or an autoclaved natural ingredient diet (GF-NI). At 4 mo of age, both groups showed extensive lymphoproliferation and aberrant T cell formation, although the GF-AF mice had ∼50% smaller LNs compared with sex-matched GF-NI controls. Autoantibody formation was present in both groups. Histologic analysis of the kidneys revealed that GF-AF mice had much lower levels of nephritis, while immunofluorescence analysis demonstrated no difference in Ig deposits but did reveal a paucity of C3 deposition in the kidneys of GF-AF mice.

These data do not support a role for infectious agents in the induction of lymphoproliferation and B cell autoimmunity in MRL-lpr mice. Furthermore, they suggest that autoantibodies do not originate from B cells that were initially committed to exogenous Ags. They do suggest a possible contributory role for dietary exposure in the extent of lymphoproliferation and development of nephritis in this strain.

RNAs in the sera of Persian Gulf War veterans have segments homologous to chromosome 22q11.2

Reverse transcriptase PCR (RT-PCR) was used for polyribonucleotide assays with sera from deployed Persian Gulf War veterans with the Gulf War Syndrome and a cohort of nonmilitary controls. Sera from veterans contained polyribonucleotides (amplicons) that were obtained by RT-PCR and that ranged in size from 200 to ca. 2,000 bp. Sera from controls did not contain amplicons larger than 450 bp. DNA sequences were derived from two amplicons unique to veterans. These amplicons, which were 414 and 759 nucleotides, were unrelated to each other or to any sequence in gene bank databases. The amplicons contained short segments that were homologous to regions of chromosome 22q11.2, an antigen-responsive hot spot for genetic rearrangements. Many of these short amplicon segments occurred near, between, or in chromosome 22q11.2 Alu sequences. These results suggest that genetic alterations in the 22q11.2 region, possibly induced by exposures to environmental genotoxins during the Persian Gulf War, may have played a role in the pathogenesis of the Gulf War Syndrome. However, the data did not exclude the possibility that other chromosomes also may have been involved. Nonetheless, the detection of polyribonucleotides such as those reported here may have application to the laboratory diagnosis of chronic diseases that have a multifactorial etiology.

Patients with systemic lupus erythematosus (SLE) have a circulating inducer of interferon-alpha (IFN-alpha) production acting on leucocytes resembling immature dendritic cells

Patients with active SLE often have an ongoing production of IFN-alpha. We therefore searched for an endogenous IFN-alpha-inducing factor (IIF) in SLE patients and found that their sera frequently induced production of IFN-alpha in cultures of peripheral blood mononuclear cells (PBMC) from healthy blood donors, especially when the PBMC were costimulated with the cytokines IFN-alpha2b and granulocyte-macrophage colony-stimulating factor (GM-CSF). The phenotype of the IFN-alpha-producing cells (IPC) as determined by flow cytometry corresponded to that of the natural IPC, resembling immature dendritic cells. The IIF activity in SLE sera was sometimes as high as that of a virus and was present especially in patients with active disease and with measurable IFN-alpha levels in serum. The IIF had an apparent molecular weight of 300-1000 kD and appeared to consist of both immunoglobulin and DNA, possibly being immune complexes. This endogenous IFN-alpha inducer may be of pathogenic significance, since a reported occasional adverse effect of IFN-alpha therapy in patients with non-autoimmune disorders is development of anti-dsDNA antibodies and SLE.

Activation of macrophages and B lymphocytes by an oligodeoxynucleotide derived from an acutely pathogenic simian immunodeficiency virus

Certain CpG-containing DNA sequences from bacteria, viruses, or invertebrates elicit responses in the vertebrate innate immune system. These responses also account for many nonspecific effects of oligodeoxynucleotides used for antisense approaches. Here we describe a sequence from an acutely pathogenic simian immunodeficiency virus (SIV) that induces release of cytokines from macrophages and B lymphocyte proliferation. Furthermore, several similar sequences in other immunodeficiency viruses were found that also activate macrophages. These results led to the question if CpG-containing DNA, which is thought to play an immunostimulatory role in bacterial infections, has a similar role in infections by immunodeficiency viruses.

Impaired phagocytosis of apoptotic cell material by monocyte-derived macrophages from patients with systemic lupus erythematosus

OBJECTIVE

To investigate whether the established impaired phagocyte function in systemic lupus erythematosus (SLE) patients also affects apoptotic cell clearance. Accumulation of apoptotic waste as a source for autoantigens that induce and maintain autoimmune responses is discussed.

METHODS

Apoptosis was detected by morphology and propidium iodide staining. In vitro phagocytosis of autologous apoptotic cells in cultured peripheral blood mononuclear cells was evaluated microscopically. Cross-feeding experiments were performed to investigate phagocytosis of heterologous apoptotic cells by in vitro-differentiated macrophages. Furthermore, the effect of annexin V on the phagocytosis of apoptotic cells was investigated.

RESULTS

Reduced clearance of apoptotic cells in SLE patients was observed. The defective clearance appeared to reflect phagocyte dysfunction and not an abnormal execution of apoptosis. A similar picture was seen when in vitro-differentiated macrophages from control populations were treated with annexin V.

CONCLUSION

Noninflammatory engulfment phagocytosis of apoptotic cells is decreased in SLE patients. Persistently circulating apoptotic waste may encounter inflammatory removal pathways and serve as immunogen for the induction of autoreactive lymphocytes and as antigen for immune complex formation.

DNA as an adjuvant: capacity of insect DNA and synthetic oligodeoxynucleotides to augment T cell responses to specific antigen

How strong adjuvants such as complete Freund's adjuvant (CFA) promote T cell priming to protein antigens in vivo is still unclear. Since the unmethylated CpG motifs in DNA of bacteria and other nonvertebrates are stimulatory for B cells and antigen-presenting cells, the strong adjuvanticity of CFA could be attributed, at least in part, to the presence of dead bacteria, i.e., a source of stimulatory DNA. In support of this possibility, evidence is presented that insect DNA in mineral oil has even stronger adjuvant activity than CFA by a number of parameters. Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs mimic the effects of insect DNA and, even in soluble form, ODNs markedly potentiate clonal expansion of T cell receptor transgenic T cells responding to specific peptide.

Antagonism of Immunostimulatory CpG-Oligodeoxynucleotides by Quinacrine, Chloroquine, and Structurally Related Compounds

Phosphorothioate oligodeoxynucleotides containing CpG (CpG-ODN) activate immune responses. We report that quinacrine, chloroquine, and structurally related compounds completely inhibit the antiapoptotic effect of CpG-ODN on WEHI 231 murine B lymphoma cells and inhibit CpG-ODN-induced secretion of IL-6 by WEHI 231. They also inhibit IL-6 synthesis and thymidine uptake by human unfractionated PBMC induced by CpG-ODN. The compounds did not inhibit LPS-induced responses. Half-maximal inhibition required 10 nM quinacrine or 100 nM chloroquine. Inhibition was noncompetitive with respect to CpG-ODN. Quinine, quinidine, and primaquine were much less powerful. Quinacrine was effective even when added after the CpG-ODN. Near-toxic concentrations of ammonia plus bafilomycin A1 (used to inhibit vesicular acidification) did not reduce the efficacy of the quinacrine, but the effects of both quinacrine and chloroquine were enhanced by inhibition of the multidrug resistance efflux pump by verapamil. Agents that bind to DNA, including propidium iodide, Hoechst dye 33258, and coralyne chloride did not inhibit CpG-ODN effect, nor did 4-bromophenacyl bromide, an inhibitor of phospholipase A2. Examination of the structure-activity relationship of seventy 4-aminoquinoline and 9-aminoacridine analogues reveals that increased activity was conferred by bulky hydrophobic substituents on positions 2 and 6 of the quinoline nucleus. No correlation was found between published antimalarial activity and ability to block CpG-ODN-induced effects. These results are discussed in the light of the ability of quinacrine and chloroquine to induce remission of rheumatoid arthritis and lupus erythematosus.

Radiotherapy for malignancies associated with lupus: case reports of acute and late reactions

Six patients with lupus (five with systemic lupus erythematosus and one with discoid lupus) were treated with moderate-dose to high-dose standard radiation treatment for breast cancer (four patients), Hodgkin's disease (one patient), and thymoma (one patient). None of the patients had severe acute or late radiation complications in the skin or subcutaneous tissues treated, with a follow-up of 7-121 months. Systemic lupus erythematosus is not an absolute contraindication to radiotherapy, which can be offered to patients with malignant disease that can be appropriately treated with this modality.