Pathological lymphocyte activation by defective clearance of self-ligands in systemic lupus erythematosus

K. Yasutomo

Department of Immunology and Parasitology, School of Medicine, The University of Tokushima, 3–18–15 Kuramoto, Tokushima 770-8503, Japan. E-mail: yasumoto{at}basic.med.tokushima-u.ac.jp


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Systemic lupus erythematosus (SLE) is one of the autoimmune diseases extensively studied by immunologists and physicians. The main focus regarding SLE pathophysiology has been placed on abnormal cell surface receptor function on lymphocytes. However, recent studies have revealed that defective clearance of apoptotic cells causes self-antigen accumulation, which could trigger the activation of autoreactive lymphocytes. Thus, here we review current findings about the association of the defective clearance of autoantigens and SLE, focusing on mutations in the DNase I locus and their relationship to SLE.


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Autoimmune diseases are caused by defective genes, aberrant gene expression or regulation, and environmental factors [1, 2]. Autoimmune disease susceptibility is determined by the interplay of these factors, which eventually affect autoreactive lymphocyte activation status or cell death sensitivity [2, 3]. Such autoreactive lymphocytes attack cells by several mechanisms, which include hyperactivation or target cell inhibition. The cell or organ specificity is determined by the antigen expression pattern regulated by gene expression or antigen presentation. Several studies using organ-specific autoimmune-prone mice have demonstrated that autoantigens are specifically expressed on certain damaged organs [4, 5]. The activated lymphocytes obtained from such mice cause disease when transferred into normal mice. This supports the concept that cell-specific antigens are primary targets of organ-specific autoimmune diseases [6]. On the other hand, recent studies by Oono et al. [7] showed that transgenic mice with a single major histocompatibility complex (MHC) peptide could develop peripheral nervous system-specific autoimmune disease. These findings suggest that the differential antigen expression pattern among organs is not the only determinant for organ-specific autoimmune diseases.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by a broad variety of clinical symptoms and autoantibody production against nucleic acids, typically double-stranded (ds)DNA [1, 8]. Several lines of evidence indicate SLE development has a strong genetic basis. For example, familial aggregation studies indicate a sibling risk ratio of at least 10 times [9]. The genes that cause SLE have been intensively investigated by using newly identified microsatellite markers. There are several reported candidate SLE chromosomal loci that have been found using these markers in the mouse and human genomes [8]. Although these studies suggested that several candidate genes are responsible for SLE development or progression, it is unclear what genetic defect type(s) is responsible for causing all forms of SLE.

It is clear that SLE development is caused by aberrant immune responses, which include autoreactive T and B cells. This is supported by clinical laboratory findings of high serum titres of various autoantibodies in SLE patients [1]. Furthermore, it is known that there are polyclonal autoreactive T cells in SLE patients [10]. Based on these observations, over the last decade, several studies using gene knock-out technology have focused on genes associated with cell death or the lymphocyte activation threshold. According to these studies, several genes have been reported to be related to systemic autoimmune disease development (Table 1Go) [1138]. However, we have yet to succeed in identifying genes responsible for causing typical human SLE (Table 1Go).


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TABLE 1. Mouse and human gene mutations that cause systemic autoimmune diseasesa

 
Recent studies have shown that most of the peripheral CD4+ or CD8+ T cells have a potential to respond to self-antigens [3942] and persistence of such self-antigens in vivo can provoke human or murine SLE (Table 1Go) [2931, 33, 34]. Furthermore, several groups have shown that the T-cell receptor (TCR) or B-cell receptor (BCR) signalling pathway itself is abnormal in SLE patients [43, 44], which may accelerate the autoimmune responses elicited by the abnormal autoantigen persistence. These recent findings in basic and clinical immunology would cause the reconsideration of the importance of antigen clearance and persistence as a cause of SLE. Thus, I would like to review the abnormal lymphocyte responses seen in SLE patients focusing on TCR or BCR signalling and defective self-antigen clearance.


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Defective T-cell responses in lupus patients
The immune system responds to antigens that engage specialized receptors on both the T-cell and B-cell surface [45]. The TCR or BCR engagement induces various interacting intracellular biochemical events that transmit an extracellular signal, which can result in cell activation, proliferation, secretion of soluble mediators, phenotypic changes, acquisition of effector functions, anergy and programmed cell death [4548]. The TCR or BCR stimulation outcome can vary considerably depending on the degree and extent of integration of other membrane receptor-initiated specific accessory signals. In particular, CD28–CD80/86 and CD40–CD40 ligand interaction are important for complete T-cell and B-cell activation, respectively [49]. Because TCR- or BCR-mediated signalling events direct these diverse but equally important outcomes, it is likely that the diverse cellular aberrations described in lupus patients reflect signalling defect(s) responsible for the disease pathogenesis. Such defects might be derived from the abnormal expression of a signalling molecule(s) due to either defective gene(s) or defective regulation of expression.

Tsokos et al. [44, 50] studied TCR/CD3-mediated signalling events to identify lupus T-cell primary abnormalities. Using the anti-human CD3 monoclonal antibody (mAb), they showed that lupus T cells significantly exhibited increased Ca2+ responses compared with the T-cell responses from patients with non-SLE autoimmune disease [50]. Furthermore, anti-CD3 mAb increased Ca2+ fluxes in autoantigen-specific lupus T-cell clones, but not in autoantigen-specific T-cell clones derived from subjects with other autoimmune diseases. Furthermore, they also demonstrated that lupus TCR/CD3 signalling is defective in tyrosine-phosphorylated protein production, which is necessary for proper T-cell activation [44]. In detail, T-cell stimulation in SLE patients results in significantly enhanced production of tyrosine-phosphorylated cellular proteins and consists of an early elevated response as well as a steep decrease to baseline phosphorylation levels. In contrast, protein tyrosine phosphorylation in normal T cells gradually increases during the same period [44]. Taken together, these results suggest that lupus T cells have an increased sensitivity for proximal TCR signalling in terms of peak intensity or TCR signalling duration, which would elicit abnormally high T-cell activation that could cause tissue damage.

Regulation of T-cell activation is accomplished by cell surface/intracellular molecules of T cells and other cell types. Filaci et al. [51] showed that the inhibitory function of CD8+ cells in lupus patients is low, which would contribute to lupus development. Recent advances regarding suppressor T cells, such as CD4+ CD25+ T cells, revealed that CD4+ CD25+ T cells play a pivotal role in autoimmune disease development in mice [52]. Several groups reported that human blood also has CD4+ CD25+ T cells with suppressive function [52]. So far, the contribution of CD4+ CD25+ T cells to lupus has not been reported, but this cell population will now be closely monitored in terms of defective T-cell responses in lupus patients.

TCR/CD3{zeta} chain deficiency in lupus T cells
Lupus T cells have a significant amount of tyrosine phosphorylation after TCR ligation [44]. Surprisingly, analysis of the TCR/CD3-initiated protein tyrosine phosphorylation reaction revealed TCR{zeta} chain absence or deficiency in lupus T-cell lysates [44]. In contrast, the TCR{zeta} chain was always present in T-cell lysates from normal subjects and patients with rheumatic disorders other than SLE. The TCR{zeta} chain deficiency is attributable to the low expression of TCR{zeta} mRNA in lupus T cells [44]. Jensen et al. [53] showed that T cells lacking TCR{zeta}, but expressing sufficient amounts of CD3{varepsilon}, transduce early signalling events, resulting in enhanced tyrosine phosphorylation of proteins compared with cells that were preferentially signalled via the TCR{zeta} chain. Thus, the deficient TCR{zeta} chain may be responsible for the increased amount of tyrosine-phosphorylated proteins after TCR ligation that is seen in lupus T cells (although the TCR{zeta} reconstitution assay still needs to be performed using lupus T cells).

There is another attractive possibility to connect the TCR{zeta} defective expression to SLE. The intrathymic positive and negative selection of thymocytes may be impaired due to the TCR{zeta} defective expression because the TCR{zeta} chain is absolutely required for both selection steps in mouse studies [54, 55]. In this case, the decreased negative selection might be responsible for the increased autoreactive T cells in lupus patients and the decreased positive selection for the decreased lupus T-cell response to exogenous antigens. Defective TCR{zeta} expression may be due to polymorphisms in the TCR{zeta} gene or adjacent non-coding regions. Interestingly, genetic studies of the TCR{zeta} chain showed that polymorphisms in the 906-bp TCR{zeta}-chain 3' untranslated region were significantly higher in SLE T cells than in non-SLE T cells [56]. Further studies should explore if these polymorphisms impact the TCR{zeta} chain expression.

Signalling defects of lupus B cells
A study on B-cell BCR-mediated signalling supports the view that lupus B cells display signalling defects, providing molecular insight into the characteristic hyperactivity of such cells and, possibly, the primary cause of the pathogenesis of the disease. The BCR-mediated signalling abnormalities are remarkably similar to those initiated by anti-CD3 Abs in lupus T cells [43]. Specifically, BCR (surface IgM or IgD) engagement either with anti-human IgM or anti-IgD Abs resulted in significantly increased Ca2+ release, minor increased inositol 1,4,5-trisphosphate (InsP3) production and enhanced production of tyrosine-phosphorylated cellular proteins [43]. Increased phosphorylation of signalling molecules via the antigen receptor that is also seen in lupus T cells may contribute to abnormal lymphocyte activation. A future task includes examining why the lupus B-cell signalling molecules are hyperphosphorylated.

CD19 is a B-cell-specific member of the Ig superfamily expressed by early pre-B cells from the time of heavy chain rearrangement until plasma cell differentiation. The CD19 cell surface density is tightly regulated during B-cell differentiation [57]. After B-cell maturation, cellular activation induced by various stimuli, such as anti-IgM Abs, lipopolysaccharide (LPS), and interleukin 4 (IL-4), does not affect CD19 expression in either mice or humans [58]. None the less, the B1 subset of mouse B cells expresses CD19 at levels 60% higher than conventional B cells [58]. Mouse lines that overexpress CD19 have been generated by the B-cell-specific expression of a human CD19 (hCD19) transgene [59]. Since hCD19 and mouse CD19 (mCD19) are functionally equivalent in vivo when expressed at comparable densities [60], these different mouse lines express CD19 at various cell surface densities. In these mice, CD19 expression levels correlate directly with altered B-cell function, hyperactivity and autoantibody production [58]. Dose-dependent changes in B-cell development and function resulting from in vivo CD19 overexpression presumably result from the fact that the CD19 cytoplasmic domain is a B-cell central regulatory component upon which multiple signalling pathways converge [61]. Perhaps more importantly, CD19 regulates an Src family protein tyrosine kinase activation loop in resting and Ag receptor-stimulated B cells that establishes basal signalling thresholds [62]. On the other hand, a major regulatory function for CD22/SHP1 (SH2-containing protein tyrosine phosphatase 1) is to down-regulate CD19 tyrosine phosphorylation following B-cell antigen receptor engagement [63]. Thus, it would be important to evaluate if the aberrant balance between the CD19 and CD22 pathway contributes to SLE development.


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During intrathymic development, T cells expressing moderate affinity receptors for self-MHC/peptide ligands are positively selected, survive and differentiate (positive selection), whereas the T-cell majority with little or no affinity for such ligands undergo apoptotic death by neglect [64, 65]. In contrast, T cells expressing TCR with high affinity for self-MHC/peptide ligands are deleted by apoptosis (negative selection). Only a small fraction of T cells (~5%) [64, 65] can migrate to the periphery, constituting the mature T-cell pool. One hypothesis is that the exported naive T cells from the thymus persist in a dormant state in the secondary lymphoid organs, unaware of self-antigens until engaged by activated antigen-presenting cells displaying foreign antigenic peptides. This assumption has recently been challenged by the demonstration that low-grade recognition of self-MHC/peptide ligands and covert signals delivery, those that induce proliferation but fail to provoke antigen-specific overt signals, are required for tissue damage [3942]. Initially, the role of such an interaction between TCR and self-MHC/peptide ligands had been considered to be essential for T-cell survival. However, recent studies have called into question the strict necessity of self-MHC/peptide ligand recognition for peripheral naive CD4+ T-cell survival [42, 66]. Furthermore, several reports demonstrated that such an interaction is not necessary for memory CD8+ T-cell survival [67].

The relevance of homeostatic naive T-cell anti-self proliferation to autoimmunity extensively depends on whether the proliferating cells acquire effector function and differentiate to the activated/memory phenotype. Several studies in which TCR transgenic CD8+ or CD4+ T cells were transfused to lymphopenic syngeneic hosts have provided some clues [42, 68, 69]. Proliferating TCR transgenic CD8+ T cells kill target cells ex vivo in a peptide- and TCR-dependent manner, and express interferon-{gamma} (IFN-{gamma}) after anti-CD3 mAb stimulation. In vivo, they also acquire several, but not all, activated/memory T-cell phenotypic markers. Even polyclonal CD8+ or CD4+ T cells undergoing homeostasis-driven proliferation acquire activated/memory phenotypes, and such polyclonal CD8+ T cells are able to secrete IFN-{gamma} rapidly after anti-CD3 mAb stimulation and kill concanavalin A (ConA)-coated syngeneic targets [68, 70]. Importantly, such acquisition of T-cell memory/effector phenotypes after homeostatic proliferation does not cause autoimmune tissue damage (Yasutomo et al., unpublished observation), which suggests that such activation is not complete enough to damage cells.

The T-cell homeostatic proliferation may induce continuous T-cell stimulation by self-antigens and attainment of a replicative senescence state; however, such cells may be unable to act as efficient homeostatic proliferation inhibitors. Indeed, mice (and humans) with lupus show an expedited accumulation of activated/memory phenotype cells with clonal expansions [71]. Lymphopenia often seen in SLE patients may also trigger homeostatic anti-self T-cell proliferation. Recent studies clearly showed that the T-cell development outcome, activation or proliferation, is dependent on the affinity and avidity between the TCR and MHC-ligand complex [7274]. Thus, the findings that T cells proliferate upon self-ligand recognition suggest that the continuous presence of self-ligands elicits strong T-cell responses, resulting in autoimmune disease inducement. Indeed, recent studies strongly support this possibility.


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DNase I deficient patients: gene mutations and clinical features
Napirei et al. [33] reported that DNase I deficient mice develop an SLE-like syndrome, even if the mutation is heterozygous. These mice have a high titre of anti-dsDNA antibodies and develop severe glomerulonephritis, which resembles human SLE. Based on this information, we scanned the DNase I coding sequence and exon/intron boundaries for mutations. We identified an A to G transversion in exon 2 at position 172 of the cDNA sequence, which replaces a lysine (AAG) with a stop codon (TAG) at residue 5 (K5X) in two SLE patients (Fig. 1Go) [34]. Restriction enzyme analysis showed that the gene mutation is heterozygous for both patients. These female patients, age 13 (patient 1) and age 17 (patient 2), were previously diagnosed as having SLE based on both clinical features and a high serum titre of anti-dsDNA and SS-A antibodies [75]. Patient 1 developed subclinical Sjögren's syndrome, but other clinical features of patient 1 and 2 were similar to those of other SLE patients. Thus, we think that SLE patients with the DNase I mutation do not have unique clinical symptoms. Additional analysis of the clinical features of other SLE patients with the DNase I mutation is necessary to test this hypothesis.



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FIG. 1. DNase I mutation in SLE patients. A schematic of the DNase I gene indicates the location of exon 1 and 2. There are nine exons, with the last exon shown. A mutation was discovered in exon 2, which is an A to G conversion that generates a stop codon at amino acid position 5. Two SLE patients have this mutation in the DNase I gene.

 

DNase I deficient patients: laboratory findings
The DNase I mutation in patient 1 and 2 is heterozygous, so the effect of the mutation on DNase I activity was examined in the sera from the two patients. As expected from this type of mutation, the patients had significantly lower levels of DNase I activity compared with other SLE patients without the DNase I mutation and healthy controls (Table 2Go). Similar to the findings in other studies, the DNase I activity in the SLE patients without the DNase I mutation was lower than that of healthy controls [76, 77], although the DNase I gene was not completely characterized in these studies. Since the DNase I serum level activity may be affected by many factors, such as drugs, disease stage or DNase I inhibitors [76, 78], we measured the DNase I enzymatic activity in transformed B cells from these patients. The B cells had only 30–50% of the DNase I activity as seen in controls (Table 2Go), showing that this heterozygous mutation in DNase I reduces the total enzymatic activity.


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TABLE 2. DNase1 activity in sera and transformed B cells and precursor frequency of T and B cells against nucleosomal antigensa

 

DNase I deficient patients: mechanism of autoimmunity
We determined if low DNase I activity had a specific effect on any of the defining SLE pathological characteristics by examining antibody titres against nucleosomal antigens and dsDNA in the two patients, SLE patients without DNase I mutations and in healthy controls. As shown in Table 2Go, the IgG titre against nucleosomal antigens was 7–8 times greater in the two patients with the DNase I mutation than in the other SLE patients, and 70–80 times greater than in the normal controls (Table 2Go). The dsDNA IgG titre in the two patients was also higher than in the other SLE patients (Table 2Go). To characterize further the possible link between low DNase I activity and SLE progression, the T-cell and B-cell precursor frequencies responsive to nucleosomal antigens were analysed by limiting dilution analysis. We observed an increased frequency of T and B cells against nucleosomal antigens (K. Yasutomo, unpublished observation). These results strongly suggest that low DNase I activity in these two patients contributes to the autoreactive T-cell and B-cell expansion against nucleosomal antigens.


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Increased nucleosomal antigens and autoimmunity
Aberrant rates of apoptosis and increased levels of free circulating chromatin have been reported in murine and human lupus [79], and mutations in the DNase I and C1q genes lead to SLE development in humans [30, 34]. These results and others suggest that efficient chromatin removal or the chromatin–protein complex is crucial to prevent SLE. For example, serum amyloid P component (SAP) deficient mice develop an SLE-like syndrome [31]. Two models can explain the SAP deficiency and SLE connection. First, SAP would participate in the chromatin solubilization, activating C1 through C4, and potentiating hepatic clearance through complement receptors. Thus, SAP deficiency would result in accumulation of apoptotic debris, which activates pre-existing autoreactive T and B cells. Second, SAP assists in C4b binding to chromatin, which as a complex binds bone marrow stromal cells by the C4b receptor. In the presence of SAP, immature autoreactive B cells acquire tolerance against chromatin through clonal deletion and/or anergy. In the case of SAP deficiency, chromatin cannot be recruited to the bone marrow, which results in autoreactive B-cell escape into the periphery and subsequent antigen-driven expansion.

Boes et al. [32] established mice that are deficient in secreting IgM, but that express surface IgM and IgD, and secrete other immunoglobulin classes. These mice were crossed with lupus-prone lymphoproliferative mice. The resulting progeny had elevated levels of IgG autoantibodies to dsDNA and histones, and abundant immune complex deposits in the glomeruli. Furthermore, the absence of secreted IgM resulted in IgG autoantibody accelerated development even in normal mice. The accelerated autoantibody responses in mice deficient in secreted IgM resemble the complement deficiency effect on autoimmune disease development. In humans and mice, early complement cascade component deficiencies, including C1q, C2 and C4, are associated with a high incidence of SLE [29, 30]. Complement promotes autoantigen removal and could reduce the chance that autoreactive B cells are activated. Intravenous injection of syngeneic apoptotic cells into normal mice induces a rapid antinuclear antibody (ANA) response [80], suggesting that the autoantigen source for the autoantibody response may be the apoptotic cells [81]. C1q can directly bind apoptotic blebs and complement activation is required for apoptotic cell clearance by macrophages [82], suggesting a critical role for complement in apoptotic cell clearance.

Mer (member of the Axl/Mer/Tyro3 receptor tyrosine kinase family) deficient mice also possess a high serum titre of anti-DNA antibodies (it is unknown if these mice develop pathological autoimmune responses) [28]. Since Mer is required for the engulfment and efficient apoptotic cell clearance, the defective chromatin clearance may induce overt activation of autoreactive lymphocytes in these mice.

Taken together, the defective clearance of nucleosomal antigens may result in the generation of anti-dsDNA antibodies, which leads to subsequent tissue damage. The significant numbers of autoreactive T cells against self-ligands, including nucleosomal antigens, are present in the normal body according to the results showing naive T-cell homeostatic proliferation. Thus, I would like to postulate that the degree of T-cell response against self-ligands is dependent on the TCR signalling duration or amount, as well as the affinity between the TCR and their ligands (Fig. 2Go). In the normal case, the TCR signalling duration or amount upon recognition of self-ligands fails to reach the cell damage activation threshold for T cells. This is because the TCR affinity is generally low and self-ligands are rapidly cleared from the body. However, the abnormal accumulation of self-ligands allows T-cell exposure for sufficient time or self-ligand quantity to induce pathological T-cell differentiation.



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FIG. 2. Duration or amount of TCR signalling is a determinant for a pathological T-cell response. The TCR signalling duration or amount increases the T-cell activation status [48]. The affinity to self-ligands and non-self-ligands is represented along the x-axis. The amount or duration of antigen in the body is indicated along the y-axis. The T cells that have low–mild affinity against self-antigens are positively selected in the thymus and become mature cells. T cells with high affinity to self-antigens die in the thymus. However, the long duration or high amount of self-antigens could allow mature T cells to reach the activation threshold. The pathological T cells are generated when these two parameters are beyond the threshold of certain T-cell activation as indicated by the shaded graph area.

 
As a final point, I would like to comment on why lymphocyte generation against nucleosomal antigens, predominantly an internal antigen, induces autoimmunity. There is little information on how anti-dsDNA antibodies are associated with SLE pathophysiology. Antinuclear specificity of disease-associated autoantibodies has lured investigators to one of the likely sources of autoreactive stimulation in SLE, leading to the development of two possible models. During the demise of cells that are either inadvertently damaged (ultraviolet burns) or intentionally targeted (programmed cell death), condensed chromatin is broken down into nucleosomes and the nuclear envelope fragments into vesicles filled with nucleosomal components. Pyknotic nuclei and vacuolated cytoplasm often histologically distinguish this regimented apoptosis process. Casciola-Rosen et al. [81] demonstrated that in the course of death through apoptosis, cells translocate the SLE autoantigens from the nuclear compartment to the cell surface, displaying them to the extracellular environment in membranous blebs called apoptotic bodies. The physiological display of nuclear antigens in apoptotic bodies offers a plausible mechanism whereby the SLE prominent autoantigens are exposed to the immune system, yielding the possibility of stimulating an autoimmune response.

As another explanation, a recent report by DeGiorgio et al. [83] provided evidence that a subset of anti-DNA antibodies cross-reacts with the glutamate receptor subtype NMDA (N-methyl-D-aspartate) and induces neuronal cell injury. These data argue towards a concept that anti-DNA antibodies cross-react with self-antigens, which would elicit tissue damage. However, it was not directly shown that this autoantibody is responsible for the central nervous system damage seen in SLE patients. In addition, it would also be important to identify target antigens expressed in other organs that are recognized by anti-dsDNA antibodies.

Therapeutic contribution of removal or alteration of nucleosomal antigens
Macanovic et al. [84] have reported that recombinant DNase I reduces the autoimmune response in lupus-susceptible mice. However, human clinical trials of recombinant DNase I for SLE did not show significant improvement of SLE symptoms [85]. Our studies show that only two SLE patients out of 100 have the DNase I mutation (Yasutomo et al., unpublished observation). Thus, it is important to check the efficacy of recombinant DNase I for SLE patients with the DNase I mutation. Furthermore, T and B cells have several specificities against non-nucleosomal antigens at advanced disease stages even if the nucleosomal antigen-specific lymphocyte is a disease trigger. Therefore, recombinant DNase I treatment may have a benefit only during early SLE disease stages.

Regarding the therapeutic contribution of nucleosomal antigens, Lu et al. [86] reported that CD4+ T cells from lupus patients responded strongly to certain histone peptides (H2B10–33, H416–39, H471–94, H391–105, H2A34–48 and H449–63). These same peptides overlap with major epitopes for helper CD4+ T cells that induce anti-DNA autoantibodies and nephritis in lupus mice. There is much evidence that the altered peptide ligands induce anergy in T cells [8789]. Based on these results, Datta et al. [90] tried to inhibit murine lupus by using altered histone peptides and were able to inhibit partially the murine SLE-like syndrome. Each peptide found in human SLE has different abilities for T-cell proliferation or cytokine secretion profiles, which suggests that each epitope plays a specific role for inducing or suppressing the autoimmune T-cell response. Thus, caution should be used when applying this technique in the clinic because it would be dangerous to inhibit T-cell responses that are inhibiting SLE. Furthermore, human HLA variations make it difficult to find altered ligands in each SLE patient. In order to overcome these problems, it is essential to establish a therapeutic strategy that can be applied to all SLE patients.


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Based on mutations in autoimmune mouse models, several candidate genes related to human systemic autoimmune diseases have been reported. One example is the defective Fas/Fas ligand genes in autoimmune lymphoproliferative syndrome (ALPS) [23, 25, 91]. ALPS patients develop SLE-like autoimmune symptoms with massive lymphoproliferation early in life. However, ALPS clinical features are quite different from those of SLE. We now know that the targeted mutation of many genes or even lymphocytes themselves can cause the SLE-like syndrome in mice. However, the corresponding human gene mutation(s) in SLE is still unknown. Of course, we should examine the entire region, including the 5' and 3' flanking non-coding regions, of such genes in the future. On the other hand, according to recent studies, genes that are associated with antigen clearance contribute to SLE development or progression in mouse and human models. Perhaps we should direct the focus of the gene search from signalling molecules to antigen clearance molecules. We are now intensively investigating such candidate genes.


    Acknowledgments
 
I would like to thank Dr Horiuch for the DNase I mutation collaboration.


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  1. Davidson A, Diamond B. Autoimmune diseases. N Engl J Med 2001;345:340–50.[Free Full Text]
  2. Marrack P, Kappler J, Kotzin BL. Autoimmune disease: why and where it occurs. Nat Med 2001;7:899–905.[CrossRef][ISI][Medline]
  3. Santamaria P. Effector lymphocytes in autoimmunity. Curr Opin Immunol 2001;13:663–9.[CrossRef][ISI][Medline]
  4. Haneji N, Nakamura T, Takio K et al. Identification of alpha-fodrin as a candidate autoantigen in primary Sjögren's syndrome. Science 1997;276:604–7.[Abstract/Free Full Text]
  5. Elson CJ, Barker RN. Helper T cells in antibody-mediated, organ-specific autoimmunity. Curr Opin Immunol 2000;12:664–9.[CrossRef][ISI][Medline]
  6. Hayashi Y, Haneji N, Hamano H, Yanagi K. Transfer of Sjögren's syndrome-like autoimmune lesions into SCID mice and prevention of lesions by anti-CD4 and anti-T cell receptor antibody treatment. Eur J Immunol 1994;24:2826–31.[ISI][Medline]
  7. Oono T, Fukui Y, Masuko S et al. Organ-specific autoimmunity in mice whose T cell repertoire is shaped by a single antigenic peptide. J Clin Invest 2001;108:1589–96.[Abstract/Free Full Text]
  8. Wakeland EK, Liu K, Graham RR, Behrens TW. Delineating the genetic basis of systemic lupus erythematosus. Immunity 2001;15:397–408.[ISI][Medline]
  9. Vyse TJ, Todd JA. Genetic analysis of autoimmune disease. Cell 1996;85:311–8.[ISI][Medline]
  10. Takeno M, Nagafuchi H, Kaneko S et al. Autoreactive T cell clones from patients with systemic lupus erythematosus support polyclonal autoantibody production. J Immunol 1997;158:3529–38.[Abstract]
  11. Shull MM, Ormsby I, Kier AB et al. Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. Nature 1992;359:693–9.[CrossRef][ISI][Medline]
  12. Tivol EA, Borriello F, Schweitzer AN, Lynch WP, Bluestone JA, Sharpe AH. Loss of CTLA-4 leads to massive lymphoproliferation and fatal multiorgan tissue destruction, revealing a critical negative regulatory role of CTLA-4. Immunity 1995;3:541–7.[ISI][Medline]
  13. Nishimura H, Nose M, Hiai H, Minato N, Honjo T. Development of lupus-like autoimmune diseases by disruption of the PD-1 gene encoding an ITIM motif-carrying immunoreceptor. Immunity 1999;11:141–51.[ISI][Medline]
  14. O'Keefe TL, Williams GT, Davies SL, Neuberger MS. Hyperresponsive B cells in CD22-deficient mice. Science 1996;274:798–801.[Abstract/Free Full Text]
  15. Hibbs ML, Tarlinton DM, Armes J et al. Multiple defects in the immune system of Lyn-deficient mice, culminating in autoimmune disease. Cell 1995;83:301–11.[ISI][Medline]
  16. Tsui HW, Siminovitch KA, de Souza L, Tsui FW. Motheaten and viable motheaten mice have mutations in the haematopoietic cell phosphatase gene. Nat Genet 1993;4:124–9.[ISI][Medline]
  17. Taylor GA, Carballo E, Lee DM et al. A pathogenetic role for TNF alpha in the syndrome of cachexia, arthritis, and autoimmunity resulting from tristetraprolin (TTP) deficiency. Immunity 1996;4:445–54.[ISI][Medline]
  18. Brunkow ME, Jeffery EW, Hjerrild KA et al. Disruption of a new forkhead/winged-helix protein, scurfin, results in the fatal lymphoproliferative disorder of the scurfy mouse. Nat Genet 2001;27:68–73.[CrossRef][ISI][Medline]
  19. Majeti R, Xu Z, Parslow TG et al. An inactivating point mutation in the inhibitory wedge of CD45 causes lymphoproliferation and autoimmunity. Cell 2000;103:1059–70.[ISI][Medline]
  20. Chiang YJ, Kole HK, Brown K et al. Cbl-b regulates the CD28 dependence of T-cell activation. Nature 2000;403:216–20.[CrossRef][ISI][Medline]
  21. Bachmaier K, Krawczyk C, Kozieradzki I et al. Negative regulation of lymphocyte activation and autoimmunity by the molecular adaptor Cbl-b. Nature 2000;403:211–6.[CrossRef][ISI][Medline]
  22. Watanabe-Fukunaga R, Brannan CI, Copeland NG, Jenkins NA, Nagata S. Lymphoproliferation disorder in mice explained by defects in Fas antigen that mediates apoptosis. Nature 1992;356:314–7.[CrossRef][ISI][Medline]
  23. Fisher GH, Rosenberg FJ, Straus SE et al. Dominant interfering Fas gene mutations impair apoptosis in a human autoimmune lymphoproliferative syndrome. Cell 1995;81:935–46.[ISI][Medline]
  24. Takahashi T, Tanaka M, Brannan CI et al. Generalized lymphoproliferative disease in mice, caused by a point mutation in the Fas ligand. Cell 1994;76:969–76.[ISI][Medline]
  25. Wu J, Wilson J, He J, Xiang L, Schur PH, Mountz JD. Fas ligand mutation in a patient with systemic lupus erythematosus and lymphoproliferative disease. J Clin Invest 1996;98:1107–13.[Abstract/Free Full Text]
  26. Balomenos D, Martin-Caballero J, Garcia MI et al. The cell cycle inhibitor p21 controls T-cell proliferation and sex-linked lupus development. Nat Med 2000;6:171–6.[CrossRef][ISI][Medline]
  27. Wang J, Zheng L, Lobito A et al. Inherited human Caspase 10 mutations underlie defective lymphocyte and dendritic cell apoptosis in autoimmune lymphoproliferative syndrome type II. Cell 1999;98:47–58.[ISI][Medline]
  28. Scott RS, McMahon EJ, Pop SM et al. Phagocytosis and clearance of apoptotic cells is mediated by MER. Nature 2001;411:207–11.[CrossRef][ISI][Medline]
  29. Botto M, Dell'Agnola C, Bygrave AE et al. Homozygous C1q deficiency causes glomerulonephritis associated with multiple apoptotic bodies. Nat Genet 1998;19:56–9.[ISI][Medline]
  30. Kirschfink M, Petry F, Khirwadkar K, Wigand R, Kaltwasser JP, Loos M. Complete functional C1q deficiency associated with systemic lupus erythematosus (SLE). Clin Exp Immunol 1993;94:267–72.[ISI][Medline]
  31. Bickerstaff MC, Botto M, Hutchinson WL et al. Serum amyloid P component controls chromatin degradation and prevents antinuclear autoimmunity. Nat Med 1999;5:694–7.[CrossRef][ISI][Medline]
  32. Boes M, Schmidt T, Linkemann K, Beaudette BC, Marshak-Rothstein A, Chen J. Accelerated development of IgG autoantibodies and autoimmune disease in the absence of secreted IgM. Proc Natl Acad Sci USA 2000;97:1184–9.[Abstract/Free Full Text]
  33. Napirei M, Karsunky H, Zevnik B, Stephan H, Mannherz HG, Moroy T. Features of systemic lupus erythematosus in DNaseI-deficient mice. Nat Genet 2000;25:177–81.[CrossRef][ISI][Medline]
  34. Yasutomo K, Horiuchi T, Kagami S et al. Mutation of DNASE1 in people with systemic lupus erythematosus. Nat Genet 2001;28:313–4.[CrossRef][ISI][Medline]
  35. Le LQ, Kabarowski JH, Weng Z et al. Mice lacking the orphan G protein-coupled receptor G2A develop a late-onset autoimmune syndrome. Immunity 2001;14:561–71.[CrossRef][ISI][Medline]
  36. Chui D, Sellakumar G, Green R et al. Genetic remodeling of protein glycosylation in vivo induces autoimmune disease. Proc Natl Acad Sci USA 2001;98:1142–7.[Abstract/Free Full Text]
  37. Demetriou M, Granovsky M, Quaggin S, Dennis JW. Negative regulation of T-cell activation and autoimmunity by Mgat5 N-glycosylation. Nature 2001;409:733–9.[CrossRef][ISI][Medline]
  38. Rozzo SJ, Allard JD, Choubey D et al. Evidence for an interferon-inducible gene, Ifi202, in the susceptibility to systemic lupus. Immunity 2001;15:435–43.[ISI][Medline]
  39. Viret C, Wong FS, Janeway CA, Jr. Designing and maintaining the mature TCR repertoire: the continuum of self-peptide:self-MHC complex recognition. Immunity 1999;10:559–68.[ISI][Medline]
  40. Surh CD, Sprent J. Homeostatic T cell proliferation: how far can T cells be activated to self-ligands? J Exp Med 2000;192:F9–14.[ISI][Medline]
  41. Marrack P, Bender J, Hildeman D et al. Homeostasis of alpha beta TCR+ T cells. Nat Immunol 2000;1:107–11.[CrossRef][ISI][Medline]
  42. Dorfman JR, Stefanova I, Yasutomo K, Germain RN. CD4+ T cell survival is not directly linked to self-MHC-induced TCR signaling. Nat Immunol 2000;1:329–35.[CrossRef][ISI][Medline]
  43. Liossis SN, Kovacs B, Dennis G, Kammer GM, Tsokos GC. B cells from patients with systemic lupus erythematosus display abnormal antigen receptor-mediated early signal transduction events. J Clin Invest 1996;98:2549–57.[Abstract/Free Full Text]
  44. Liossis SN, Ding XZ, Dennis GJ, Tsokos GC. Altered pattern of TCR/CD3-mediated protein-tyrosyl phosphorylation in T cells from patients with systemic lupus erythematosus. Deficient expression of the T cell receptor zeta chain. J Clin Invest 1998;101:1448–57.[Abstract/Free Full Text]
  45. Yablonski D, Weiss A. Mechanisms of signaling by the hematopoietic-specific adaptor proteins, SLP-76 and LAT and their B cell counterpart, BLNK/SLP-65. Adv Immunol 2001;79:93–128.[CrossRef][ISI][Medline]
  46. Weiss A, Littman DR. Signal transduction by lymphocyte antigen receptors. Cell 1994;76:263–74.[ISI][Medline]
  47. Lanzavecchia A, Lezzi G, Viola A. From TCR engagement to T cell activation: a kinetic view of T cell behavior. Cell 1999;96:1–4.[ISI][Medline]
  48. Germain RN. The T cell receptor for antigen: signaling and ligand discrimination. J Biol Chem 2001;276:35223–6.[Free Full Text]
  49. Chambers CA, Allison JP. Costimulatory regulation of T cell function. Curr Opin Cell Biol 1999;11:203–10.[CrossRef][ISI][Medline]
  50. Vassilopoulos D, Kovacs B, Tsokos GC. TCR/CD3 complex-mediated signal transduction pathway in T cells and T cell lines from patients with systemic lupus erythematosus. J Immunol 1995;155:2269–81.[Abstract]
  51. Filaci G, Bacilieri S, Fravega M et al. Impairment of CD8+ T suppressor cell function in patients with active systemic lupus erythematosus. J Immunol 2001;166:6452–7.[Abstract/Free Full Text]
  52. Shevach EM, McHugh RS, Piccirillo CA, Thornton AM. Control of T-cell activation by CD4+ CD25+ suppressor T cells. Immunol Rev 2001;182:58–67.[CrossRef][ISI][Medline]
  53. Jensen WA, Pleiman CM, Beaufils P, Wegener AM, Malissen B, Cambier JC. Qualitatively distinct signaling through T cell antigen receptor subunits. Eur J Immunol 1997;27:707–16.[ISI][Medline]
  54. Love PE, Shores EW, Johnson MD et al. T cell development in mice that lack the zeta chain of the T cell antigen receptor complex. Science 1993;261:918–21.[ISI][Medline]
  55. Shores EW, Huang K, Tran T, Lee E, Grinberg A, Love PE. Role of TCR zeta chain in T cell development and selection. Science 1994;266:1047–50.[ISI][Medline]
  56. Nambiar MP, Enyedy EJ, Warke VG et al. Polymorphisms/mutations of TCR-zeta-chain promoter and 3' untranslated region and selective expression of TCR zeta-chain with an alternatively spliced 3' untranslated region in patients with systemic lupus erythematosus. J Autoimmun 2001;16:133–42.[CrossRef][ISI][Medline]
  57. Krop I, Shaffer AL, Fearon DT, Schlissel MS. The signaling activity of murine CD19 is regulated during cell development. J Immunol 1996;157:48–56.[Abstract]
  58. Sato S, Ono N, Steeber DA, Pisetsky DS, Tedder TF. CD19 regulates B lymphocyte signaling thresholds critical for the development of B-1 lineage cells and autoimmunity. J Immunol 1996;157:4371–8.[Abstract]
  59. Zhou LJ, Smith HM, Waldschmidt TJ, Schwarting R, Daley J, Tedder TF. Tissue-specific expression of the human CD19 gene in transgenic mice inhibits antigen-independent B-lymphocyte development. Mol Cell Biol 1994;14:3884–94.[Abstract]
  60. Sato S, Miller AS, Howard MC, Tedder TF. Regulation of B lymphocyte development and activation by the CD19/CD21/CD81/Leu 13 complex requires the cytoplasmic domain of CD19. J Immunol 1997;159:3278–87.[Abstract]
  61. Tedder TF, Inaoki M, Sato S. The CD19-CD21 complex regulates signal transduction thresholds governing humoral immunity and autoimmunity. Immunity 1997;6:107–18.[ISI][Medline]
  62. Fujimoto M, Fujimoto Y, Poe JC et al. CD19 regulates Src family protein tyrosine kinase activation in B lymphocytes through processive amplification. Immunity 2000;13:47–57.[ISI][Medline]
  63. Fujimoto M, Bradney AP, Poe JC, Steeber DA, Tedder TF. Modulation of B lymphocyte antigen receptor signal transduction by a CD19/CD22 regulatory loop. Immunity 1999;11:191–200.[ISI][Medline]
  64. Sebzda E, Mariathasan S, Ohteki T, Jones R, Bachmann MF, Ohashi PS. Selection of the T cell repertoire. Annu Rev Immunol 1999;17:829–74.[CrossRef][ISI][Medline]
  65. Saito T, Watanabe N. Positive and negative thymocyte selection. Crit Rev Immunol 1998;18:359–70.[ISI][Medline]
  66. Clarke SR, Rudensky AY. Survival and homeostatic proliferation of naive peripheral CD4+ T cells in the absence of self peptide:MHC complexes. J Immunol 2000;165:2458–64.[Abstract/Free Full Text]
  67. Murali-Krishna K, Lau LL, Sambhara S, Lemonnier F, Altman J, Ahmed R. Persistence of memory CD8 T cells in MHC class I-deficient mice. Science 1999;286:1377–81.[Abstract/Free Full Text]
  68. Goldrath AW, Bogatzki LY, Bevan MJ. Naive T cells transiently acquire a memory-like phenotype during homeostasis-driven proliferation. J Exp Med 2000;192:557–64.[Abstract/Free Full Text]
  69. Murali-Krishna K, Ahmed R. Cutting edge: naive T cells masquerading as memory cells. J Immunol 2000;165:1733–7.[Abstract/Free Full Text]
  70. Cho BK, Rao VP, Ge Q, Eisen HN, Chen J. Homeostasis-stimulated proliferation drives naive T cells to differentiate directly into memory T cells. J Exp Med 2000;192:549–56.[Abstract/Free Full Text]
  71. Sabzevari H, Propp S, Kono DH, Theofilopoulos AN. G1 arrest and high expression of cyclin kinase and apoptosis inhibitors in accumulated activated/memory phenotype CD4+ cells of older lupus mice. Eur J Immunol 1997;27:1901–10.[ISI][Medline]
  72. Yasutomo K, Doyle C, Miele L, Fuchs C, Germain RN. The duration of antigen receptor signalling determines CD4+ versus CD8+ T-cell lineage fate. Nature 2000;404:506–10.[CrossRef][ISI][Medline]
  73. Iezzi G, Karjalainen K, Lanzavecchia A. The duration of antigenic stimulation determines the fate of naive and effector T cells. Immunity 1998;8:89–95.[ISI][Medline]
  74. Germain RN. The art of the probable: system control in the adaptive immune system. Science 2001;293:240–5.[Abstract/Free Full Text]
  75. Tan EM, Cohen AS, Fries JF et al. The 1982 revised criteria for the classification of systemic lupus erythematosus. Arthritis Rheum 1982;25:1271–7.[ISI][Medline]
  76. Chitrabamrung S, Rubin RL, Tan EM. Serum deoxyribonuclease I and clinical activity in systemic lupus erythematosus. Rheumatol Int 1981;1:55–60.[ISI][Medline]
  77. Tew MB, Johnson RW, Reveille JD, Tan FK. A molecular analysis of the low serum deoxyribonuclease activity in lupus patients. Arthritis Rheum 2001;44:2446–7.[CrossRef][ISI][Medline]
  78. Pan CQ, Dodge TH, Baker DL, Prince WS, Sinicropi DV, Lazarus RA. Improved potency of hyperactive and actin-resistant human DNase I variants for treatment of cystic fibrosis and systemic lupus erythematosus. J Biol Chem 1998;273:18374–81.[Abstract/Free Full Text]
  79. Amoura Z, Piette JC, Chabre H et al. Circulating plasma levels of nucleosomes in patients with systemic lupus erythematosus: correlation with serum antinucleosome antibody titers and absence of clear association with disease activity. Arthritis Rheum 1997;40:2217–25.[ISI][Medline]
  80. Mevorach D, Zhou JL, Song X, Elkon KB. Systemic exposure to irradiated apoptotic cells induces autoantibody production. J Exp Med 1998;188:387–92.[Abstract/Free Full Text]
  81. Casciola-Rosen LA, Anhalt G, Rosen A. Autoantigens targeted in systemic lupus erythematosus are clustered in two populations of surface structures on apoptotic keratinocytes. J Exp Med 1994;179:1317–30.[Abstract]
  82. Mevorach D, Mascarenhas JO, Gershov D, Elkon KB. Complement-dependent clearance of apoptotic cells by human macrophages. J Exp Med 1998;188:2313–20.[Abstract/Free Full Text]
  83. DeGiorgio LA, Konstantinov KN, Lee SC, Hardin JA, Volpe BT, Diamond B. A subset of lupus anti-DNA antibodies cross-reacts with the NR2 glutamate receptor in systemic lupus erythematosus. Nat Med 2001;7:1189–93.[CrossRef][ISI][Medline]
  84. Macanovic M, Sinicropi D, Shak S, Baughman S, Thiru S, Lachmann PJ. The treatment of systemic lupus erythematosus (SLE) in NZB/W F1 hybrid mice; studies with recombinant murine DNase and with dexamethasone. Clin Exp Immunol 1996;106:243–52.[ISI][Medline]
  85. Davis JC Jr, Manzi S, Yarboro C et al. Recombinant human DNase I (rhDNase) in patients with lupus nephritis. Lupus 1999;8:68–76.[ISI][Medline]
  86. Lu L, Kaliyaperumal A, Boumpas DT, Datta SK. Major peptide autoepitopes for nucleosome-specific T cells of human lupus. J Clin Invest 1999;104:345–55.[Abstract/Free Full Text]
  87. Sloan-Lancaster J, Evavold BD, Allen PM. Induction of T-cell anergy by altered T-cell-receptor ligand on live antigen-presenting cells. Nature 1993;363:156–9.[CrossRef][ISI][Medline]
  88. Sloan-Lancaster J, Evavold BD, Allen PM. Th2 cell clonal anergy as a consequence of partial activation. J Exp Med 1994;180:1195–205.[Abstract]
  89. Ryan KR, Evavold BD. Persistence of peptide-induced CD4+ T cell anergy in vitro. J Exp Med 1998;187:89–96.[Abstract/Free Full Text]
  90. Kaliyaperumal A, Michaels MA, Datta SK. Antigen-specific therapy of murine lupus nephritis using nucleosomal peptides: tolerance spreading impairs pathogenic function of autoimmune T and B cells. J Immunol 1999;162:5775–83.[Abstract/Free Full Text]
  91. Rieux-Laucat F, Le Deist F, Hivroz C et al. Mutations in Fas associated with human lymphoproliferative syndrome and autoimmunity. Science 1995;268:1347–9.[ISI][Medline]
Submitted 30 April 2002; Accepted 2 August 2002





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