Major peptide autoepitopes for nucleosome-specific T cells of human lupus

Regulatory T cell (Treg) subsets return in patients with refractory lupus following stem cell transplantation, and TGF-beta-producing CD8+ Treg cells are associated with immunological remission of lupus

Compared with conventional drug therapy, autologous hemopoietic stem cell transplantation (HSCT) can induce very-long-term remission in refractory lupus patients. Herein, we show that in posttransplant patients, both CD4(+)CD25(high)FoxP3(+) and an unusual CD8(+)FoxP3(+) Treg subset return to levels seen in normal subjects; accompanied by almost complete inhibition of pathogenic T cell response to critical peptide autoepitopes from histones in nucleosomes, the major lupus autoantigen from apoptotic cells. In addition to a stably sustained elevation of FoxP3, posttransplant CD8 T cells also maintained markedly higher expression levels of latency-associated peptide (LAP), CD103, PD-1, PD-L1, and CTLA-4, as compared with pretransplant CD8 T cells that were identically treated by a one-time activation and rest in short-term culture. The posttransplant CD8 regulatory T cells (Treg) have autoantigen-specific and nonspecific suppressive activity, which is contact independent and predominantly TGF-beta dependent. By contrast, the pretransplant CD8 T cells have helper activity, which is cell contact dependent. Although CD4(+)CD25(high) Treg cells return during clinical remission of conventional drug-treated lupus, the posttransplant patient's CD8 Treg cells are considerably more potent, and they are absent in drug-treated patients in whom CD4 T cell autoreactivity to nucleosomal epitopes persists even during clinical remission. Therefore, unlike conventional drug therapy, hemopoietic stem cell transplantation generates a newly differentiated population of LAP(high)CD103(high) CD8(TGF-beta) Treg cells, which repairs the Treg deficiency in human lupus to maintain patients in true immunological remission.

Defensins in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease, resulting in inflammation and tissue damage. The precise etiology for SLE is so far unknown. It has been shown that the innate immunity plays a role in SLE pathogenesis. The innate immune system confers broad protection against pathogens by the secretion of broad-spectrum antibacterial and immunomodulatory substances named defensins. Recently, alpha-defensin, the products of neutrophils have been found to be upregulated at the mRNA and protein levels in SLE patients. In addition, increased antidefensin antibodies were found in sera of patients with SLE, but these levels decreased after therapy with corticosteroids. These recent findings suggest a role for defensins in the pathogenesis of SLE. Thus, activation and degranulation of neutrophils leads to alpha-defensin secretion in SLE patients. Given their immunomodulatory role, alpha-defensin secretion might activate the adaptive immune system leading to the stimulation of the immune system, as is manifested in SLE.

The role of B cells in lupus pathogenesis

Autoantibodies clearly contribute to tissue inflammation in systemic lupus erythematosus. In order to therapeutically target B cells making pathogenic autoantibodies, it is necessary to identify their phenotype. It is also important to understand the defects in B cell repertoire selection that permit pathogenic autoreactive B cells to enter the immunocompetent B cell repertoire. We present the data that both marginal zone and follicular B cells can produce pathogenic autoantibodies. Moreover, we discuss how B cell survival and maturation are regulated centrally prior to antigen activation and in the periphery after antigen activation to form the repertoire that generates the spectrum of circulating antibodies.

High circulating levels of free interleukin-18 in patients with active SLE in the presence of elevated levels of interleukin-18 binding protein

Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies particularly to nuclear antigens and by an abnormal production of proinflammatory cytokines. In the present study, we measured the levels of the proinflammatory cytokine IL-18 and its natural inhibitor, the IL-18 binding protein (IL-18BP), in sera of SLE patients at various stages of the disease. This is the first study to present IL-18BP levels in sera of SLE patients as well as the calculated, biologically active, free IL-18 concentrations that are most probably more relevant to the pathology of SLE. Sera from 48 unselective SLE patients (total of 195 samples) were obtained longitudinally with a mean follow-up period of 11.1 +/- 8.9 years and were compared to sera from 100 healthy volunteers. Circulating levels of IL-18, IL-18BP and free IL-18 in the SLE patients were significantly higher than the levels of healthy controls (5 fold, 6 fold and 3 fold for IL-18, IL-18BP and free IL-18, respectively) and correlated with disease activity as scored by SLEDAI-2K. Furthermore, these levels during active disease (SLEDAI-2K > or = 6) were higher compared to the levels measured in the sera of the same patients during remission or during mild disease (SLEDAI-2K 0-5). The high levels of IL-18 and IL-18BP in sera of active SLE patients suggest their possible role in the pathogenesis and course of the disease. However, despite the elevated levels of IL-18BP during active disease, free IL-18 remained more than 2 fold higher than the levels in healthy controls suggesting a potential benefit of administration of exogenous IL-18BP as a novel therapeutic approach for active SLE.

High alpha-defensin levels in patients with systemic lupus erythematosus

Innate immunity plays a role in systemic lupus erythematosus (SLE). Our objective was to determine the levels of defensins, which are antimicrobial and immunomodulatory polypeptides, in SLE. Sera from SLE patients and healthy controls were tested for pro-inflammatory human beta-defensin 2 (hBD-2) and for alpha-defensin human neutrophil peptide 1 (HNP-1). hBD-2 could not be detected by enzyme-linked immunosorbent assay (ELISA) and its mRNA levels were low in SLE patients and similar to those found in controls. In contrast, the mean alpha-defensin level in the sera of all SLE patients (11.07 +/- 13.92 ng/microl) was significantly higher than that of controls (0.12 +/- 0.07 ng/microl). Moreover, 60% of patients demonstrated very high serum levels (18.5 +/- 13.36 ng/microl) and 50% showed elevated gene expression in polymorphonuclear cells. High alpha-defensin levels correlated with disease activity, but not with neutrophil count. Thus, activation and degranulation of neutrophils led to alpha-defensin secretion in SLE patients. Given the immunomodulatory role of alpha-defensins, it is possible that their secretion may activate the adaptive immune system leading to a systemic response.

Potential for anti-DNA immunoglobulin peptide therapy in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with elevated morbidity and multi-organ involvement. While many strategies have shown efficacy and improved management of SLE, they have often been associated with adverse effects. Some patients may not respond well to some treatments because of inter-individual variability of the disease. More specific and safer therapies are needed.

OBJECTIVE/METHODS

To review literature on peptide-based therapy of SLE.

RESULTS/CONCLUSIONS

Recently, emphasis has been placed on targeting molecules and pathways involved in the inflammatory response in SLE, including the use of immunogenic peptides derived from anti-DNA antibodies. Encouraging data from murine models of SLE have led to tests in initial clinical trials in humans--which have unfortunately not met the primary endpoints. The current challenge is to design improved strategies for immunotherapeutic use of anti-DNA peptides in SLE.

Apigenin, a non-mutagenic dietary flavonoid, suppresses lupus by inhibiting autoantigen presentation for expansion of autoreactive Th1 and Th17 cells

Introduction

Lupus patients need alternatives to steroids and cytotoxic drugs. We recently found that apigenin, a non-mutagenic dietary flavonoid, can sensitize recurrently activated, normal human T cells to apoptosis by inhibiting nuclear factor-kappa-B (NF-κB)-regulated Bcl-x_L, cyclooxygenase 2 (COX-2), and cellular FLICE-like inhibitory protein (c-FLIP) expression. Because sustained immune activation and hyperexpression of COX-2 and c-FLIP contribute to lupus, we treated SNF1 mice that spontaneously develop human lupus-like disease with apigenin.

Methods

SNF1 mice with established lupus-like disease were injected with 20 mg/kg of apigenin daily and then monitored for development of severe nephritis. Histopathologic changes in kidneys, IgG autoantibodies to nuclear autoantigens in serum and in cultures of splenocytes, along with nucleosome-specific T helper 1 (Th1) and Th17 responses, COX-2 expression, and apoptosis of lupus immune cells were analyzed after apigenin treatment.

Results

Apigenin in culture suppressed responses of Th1 and Th17 cells to major lupus autoantigen (nucleosomes) up to 98% and 92%, respectively, and inhibited the ability of lupus B cells to produce IgG class-switched anti-nuclear autoantibodies helped by these Th cells in presence of nucleosomes by up to 82%. Apigenin therapy of SNF1 mice with established lupus suppressed serum levels of pathogenic autoantibodies to nuclear antigens up to 97% and markedly delayed development of severe glomerulonephritis. Apigenin downregulated COX-2 expression in lupus T cells, B cells, and antigen-presenting cells (APCs) and caused their apoptosis. Autoantigen presentation and Th17-inducing cytokine production by dendritic cells were more sensitive to the inhibitory effect of apigenin in culture, as evident at 0.3 to 3 μM, compared with concentrations (10 to 100 μM) required for inducing apoptosis.

Conclusions

Apigenin inhibits autoantigen-presenting and stimulatory functions of APCs necessary for the activation and expansion of autoreactive Th1 and Th17 cells and B cells in lupus. Apigenin also causes apoptosis of hyperactive lupus APCs and T and B cells, probably by inhibiting expression of NF-κB-regulated anti-apoptotic molecules, especially COX-2 and c-FLIP, which are persistently hyperexpressed by lupus immune cells. Increasing the bioavailability of dietary plant-derived COX-2 and NF-κB inhibitors, such as apigenin, could be valuable for suppressing inflammation in lupus and other Th17-mediated diseases like rheumatoid arthritis, Crohn disease, and psoriasis and in prevention of inflammation-based tumors overexpressing COX-2 (colon, breast).

Developments in the scientific understanding of lupus

Systemic lupus erythematosus is a systemic autoimmune disease characterized by the production of antinuclear antibodies (ANAs). Recent research into human and murine lupus suggests that disease susceptibility results from genetic polymorphisms regulating immune responses as well as impairing the clearance of apoptotic cells. Because the products of dead cells, including nucleic acids, have immunologic activity, this situation can promote antigen-driven ANA responses. Furthermore, immune complexes of ANAs can drive the production of proinflammatory cytokines, inducing the 'interferon signature', and intensifying disease. Together, these findings point to new genetic and immunologic markers of disease as well as targets for new therapies.

Induction of immune tolerance by activation of CD8+ T suppressor/regulatory cells in lupus-prone mice

Multiple CD8(+) suppressive T cell (Ts) subtypes are now recognized as essential regulators of the immune system that prevent autoimmunity through secretion of multiple cytokines and the subsequent inhibition of effector lymphocyte function. CD8(+) Ts are an exciting area of study because of the possible therapeutic implications of inducing suppressive cells that are able to subdue or anergize autoimmune manifestations. Current research in systemic lupus erythematosus (SLE), a disease in which most effective therapies are widely immunosuppressive, is often focused on novel and highly targeted ways in which to treat this multiorgan disease. CD8(+) Ts have been impaired in human and murine SLE. Our group and others have utilized tolerogenic peptides to induce and study CD8(+) Ts to understand their function, as well as investigate a possible new SLE therapy. This review will discuss the similarities and differences in CD8(+) Ts subsets, the concept of tolerance as a therapy, and the current understanding of CD8(+) Ts in mouse SLE models.

Analysis of the interindividual conservation of T cell receptor alpha- and beta-chain variable regions gene in the peripheral blood of patients with systemic lupus erythematosus

The aim of this study was to find conserved motifs in specific T cell receptor (TCR) alpha- and beta-chains, and to analyse the association between complementarity determining region 3 (CDR3) spectratype and systemic lupus erythematosus (SLE) activity. TCR alpha-and beta-chain CDR3 spectratypes were analysed in 20 SLE patients. The CDR3 spectratypes of three patients were monitored over time, and the CDR3 regions of clonally expanded T cells were sequenced. CDR3 spectratype analysis showed prominent usage of TCR AV8, AV14, AV23, AV30, AV31, BV2, BV8, BV11, BV14, BV16, BV19 and BV24 families in SLE patients. The CDR3 spectratype showed dynamic change correlating with SLE activity. The sequence of the CDR3 region in clonally expanded T cells suggested a conserved GGX amino acid motif in both alpha- and beta-chains. The Ja34 and Jb2s1 region genes were found in high frequency. Both TCR Valpha and Vbeta gene usage is highly restricted in SLE, suggesting that the TCRs recognize a limited number of antigenic epitopes. The conserved motifs and limited use of joining region genes may indicate the recognition of similar antigenic epitopes in multiple individuals.

Pathogenic anti-nucleosome antibodies

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

Natural regulatory T cells: number and function are normal in the majority of patients with lupus nephritis

CD4(+) CD25(+) regulatory T cells have been shown to be a vital component of the mechanisms that prevent autoreactivity in mice and also in humans. Previous studies have examined CD4(+) CD25(hi) regulatory T cell frequency and function in patients with systemic lupus erythematosus (SLE) with mixed results. We investigated frequency, phenotype and function in 21 patients with SLE and six with inactive disease. We found no reduction in frequency of the CD25(hi) subset, although active disease was associated with an increased proportion of CD4(+) CD25(+) T cells. When examining function, in the majority of individuals suppression was comparable with controls, although cells isolated from one patient with active disease failed to suppress proliferation. On testing the effect of CD25(hi) depletion on the responses of whole peripheral blood mononuclear cells to nucleosomes we found that, where a response was detectable from patients, depletion augmented interferon-gamma secretion, demonstrating intact suppression of responses implicated in the pathogenesis of SLE. Our results did not confirm an association of failure in CD4(+) CD25(hi) regulatory T cell function or a reduction in their frequency with active disease. Instead, perturbations in the CD4(+) CD25(hi) regulatory T cell population may play a role in disease in only a minority of the patients afflicted by the diverse syndromes of SLE.

Toll-like receptors and innate immune responses in systemic lupus erythematosus

A series of discoveries over the past several years has provided a new paradigm for understanding autoimmunity in systemic lupus erythematosus. The discoveries of pattern recognition receptors and of how these receptors can be recruited into autoimmune responses underpin this paradigm. The implications of these observations continue to unfold with ongoing investigation into the range and specificity of pattern recognition receptors, into how immune complexes containing nucleic acids trigger these receptors, into how endogenous macromolecular 'danger signals' stimulate innate immune responses, and into the effect of pattern recognition receptor activation on various cell types in initiating and perpetuating autoimmunity. The development of clinical trials using therapeutic agents that target components of the innate immune system suggests that these advances may soon culminate in new medications for treating patients with systemic lupus erythematosus.

Low-dose peptide tolerance therapy of lupus generates plasmacytoid dendritic cells that cause expansion of autoantigen-specific regulatory T cells and contraction of inflammatory Th17 cells

Subnanomolar doses of an unaltered, naturally occurring nucleosomal histone peptide epitope, H4(71-94), when injected s.c. into lupus-prone mice, markedly prolong lifespan by generating CD4+25+ and CD8+ regulatory T cells (Treg) producing TGF-beta. The induced Treg cells suppress nuclear autoantigen-specific Th and B cells and block renal inflammation. Splenic dendritic cells (DC) captured the s.c.-injected H4(71-94) peptide rapidly and expressed a tolerogenic phenotype. The DC of the tolerized animal, especially plasmacytoid DC, produced increased amounts of TGF-beta, but diminished IL-6 on stimulation via the TLR-9 pathway by nucleosome autoantigen and other ligands; and those plasmacytoid DC blocked lupus autoimmune disease by simultaneously inducing autoantigen-specific Treg and suppressing inflammatory Th17 cells that infiltrated the kidneys of untreated lupus mice. Low-dose tolerance with H4(71-94) was effective even though the lupus immune system is spontaneously preprimed to react to the autoepitope. Thus, H4(71-94) peptide tolerance therapy that preferentially targets pathogenic autoimmune cells could spare lupus patients from chronically receiving toxic agents or global immunosuppressants and maintain remission by restoring autoantigen-specific Treg cells.

Apoptosis-induced acetylation of histones is pathogenic in systemic lupus erythematosus

OBJECTIVE

In systemic lupus erythematosus (SLE), inadequate removal of apoptotic cells may lead to challenge of the immune system with immunogenic self antigens that have been modified during apoptosis. We undertook this study to evaluate whether apoptosis-induced histone modifications are targets for the immune system in SLE.

METHODS

The epitope of KM-2, a monoclonal antihistone autoantibody derived from a lupus mouse, was mapped by random peptide phage display. The reactivity of KM-2 and plasma with (acetylated) histone H4 (H4) peptides and with nonapoptotic, apoptotic, and hyperacetylated histones was determined by immunofluorescence staining, enzyme-linked immunosorbent assay, and Western blotting.

RESULTS

KM-2 recognized apoptosis-induced acetylation of H4 at lysines 8, 12, and 16. The majority of plasma samples from SLE patients and lupus mice showed higher reactivity with triacetylated H4 peptide (residues 1-22) and with hyperacetylated and apoptotic histones than with nonacetylated H4 peptide and normal histones. Importantly, administration of triacetylated H4 peptide to lupus-prone mice before disease onset accelerated the disease by enhancing mortality and aggravating proteinuria, skin lesions, and glomerular IgG deposition, while the nonacetylated H4 peptide had no pathogenic effect. The delayed-type hypersensitivity response in lupus mice against the triacetylated H4 peptide was higher than that against the nonacetylated H4 peptide. Bone marrow-derived dendritic cells (DCs) cultured in the presence of hyperacetylated nucleosomes showed increased expression/production of CD40, CD86, interleukin-6 (IL-6), and tumor necrosis factor alpha compared with DCs cultured in the presence of normal nucleosomes. Finally, DCs cultured in the presence of hyperacetylated nucleosomes were able to activate syngeneic T cells, because IL-2 production increased.

CONCLUSION

Apoptosis-induced acetylation of nucleosomes may represent an important driving force in the development of lupus.

Physiopathologie du lupus érythémateux systémique

Innate immunity is directly implicated in the pathophysiology of lupus through the dendritic cell system and the activation by immune complexes of some toll-like receptors (TLR). Interferon-alpha plays a key role in the pathophysiology of lupus and represents a promising target for immune therapy. Dendritic cells are activated and able to capture large quantities of nuclear antigen-containing bodies to stimulate specific adaptive immune response.

TLR2/TLR4-independent neutrophil activation and recruitment upon endocytosis of nucleosomes reveals a new pathway of innate immunity in systemic lupus erythematosus

The nucleosome is a major autoantigen in systemic lupus erythematosus (SLE); it can be detected as a circulating complex in the serum, and nucleosomes have been suggested to play a key role in disease development. In the present study, we show for the first time that physiological concentrations of purified nucleosomes trigger innate immunity. The nucleosomes are endocytosed and induce the direct activation of human neutrophils (polymorphonuclear leukocytes (PMN)) as revealed by CD11b/CD66b up-regulation, IL-8 secretion, and increased phagocytic activity. IL-8 is a neutrophil chemoattractant detected in high concentrations in the sera of patients, and IL-8 secretion might thus result in enhanced inflammation, as observed in lupus patients, via an amplification loop. Nucleosomes act as free complexes requiring no immune complex formation and independently of the presence of unmethylated CpG DNA motifs. Both normal and lupus neutrophils are sensitive to nucleosome-induced activation, and activation is not due to endotoxin or high-mobility group box 1 contamination. In mice, i.p. injection of purified nucleosomes induces neutrophil activation and recruitment in a TLR2/TLR4-independent manner. Importantly, neutrophils have been suggested to link innate and adaptive immunity. Thus, nucleosomes trigger a previously unknown pathway of innate immunity, which may partially explain why peripheral tolerance is broken in SLE patients.

Pathogenic role of anti-C1q autoantibodies in the development of lupus nephritis—a hypothesis

A substantial proportion of patients with systemic lupus erythematosus (SLE) develop renal inflammatory disease, so-called lupus nephritis (LN). LN is a severe complication of SLE which is strongly associated with the presence of autoantibodies against C1q, the first component of the complement system, and other self-antigens (i.e. against DNA and nucleosomes) as well. In this review, the authors focus on anti-C1q autoantibodies and interpret the available data in order to explain how LN may develop and how anti-C1q autoantibodies contribute to its pathogenesis.

Regulatory T cells in lupus

Naturally occurring, CD4+ CD25+ regulatory T cells that are exported from the thymus early in life play an important role in controlling organ-specific autoimmune diseases, but they may not be critical for suppressing systemic autoimmunity in lupus. On the other hand, lupus-prone subjects appear to be deficient in generation of adaptive T-regulatory cells that can be induced by various means. We review autoantigen-specific therapeutic approaches that induce such regulatory T cells. Of particular interest are TGF-ss producing CD4+ CD25+ and CD8+ regulatory T cells that are induced by low dose tolerance therapy of lupus-prone mice with nucleosomal histone peptide epitopes, administered subcutaneously in subnanomolar doses. These regulatory T cells are not only efficient in suppressing autoantigen recognition and autoantibody production, but they also inhibit migration/accumulation of pathogenic autoimmune cells in the target organ, such as the kidneys of mice prone to develop lupus nephritis. We discuss why and under what conditions such therapeutic approaches would be beneficial in lupus patients and lupus-prone subjects.

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.

Systemic lupus erythematosus—2005 annus mirabilis?

We are about to enter a new era in the treatment of patients with systemic lupus erythematosus (SLE). For the past 40 years hydroxychloroquine sulfate and corticosteroids, together with varying combinations of immunosuppressive drugs, have been the main treatments for SLE. Although effective for many patients, some patients fail to respond to these drugs and even more suffer from major side effects due to the generalized nature of the immunosuppression. In this article we review the remarkable confluence of new therapies ranging from newer immunosuppressive drugs with fewer side effects, such as mycophenolate mofetil, to the more targeted approaches offered by biological agents. These agents have been designed to block molecules such as CD20, CD22 and interleukin-10 that are thought to have an integral part in the development of SLE. This wolf might not yet be about to become extinct but its survival is increasingly under threat!

Selective modulation of CD4+ T cells from lupus patients by a promiscuous, protective peptide analog

A peptide encompassing residues 131-151 of the spliceosomal U1-70K protein and its analog phosphorylated at Ser140 were synthesized as potential candidates for the treatment of patients with lupus. Studies in the MRL/lpr and (NZB x NZW)F1 lupus models have demonstrated that these sequences contain a CD4+ T cell epitope but administration of the phosphorylated peptide only ameliorates the clinical manifestations of treated MRL/lpr mice. Binding assays with soluble HLA class II molecules and molecular modeling experiments indicate that both peptides behave as promiscuous epitopes and bind to a large panel of human DR molecules. In contrast to normal T cells and T cells from non-lupus autoimmune patients, we found that PBMCs from 40% of lupus patients selected randomly and CFSE-labeled CD4+ T cells proliferate in response to peptide 131-151. Remarkably, however, we observed that phosphorylation of Ser140 prevents CD4+ T cells proliferation but not secretion of regulatory cytokines, suggesting a striking immunomodulatory effect of phosphorylated analog on lupus CD4+ T cells that was unique to patients. The analog might act as an activator of regulatory T cells or as a partial agonist of TCR.

A Defect in Deletion of Nucleosome-Specific Autoimmune T Cells in Lupus-Prone Thymus: Role of Thymic Dendritic Cells

To study central tolerance to the major product of ongoing apoptosis in the thymus, we made new lines of transgenic (Tg) mice expressing TCR of a pathogenic autoantibody-inducing Th cell that was specific for nucleosomes and its histone peptide H4(71-94). In the lupus-prone (SWR x NZB)F1 (SNF1) thymus, introduction of the lupus TCR transgene caused no deletion, but marked down-regulation of the Tg TCR and up-regulation of endogenous TCRs. Paradoxically, autoimmune disease was suppressed in the alphabetaTCR Tg SNF1 mice with induction of highly potent regulatory T cells in the periphery. By contrast, in the MHC-matched, normal (SWR x B10. D2)F1 (SBF1), or in the normal SWR backgrounds, marked deletion of transgenic thymocytes occurred. Thymic lymphoid cells of the normal or lupus-prone mice were equally susceptible to deletion by anti-CD3 Ab or irradiation. However, in the steady state, spontaneous presentation of naturally processed peptides related to the nucleosomal autoepitope was markedly greater by thymic dendritic cells (DC) from normal mice than that from lupus mice. Unmanipulated thymic DC of SNF1 mice expressed lesser amounts of MHC class II and costimulatory molecules than their normal counterparts. These results indicate that apoptotic nucleosomal autoepitopes are naturally processed and presented to developing thymocytes, and a relative deficiency in the natural display of nucleosomal autoepitopes by thymic DC occurs in lupus-prone SNF1 mice.

SLE: translating lessons from model systems to human disease

Systemic lupus erythematosus (SLE, lupus) results from immune-mediated damage to multiple organs. Its pathogenesis should be viewed as a series of steps, beginning with impaired immune regulation that permits self-reactive T-B-cell activation, which results in the production of autoantibodies. Activated T and B cells then infiltrate tissues, which along with autoantibody and immune complex deposition, triggering local events that ultimately cause organ damage. Although improved understanding of early autoimmune events might open up avenues for disease prevention, future investigations must focus on the mechanisms of end-organ damage in model systems and how to translate this knowledge into human disease. Understanding the mechanisms of each pathogenetic step would provide a rational basis for the development of disease stage-specific diagnostic markers and treatments.

[Specificities and clinical significance of autoantibodies directed against histones]

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the occurrence of numerous autoantibodies directed against nuclear antigens. Anti-histone antibodies (AHA) are as prevalent as their anti-dsDNA counterparts in SLE. Despite their frequency and potential importance, there have not been given much attention to AHA until recently. Nucleosomes, the fundamental repeating units of the chromatin, are formed of complexes of histones and DNA. The nucleosome core particle is composed of a central tetramer of 2 molecules each of H3 and H4 flanked by 2 dimers of H2A and H2B and surrounded by 2 superhelical turns of approximately 146 base pairs of DNA. The full nucleosome contains a molecule of H1 located at the point where DNA enters and exits the nucleosome. Recent studies have shown that the post transcriptional modification of histone changes chromatin structure to regulate transcription and the concept of this mechanism "epigenetics" has become center of attention in the field of basic cell biology. There have been described diverging specificities of AHA. Many attempts to locate antigenic determinants recognized by AHA have been made and H1 and H2B have been thought as common targets in lupus patients. Studies on murine models of lupus have shown several interesting findings. The universal epitope is located on H2B in (NZBxNZW)F1 mice. In addition to core histones, MRL-MP/Fas(lpr) mice develop high titers of autoantibodies to H1. Autoimmunity to chromatin regularly involves humoral immune responses directed against H1. These histones appear to be an early (possibly initial trigger) autoantigen for this autoimmune response in lupus.

Correlation between the expression of the histone H4 mRNA variant H4-v.1 and the levels of histone H4-(86-100) and H4-(89-102) (OGP) in various rat tissues and alveolar macrophages

We studied the expression of the osteogenic and antinociceptive C-terminal histone H4-related peptide fragments, H4-(89-102) (OGP) and H4-(86-100), respectively, within various rat tissues and isolated alveolar macrophages (AM) by radioimmunoassay (RIA). OGP was located mainly within the bone marrow, spleen, thymus, and lungs whereas H4-(86-100) was more concentrated within the bone marrow, lymph nodes, spinal cord, pituitaries and thymus. The expression pattern of the two peptides showed similarities with the tissue expression pattern of the histone H4 mRNA variant H4-v.1. In rat AM, OGP and H4-(86-100) levels were significantly stimulated (2.6- and 1.9-fold, respectively) by LPS (1 microg/ml), along with H4-v.1 mRNA (4.1-fold), but not whole histone H4 (1.1-fold) nor total histone H4 mRNA (1.1-fold). The results suggest that H4-v.1 mRNA may play a role in the synthesis of the naturally occurring peptides H4-(86-100) and OGP via the alternative translation product H4-(84-102), but not whole histone H4.

Very low-dose tolerance with nucleosomal peptides controls lupus and induces potent regulatory T cell subsets

We induced very low-dose tolerance by injecting lupus prone (SWR x NZB)F1 (SNF1) mice with 1 mug nucleosomal histone peptide autoepitopes s.c. every 2 wk. The subnanomolar peptide therapy diminished autoantibody levels and prolonged life span by delaying nephritis, especially by reducing inflammatory cell reaction and infiltration in kidneys. H4(71-94) was the most effective autoepitope. Low-dose tolerance therapy induced CD8+, as well as CD4+ CD25+ regulatory T (Treg) cell subsets containing autoantigen-specific cells. These adaptive Treg cells suppressed IFN-gamma responses of pathogenic lupus T cells to nucleosomal epitopes at up to a 1:100 ratio and reduced autoantibody production up to 90-100% by inhibiting nucleosome-stimulated T cell help to nuclear autoantigen-specific B cells. Both CD4+ CD25+ and CD8+ Treg cells produced and required TGF-beta1 for immunosuppression, and were effective in suppressing lupus autoimmunity upon adoptive transfer in vivo. The CD4+ CD25+ T cells were partially cell contact dependent, but CD8+ T cells were contact independent. Thus, low-dose tolerance with highly conserved histone autoepitopes repairs a regulatory defect in systemic lupus erythematosus by generating long-lasting, TGF-beta-producing Treg cells, without causing allergic/anaphylactic reactions or generalized immunosuppression.

Nucleosome, the main autoantigen in systemic lupus erythematosus, induces direct dendritic cell activation via a MyD88-independent pathway: consequences on inflammation

Nucleosome is the major autoantigen in systemic lupus erythematosus. It is found as a circulating complex in the sera of patients and seems to play a key role in disease development. In this study, we show for the first time that physiologic concentrations of purified nucleosomes directly induce in vitro dendritic cell (DC) maturation of mouse bone marrow-derived DC, human monocyte-derived DC (MDDC), and purified human myeloid DC as observed by stimulation of allogenic cells in MLR, cytokine secretion, and CD86 up-regulation. Importantly, nucleosomes act as free complexes without the need for immune complex formation or for the presence of unmethylated CpG DNA motifs, and we thus identified a new mechanism of DC activation by nucleosomes. We have clearly demonstrated that this activation is nucleosome-specific and endotoxin-independent. Particularly, nucleosomes induce MDDC to secrete cytokines known to be detected in high concentrations in the sera of patients. Moreover, activated MDDC secrete IL-8, a neutrophil chemoattractant also detected in patient sera, and thus might favor the inflammation observed in patients. Both normal and lupus MDDC are sensitive to nucleosome-induced activation. Finally, injection of purified nucleosomes to normal mice induces in vivo DC maturation. Altogether, these results strengthen the key role of nucleosomes in systemic lupus erythematosus and might explain how peripheral tolerance is broken in patients.

Increase in activated CD8+ T lymphocytes expressing perforin and granzyme B correlates with disease activity in patients with systemic lupus erythematosus

OBJECTIVE

Cytotoxic T lymphocyte-mediated killing using granzyme B has recently been proposed to be a preferential and selective source of autoantigens in systemic autoimmune diseases, including systemic lupus erythematosus (SLE), while other reports have indicated that cytolytic activity in SLE patients was decreased. The aim of this study was to examine the phenotypic and functional status of the CD8+ T cells in SLE patients.

METHODS

Phenotype analysis of CD8+ T cells was carried out using flow cytometry. The cytotoxic potential of CD8+ T cells and its consequences were examined in redirected-killing experiments. SLE patients with quiescent disease (n = 41) were compared with SLE patients with active disease (n = 20), normal individuals (n = 36), and control patients with vasculitis (n = 14). Cytotoxic CD8+ T cell differentiation was examined by coculture with differentiated dendritic cells (DCs) in the presence of SLE patient sera.

RESULTS

Patients with disease flares were characterized by higher proportions of perforin- and/or granzyme B-positive lymphocytes with a differentiated effector phenotype (CCR7- and CD45RA+). The frequency of these cells in peripheral blood correlated with clinical disease activity as assessed by the SLE Disease Activity Index. These cells generated high amounts of soluble nucleosomes as well as granzyme B-dependent unique autoantigen fragments. Finally, the activation of DCs with serum from a patient with active lupus induced granzyme B expression in CD8+ T lymphocytes.

CONCLUSION

DCs generated in the presence of sera from SLE patients with active disease could promote the differentiation of CD8+ effector T lymphocytes that are fully functional and able to generate SLE autoantigens. Our data disclose a new and pivotal role of activated CD8+ T lymphocytes in SLE pathogenesis.

T-helper cell intrinsic defects in lupus that break peripheral tolerance to nuclear autoantigens

Special populations of T helper cells drive B cells to produce IgG class switched, pathogenic autoantibodies in lupus. The major source of antigenic determinants (epitopes) that trigger interactions between lupus T and B cells is nucleosomes of apoptotic cells. These epitopes can be used for antigen-specific therapy of lupus. Secondly, the autoimmune T cells of lupus are sustained because they resist anergy and activation-induced programmed cell death by markedly upregulating cyclooxygenase (COX) 2 along with the antiapoptotic molecule c-FLIP. Only certain COX-2 inhibitors block pathogenic anti-DNA autoantibody production in lupus by causing death of autoimmune T helper cells. Hence COX-2 inhibitors may work independently of their ability to block the enzymatic function of COX-2, and structural peculiarities of these select inhibitors may lead to better drug discovery and design.

Nucleosome-specific regulatory T cells engineered by triple gene transfer suppress a systemic autoimmune disease

The mechanisms of systemic autoimmune disease are poorly understood and available therapies often lead to immunosuppressive conditions. We describe here a new model of autoantigen-specific immunotherapy based on the sites of autoantigen presentation in systemic autoimmune disease. Nucleosomes are one of the well-characterized autoantigens. We found relative splenic localization of the stimulative capacity for nucleosome-specific T cells in (NZB x NZW)F(1) (NZB/W F(1)) lupus-prone mice. Splenic dendritic cells (DCs) from NZB/W F(1) mice spontaneously stimulate nucleosome-specific T cells to a much greater degree than both DCs from normal mice and DCs from the lymph nodes of NZB/W F(1) mice. This leads to a strategy for the local delivery of therapeutic molecules using autoantigen-specific T cells. Nucleosome-specific regulatory T cells engineered by triple gene transfer (TCR-alpha, TCR-beta, and CTLA4Ig) accumulated in the spleen and suppressed the related pathogenic autoantibody production. Nephritis was drastically suppressed without impairing the T cell-dependent humoral immune responses. Thus, autoantigen-specific regulatory T cells engineered by multiple gene transfer is a promising strategy for treating autoimmune diseases.

Intravenous Injection of a D1 Protein of the Smith Proteins Postpones Murine Lupus and Induces Type 1 Regulatory T Cells

T cells that recognize nucleoproteins are required for the production of anti-dsDNA Abs involved in lupus development. SmD1 83-119 (a D1 protein of the Smith (Sm) proteins, part of small nuclear ribonucleoprotein) was recently shown to provide T cell help to anti-dsDNA Abs in the NZB/NZW model of lupus. Using this model in the present study, we showed that high dose tolerance to SmD1 (600-1000 microg i.v. of SmD1(83-119) peptide/mo) delays the production of autoantibodies, postpones the onset of lupus nephritis as confirmed by histology, and prolongs survival. Tolerance to SmD1 83-119 was adoptively transferred by CD90+ T cells, which also reduce T cell help for autoreactive B cells in vitro. One week after SmD1 83-119 tolerance induction in prenephritic mice, we detected cytokine changes in cultures of CD90+ T and B220+ B cells with decreased IFN-gamma and IL-4 expression and an increase in TGFbeta. Increased frequencies of regulatory IFN-gamma+ and IL10+ CD4+ T cells were later detected. Such regulatory IL-10+/IFN-gamma+ type 1 regulatory T cells prevented autoantibody generation and anti-CD3-induced proliferation of naive T cells. In conclusion, these results indicate that SmD1 83-119 peptide may play a dominant role in the activation of helper and regulatory T cells that influence autoantibody generation and murine lupus.

Treatment of murine lupus using nucleosomal T cell epitopes identified by bone marrow-derived dendritic cells

OBJECTIVE

Systemic lupus erythematosus (SLE) is characterized by the existence of a heterogeneous group of autoantibodies directed against intact nuclear structures, such as nucleosomes. The most prominent of these autoantibodies are those directed against double-stranded DNA (dsDNA) and histones. The majority are of the IgG isotype and show affinity maturation, both of which are known hallmarks of T cell help. Much evidence suggests that the nucleosome is a major candidate autoantigen in SLE. In this study, a novel strategy was used to identify the critical CD4+ T cell autoepitopes in nucleosomes. In addition, peptide-based therapy was then performed in a lupus animal model.

METHODS

Bone marrow (BM)-derived dendritic cells (DCs) were used to examine the self-T cell responses against nucleosomes and to characterize the T cell epitope(s) of nucleosomes in (NZB x NZW)F1 (BWF1) mice.

RESULTS

Several potential auto-T cell epitopes of core histone proteins (H2A, H2B, H3, and H4) were identified. Nucleosome-pulsed BM-derived DCs elicited release of interleukin-4 and interferon-gamma, representing a Th0 (i.e., mixed Th1 and Th2) pattern of cytokine production. In addition, intradermal immunization of BWF1 mice with the H3(111-130) peptide not only suppressed the level of anti-dsDNA and anti-single-stranded DNA IgG, but also significantly delayed the progress of glomerulonephritis in lupus-prone BWF1 mice.

CONCLUSION

These results will help in understanding how pathogenic autoimmune responses develop in spontaneous SLE. This may potentially open the way to T cell-based immunotherapy for lupus.

Extranuclear detection of histones and nucleosomes in activated human lymphoblasts as an early event in apoptosis

OBJECTIVE

To evaluate the presence of histones and nucleosomes in cell lysates of freshly isolated peripheral blood mononuclear cells (PBMC), fully activated lymphoblasts, or lymphoblasts after induction of apoptosis.

METHODS

Each histone class (H1, H2A, H2B, H3, and H4) was detected by western blot analysis with specific antibodies. Annexin V/propidium iodide (PI) staining was performed for each treatment to distinguish viable, early, and late apoptotic, and necrotic cells. DNA degradation was evaluated by PI staining in a hypotonic buffer.

RESULTS

All five histones were detected in cell lysates of activated lymphoblasts in higher concentrations than in lysates of PBMC. An additional significant increase of H2A, H2B, H3, H4, and complete nucleosomes in cell lysates of lymphoblasts was found during interleukin (IL)2 deprivation for 8 or 24 hours. The content of these histones or nucleosomes in cell lysates decreased after delayed IL2 readdition. H1 content in cell lysates was not affected by IL2 deprivation or addition. Quantities of H2A, H2B, H3, and H4 in cell lysates correlated significantly with signs of early apoptosis. UV-B light exposure or etoposide treatment of lymphoblasts resulted in a distinct increase for each histone class in cell lysates compared with standard curves. No bands for post-translationally modified histones were detected in cell lysates in contrast with signals in nuclear preparations.

CONCLUSION

Extranuclear accumulation of histones and nucleosomes is an early event of apoptosis in human lymphoblasts. Dysregulation of early apoptosis might support the induction of autoimmunity against nuclear components.

Nucleosomes in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by the development of a large array of autoantibodies that primarily are directed against the whole chromatin (antinucleosome) and its individual components, dsDNA and histones. Apoptotic defects and impaired removal of apoptotic cells could contribute to an overload of autoantigens (and in particular of nucleosomes) in circulation or in target tissues that could become available to initiate an autoimmune response. In susceptible individuals, this can lead to autoantibody-mediated tissue damage. In addition to intrinsic or secondary apoptosis/apoptotic cell removal defects, certain apoptotic stimuli (eg, UV, viruses) could lead to posttranscriptional modifications that generate autoantigen cryptic fragments for which cells of the immune system have not been tolerized. Besides their role as a major immunogen in lupus, nucleosomes participate in antibody-mediated renal pathogenicity and act as a bridging molecule that recognizes heparin sulfate/collagen V components of the glomerular basement membrane. New tools that were developed to detect antinucleosome antibodies in the serum of patients (by ELISA) have shown the specificity and the high sensitivity of antinucleosome antibody reactivity in SLE. In particular, antinucleosome could be a useful marker of patients who have SLE and lack anti-dsDNA antibodies, a prognosis marker for imminent relapse, and a diagnosis marker of lupus nephritis.

Antigen-specific cytometry—New tools arrived!

Until recently, immunofluorescence-based cytometry and cell sorting, which have now found their place in the repertoire of state-of-the-art technologies, have mostly served to identify and assess subsets of leukocytes and thereby to evaluate rather systemic changes of the immune system. A more detailed defined evaluation of immune responses was not possible for a long time. In particular, a focus of the cytometric analysis on those lymphocytes specifically recognizing a defined antigen was hampered due to technical limitations. Yet, traditional methods for the analysis of antigen-specific lymphocytes typically relied upon measurements of proliferation or cytokine expression in bulk cultures. In recent times, this hindrance has been overcome both for B and T lymphocytes. We review here the emerging field of antigen-specific cytometry and describe the most widely used state of the art and future technologies that offer exciting new options to analyze and isolate specifically those lymphocytes that are directly involved in the immune reaction to given antigens, options that have already spurred research, diagnosis, and therapy beyond scope.

Human lupus T cells resist inactivation and escape death by upregulating COX-2

Autoimmune T-helper cells drive pathogenic autoantibody production in systemic lupus erythematosus (SLE), but the mechanisms maintaining those T cells are unknown. Autoreactive T cells are normally eliminated by functional inactivation (anergy) and activation-induced cell death (AICD) or apoptosis through death receptor (Fas) signaling. However, mutations in the genes encoding Fas and its ligand (FasL) are rare in classical SLE. By gene microarray profiling, validated by functional and biochemical studies, we establish here that activated T cells of lupus patients resist anergy and apoptosis by markedly upregulating and sustaining cyclooxygenase-2 (COX-2) expression. Inhibition of COX-2 caused apoptosis of the anergy-resistant lupus T cells by augmenting Fas signaling and markedly decreasing the survival molecule c-FLIP (cellular homolog of viral FLICE inhibitory protein). Studies with COX-2 inhibitors and Cox-2-deficient mice confirmed that this COX-2/FLIP antiapoptosis program is used selectively by anergy-resistant lupus T cells, and not by cancer cells or other autoimmune T cells. Notably, the gene encoding COX-2 is located in a lupus-susceptibility region on chromosome 1. We also found that only some COX-2 inhibitors were able to suppress the production of pathogenic autoantibodies to DNA by causing autoimmune T-cell apoptosis, an effect that was independent of prostaglandin E(2) (PGE(2)). These findings could be useful in the design of lupus therapies.

Peptide-based immunotherapy of systemic lupus erythematosus

Current drug-based therapy for systemic lupus erythematosus (SLE) are non-specific and often counterbalanced by adverse effects. Current research aims at developing specific treatments that target deleterious cells only and not the whole immune system. This strategy requires the identification of sequences derived from major lupus autoantigens, responsible for the activation of autoreactive B and T cells. This review summarizes the identification and characterization of peptides, which are able to modulate T cells ex vivo, and describes the promising results obtained after administration of some of these peptides in lupus mice. Although these therapeutic trials are encouraging, the precise mode of action of peptide-based immunotherapy is still elusive. Here, we discuss the possible mechanisms leading to T-cell tolerance induction and the feasibility of extending the success of peptide-based therapy from animal models to human.

Intravenous immunoglobulin abrogates dendritic cell differentiation induced by interferon-? present in serum from patients with systemic lupus erythematosus

OBJECTIVE

Alterations in the function of dendritic cells (DCs) may explain the systemic autoimmune responses that characterize systemic lupus erythematosus (SLE). Even though several reports have documented the beneficial effect of intravenous immunoglobulin (IVIG) in SLE, the underlying mechanisms of action remain poorly understood. Considering the effect of serum factors, including interferon-alpha (IFNalpha), on the activity of DCs, we investigated the effects of IVIG on the differentiation of DCs mediated by serum from SLE patients.

METHODS

DCs were differentiated from peripheral blood monocytes obtained from SLE patients and from healthy blood donors, in the presence of SLE serum. IVIG was used at a concentration of 0.15 mM. A functional assay was performed to assess the inhibitory effect of IVIG on the uptake of nucleosomes by DCs.

RESULTS

IVIG interfered with the differentiation of DCs from SLE patients and healthy donors cultured in the presence of SLE serum. Treatment of DCs with IVIG inhibited the ingestion of nucleosomes by immature DCs, by up to 36%.

CONCLUSION

The present findings indicate that IVIG, by down-regulating the IFNalpha-mediated differentiation of DCs and by inhibiting uptake of nucleosomes, may exert an essential immunoregulatory effect in SLE patients at the onset of the immune response, at the DC level. Given the critical role of HLA molecules and the costimulatory signals delivered by CD80 and CD86 in optimal antigen presentation and T cell activation, inhibition of expression of HLA and CD80/CD86 on DCs by IVIG offers a plausible explanation for the efficacy of IVIG in SLE and other immune-mediated inflammatory conditions.

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

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

Triggers for anti-chromatin autoantibody production in SLE

The formation of autoantibodies against chromatin is the main feature of systemic lupus erythematosis (SLE), an autoimmune disease, which is T-cell dependent and autoantigen-driven. Historically, antibodies against dsDNA, one of the components of chromatin, are considered as a hallmark of SLE. However, dsDNA is poorly immunogenic. Nucleosome-specific T helper cells have been identified. These T cells propagate not only nucleosome-specific antibodies, but also anti-dsDNA antibodies. Nucleosomes are formed during apoptosis by cleavage of chromatin, and evidence of disturbed apoptosis has been found especially in certain murine models of lupus. In addition to an increased rate of apoptosis, autoimmunity against chromatin might also result from an impaired phagocytosis of apoptotic material, for which strong evidence has been provided by studies in certain knock-out mice (C1q, SAP, Dnase I). The induction of an immune response to nucleosomes could be enhanced by modifications of histones or DNA during apoptosis, altered presentation by antigen presenting cells or a viral infection. The release of nucleosomes and the formation of anti-chromatin autoantibodies result in formation of complexes, which bind to the glomerular basement membrane via heparan sulfate. This deposition incites glomerulonephritis, the most serious manifestation of SLE.

Neutralizing interferon alpha as a therapeutic approach to autoimmune diseases

Therapeutic antibodies directed against tumor necrosis factor alpha (TNF-alpha) for the treatment of rheumatoid arthritis, and against the human EGF receptor-2 (HER2) receptor for the treatment of breast cancer have provided significant clinical benefit for the patients. The success of these antibodies has also provided strong support for the possibility that increased activity of cytokines or growth factors is causally implicated in a variety of human diseases. Interferon alpha (IFN-alpha) is induced by viruses (linked by epidemiological studies to autoimmune diseases), has significant direct effects on both epithelial cells and the immune system, and then can be further induced by the autoantibodies and apoptotic cells generated by the actions of IFN-alpha. The direct and deleterious impact on target tissues, the ability to induce an autoimmune response, and the potential for a self-sustaining cycle of induction and damage suggests that IFN-alpha could be a pivotal factor in the development of autoimmune diseases. This review will evaluate the rationale for, possible approaches to, and safety concerns associated with, targeting interferon alpha (IFN-alpha) as a therapeutic strategy for the treatment of autoimmune diseases. While the approach may be applicable to several autoimmune diseases, there will be an emphasis on systemic lupus erythematosus and insulin dependent diabetes mellitus.

Major peptide autoepitopes for nucleosome-centered T and B cell interaction in human and murine lupus

The potential cross-reactivity of normal T and B cells to nuclear antigens is vast, probably due to their "education" by apoptotic cell antigens in generative lymphoid organs. Despite this "nucleocentric repertoire," as we call it, the peripheral immune system normally remains tolerant or ignorant of the products of apoptosis. However, the T helper (Th) cells, and also B cells of lupus, have a regulatory defect in the expression of CD40 ligand (CD40L). A sustained hyper-expression of CD40L by lupus T cells can be triggered by sub-threshold stimuli, and is associated with impaired phosphorylation of Cbl-b, a critical downregulatory molecule in T cell signal transduction. This CD40L hyper-expression abnormally prolongs co-stimulatory signals to autoimmune B cells, and it probably instigates APC (dendritic cells, resting anti-DNA B cells, and macrophages) to present apoptotic cell autoantigens in an immunogenic fashion. We have identified the dominant nucleosomal epitopes that are critical for cognate interactions between autoimmune Th cells and anti-DNA B cells in lupus. By scanning of overlapping synthetic peptides, and by mass spectrometry of naturally processed peptides, five major epitopes in nucleosomal histones were localized, namely H1'(22-42), H2B(10-33), H3(85-105), H4(16-39), and H4(71-94). The autoimmune T cells as well as B cells of lupus recognize these epitopes, and with age, autoantibodies against the peptide epitopes cross-react with nuclear autoantigens. Moreover, the peptide autoepitopes can be promiscuously presented and recognized by lupus T cells in the context of diverse MHC alleles. This cross-reactivity opens up the possibility of developing "universally" tolerogenic peptides for therapy of lupus in humans despite their MHC diversity. Indeed, tolerogenic therapy with a single histone peptide epitope can halt the progression of established glomerulonephritis in lupus-prone mice by "tolerance spreading" that inactivates a broad spectrum of autoimmune T and B cells in concert.

T cell reactivity to MHC class II-bound self peptides in systemic lupus erythematosus-prone MRL/lpr mice

The epitopes recognized by pathogenic T cells in systemic autoimmune disease remain poorly defined. Certain MHC class II-bound self peptides from autoimmune MRL/lpr mice are not found in eluates from class II molecules of MHC-identical C3H mice. Eleven of 16 such peptides elicited lymph node cell and spleen cell T cell proliferation in both MRL/lpr (stimulation index = 2.03-5.01) and C3H mice (stimulation index = 2.03-3.75). IL-2 and IFN-gamma production were detected, but not IL-4. In contrast to what was seen after immunization, four self peptides induced spleen cell proliferation of T cells from naive MRL/lpr, but not from C3H and C57BL/6.H2(k), mice. These peptides were derived from RNA splicing factor SRp20, histone H2A, beta(2)-microglobulin, and MHC class II I-A(k)beta. The first three peptides were isolated from I-E(k) molecules and the last peptide was bound to I-A(k). T cell responses, evident as early as 1 mo of age, depended on MHC class II binding motifs and were inhibited by anti-MHC class II Abs. Thus, although immunization can evoke peripheral self-reactive T cells in normal mice, the presence in MRL/lpr mice of spontaneous T cells reactive to certain MHC-bound self peptides suggests that these T cells actively participate in systemic autoimmunity. Peptides eluted from self MHC class II molecules may yield important clues to T cell epitopes in systemic autoimmunity.