Lessons from the NZM2410 model and related strains

Animal models of systemic lupus erythematosus and their applications in drug discovery

INTRODUCTION

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with substantial phenotypic heterogeneity. Currently, our understanding of the pathogenesis is still limited, and as a result, specific and efficacious therapies are lacking. Various mouse models have been established to serve as powerful tools that will promote a better understanding of the disease and the ability to test novel drugs before clinical application.

AREAS COVERED

The authors review the existing mouse models of SLE in terms of pathogenesis and manifestations, as well as their applications in drug discovery and development. The areas of focus include promising novel therapeutics that could benefit patients in the future and the contribution of mouse models used in preclinical studies.

EXPERT OPINION

Given the diversity of SLE mouse models with different characteristics, researchers must select a suitable model based on the mechanism involved. The use of multiple models is needed for drug testing studies to evaluate drug efficacy on different genetic backgrounds and other mechanisms to provide a reference for clinical trials.

TLR7 Agonism Accelerates Disease and Causes a Fatal Myeloproliferative Disorder in NZM 2410 Lupus Mice

Murine models of lupus, both spontaneous and inducible, are valuable instruments to study SLE pathogenesis. Accelerants such as Type I IFN are often used to trigger earlier disease onset. We used a topical TLR7 agonist, previously reported to induce lupus-like disease in WT mice within weeks, to validate this data in C57BL/6j mice, and to test TLR7 agonism as an accelerant in lupus-prone NZM2410 mice. We found that TLR7-stimulated B6 and NZM2410 mice had significantly reduced survival and exhibited profound splenomegaly with significantly reduced B cells (4 vs. 40%), and T cells (8 vs. 31%). Spleen pathology and IHC revealed massive expansion of F4/80+ cells in TLR7-treated mice consistent with histiocytosis. While resiqimod treatment caused mild autoimmunity in B6 mice and accelerated autoimmunity in NZM2410 mice, it did not cause significant nephritis or proteinuria in either strain (renal function intact at death). Given the macrophage expansion, cytopenias, and disruption of normal splenic lymphoid follicle architecture, histiocytic sarcoma is favored as the cause of death. An alternative etiology is a macrophage activation syndrome (MAS)-like syndrome, since the mice also had a transaminitis and histologic hemophagocytosis in the setting of their rapid mortality. For investigators who are focused on murine models of lupus nephritis, this model is not ideal when utilizing B6 mice, however topical resiqimod may prove useful to accelerate autoimmunity and nephritis in NZM2410 mice, or potentially to investigate secondary complications of lupus such as histiocytic diseases or macrophage activation like syndromes.

The Complex Association of FcγRIIb With Autoimmune Susceptibility

FcγRIIb is the only inhibitory Fc receptor and controls many aspects of immune and inflammatory responses. The observation 19 years ago that Fc γ RIIb ^-/- mice generated by gene targeting in 129 derived ES cells developed severe lupus like disease when backcrossed more than 7 generations into C57BL/6 background initiated extensive research on the functional understanding of this strong autoimmune phenotype. The genomic region in the distal part of Chr1 both in human and mice in which the Fc γ R gene cluster is located shows a high level of complexity in relation to the susceptibility to SLE. Specific haplotypes of closely linked genes including the Fc γ RIIb and Slamf genes are associated with increased susceptibility to SLE both in mice and human. Using forward and reverse genetic approaches including in human GWAS and in mice congenic strains, KO mice (germline and cell type specific, on different genetic background), knockin mice, overexpressing transgenic mice combined with immunological models such as adoptive transfer of B cells from Ig transgenic mice the involved genes and the causal mutations and their associated functional alterations were analyzed. In this review the results of this 19 years extensive research are discussed with a focus on (genetically modified) mouse models.

Selenium supplementation suppresses immunological and serological features of lupus in B6.Sle1b mice

Systemic lupus erythematosus (SLE) is a debilitating multi-factorial immunological disorder characterized by increased inflammation and development of anti-nuclear autoantibodies. Selenium (Se) is an essential trace element with beneficial anti-cancer and anti-inflammatory immunological functions. In our previous proteomics study, analysis of Se-responsive markers in the circulation of Se-supplemented healthy men showed a significant increase in complement proteins. Additionally, Se supplementation prolonged the life span of lupus prone NZB/NZW-F1 mice. To better understand the protective immunological role of Se in SLE pathogenesis, we have investigated the impact of Se on B cells and macrophages using in vitro Se supplementation assays and the B6.Sle1b mouse model of lupus with an oral Se or placebo supplementation regimen. Analysis of Se-treated B6.Sle1b mice showed reduced splenomegaly and splenic cellularity compared to untreated B6. Sle1b mice. A significant reduction in total B cells and notably germinal center (GC) B cell numbers was observed. However, other cell types including T cells, Tregs, DCs and pDCs were unaffected. Consistent with reduced GC B cells there was a significant reduction in autoantibodies to dsDNA and SmRNP of the IgG2b and IgG2c subclass upon Se supplementation. We found that increased Se availability leads to impaired differentiation and maturation of macrophages from mouse bone marrow derived progenitors in vitro. Additionally, Se treatment during in vitro activation of B cells with anti-CD40L and LPS inhibited optimal B cell activation. Overall our data indicate that Se supplementation inhibits activation, differentiation and maturation of B cells and macrophages. Its specific inhibitory effect on B cell activation and GC B cell differentiation could be explored as a potential therapeutic supplement for SLE patients.

Complete knockout of estrogen receptor alpha is not directly protective in murine lupus

Systemic lupus erythematosus (SLE) is a chronic and potentially severe autoimmune disease that disproportionately affects women. Despite a known role for hormonal factors impacting autoimmunity and disease pathogenesis, the specific mechanisms of action remain poorly understood. Our laboratory previously backcrossed "estrogen receptor alpha knockout (ERαKO)" mice onto the NZM2410 lupus prone background to generate NZM/ERαKO mice. This original ERαKO mouse, developed in the mid-1990s and utilized in hundreds of published studies, is not in fact ERα null. They express an N-terminally truncated ERα, and are considered a functional KO. They have physiologic deficiencies including infertility due to disruption of a critical activation domain (AF-1) at the N terminus of ERα, required for most classic estrogen (E2) actions. We demonstrated that female NZM/ERαKO mice had significantly less renal disease and significantly prolonged survival compared to WT littermates despite similar serum levels of autoantibodies and glomerular immune complex deposition. Herein, we present results of experiments using a lupus prone true ERα-/- mice (deletional KO mice on the NZM2410 background), surprisingly finding that these animals were not protected if they were ovariectomized, suggesting that another hormonal component confers protection, possibly testosterone, rather than the absence of the full-length ERα.

VISTA Deficiency Accelerates the Development of Fatal Murine Lupus Nephritis

OBJECTIVE

The targeting of negative checkpoint regulators as a means of augmenting antitumor immune responses is now an increasingly used and remarkably effective approach to the treatment of several human malignancies. The negative checkpoint regulator VISTA (V-domain Ig-containing suppressor of T cell activation; also known as programmed death 1 homolog or as death domain 1α) suppresses T cell responses and regulates myeloid activities. We proposed that exploitation of the VISTA pathway is a novel strategy for the treatment of human autoimmune disease, and therefore we undertook this study to determine the impact of VISTA genetic deficiency on lupus development in a lupus-prone mouse strain.

METHODS

To evaluate whether genetic deficiency of VISTA affects the development of lupus, we interbred VISTA-deficient mice with Sle1.Sle3 mice, a well-characterized model of systemic lupus erythematosus (SLE).

RESULTS

We demonstrated that the development of proteinuria and glomerulonephritis in these mice, designated Sle1.Sle3 VISTA^-/- mice, was greatly accelerated and more severe compared to that in Sle1.Sle3 and C57BL/6 VISTA^-/- mice. Analysis of cells from Sle1.Sle3 VISTA^-/- mice showed enhanced activation of splenic CD4+ T cells and myeloid cell populations. No increase in titers of autoantibodies was seen in Sle1.Sle3 VISTA^-/- mice. Most striking was a significant increase in proinflammatory cytokines, chemokines, and interferon (IFN)-regulated genes associated with SLE, such as IFNα, IFNγ, tumor necrosis factor, interleukin-10, and CXCL10, in Sle1.Sle3 VISTA^-/- mice.

CONCLUSION

This study demonstrates for the first time that loss of VISTA in murine SLE exacerbates disease due to enhanced myeloid and T cell activation and cytokine production, including a robust IFNα signature, and supports a strategy of enhancement of the immunosuppressive activity of VISTA for the treatment of human lupus.

Autoimmune-mediated glucose intolerance in a mouse model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies against self-antigens such as double-stranded DNA and phospholipids. Classical comorbidities of SLE include glomerulonephritis, infection, cardiovascular disease, arthritis, skin disorders, and neurological disease. In addition to these classical comorbidities, there is emerging evidence that SLE patients are at higher risk of developing insulin resistance and other components of the metabolic syndrome. Visceral adipose tissue inflammation is a central mediator of insulin resistance in the obese setting, but the mechanism behind the pathogenesis of metabolic disease in the SLE patient population is unclear. We hypothesize that lupus-associated changes in the adaptive immune system are associated with disruption in glucose homeostasis in the context of SLE. To test this hypothesis, we assessed the metabolic and immunological phenotype of SLE-prone B6.SLE mice. B6.SLE mice fed a low-fat diet had significantly worsened glucose tolerance, increased adipose tissue insulin resistance, increased β-cell insulin secretion, and increased adipocyte size compared with their respective B6 controls. Independently of diet, B cells isolated from the white adipose tissue of B6.SLE mice were skewed toward IgG production, and the level of IgG1 was elevated in the serum of SLE-prone mice. These data show that B6.SLE mice develop defects in glucose homeostasis even when fed a low-fat diet and suggest that B cells may play a role in this metabolic dysfunction.

The lupus-prone NZM2410/NZW strain-derived Sle1b sublocus alters the germinal center checkpoint in female mice in a B cell-intrinsic manner

C57BL/6 (B6) mice carrying the Sle1b sublocus (named B6.Sle1b), which harbors the lupus-associated NZM2410/NZW SLAM family genes, produce antinuclear Abs (ANAs). However, the role and mechanism(s) involved in the alteration of the germinal center (GC) tolerance checkpoint in the development of ANAs in these mice is not defined. In this study, we show significantly higher spontaneously formed GCs (Spt-GCs) in B6.Sle1b female mice compared with B6 controls. We also found a significant increase in CD4(+)CXCR5(hi)PD-1(hi) spontaneously activated follicular Th cells in B6.Sle1b female mice. Compared with B6 controls, B6.Sle1b female mice had increased numbers of proliferating B cells predominantly located in Spt-GCs. The elevated Spt-GCs in B6.Sle1b female mice were strongly associated with increased ANA-specific Ab-forming cells and ANA titers. The increased numbers of Spt-GCs and spontaneously activated follicular Th cells in B6.Sle1b mice were not the result of a generalized defect in B cells expressing Sle1b. Consistent with the elevated spontaneous response in B6.Sle1b mice, the attenuated GC response characteristic of DNA and p-azophenylarsonate reactive B cells from Ig V(H) knock-in mice (termed HKIR) were relieved in adoptively transferred recipients in the presence of Sle1b. Finally, by generating mixed bone marrow chimeras, we showed that the effect of Sle1b on Spt-GC, follicular Th cell, and autoantibody responses in B6.Sle1b mice was B cell autonomous. These data indicate that the NZM2410/NZW-derived Sle1b sublocus in conjunction with the female sex primarily affects B cells, leading to the alteration of the GC tolerance checkpoint and the generation of ANA-specific Ab-forming cells.

The role of NK cells in the development of autoantibodies

The systemic lupus erythematosus (Sle1) interval from the NZM2410 mouse strain has been shown to be responsible for high levels of autoantibody production against antinuclear antibodies (ANA) when transferred into C57BL/6 mice. B cells derived from the B6.Sle1 strain are required for the production but help from both T-dependent and independent sources have been documented. Using radiation chimeras constructed in a strain of mice that is chronically depleted of Natural killer (NK) cells, but not NKT cells, we have examined the role of NK cells in the development of ANA in this context. Our results show that in the presence of intact T cell help depletion of NK cells does not affect ANA production. However, when T cell help is compromised, the prevalence of animals producing ANA is significantly decreased suggesting that NK cells can provide help for the T-independent production of ANA. Further experiments provide a possible mechanism for the NK-cell dependence.

Poly(ADP-ribose) polymerase-1 regulates the progression of autoimmune nephritis in males by inducing necrotic cell death and modulating inflammation

Necrotic lesions and necrotic cell death characterize severe autoimmune nephritides, and contribute to local inflammation and to progression of the disease. Poly(ADP-ribose) polymerase-1 (PARP-1), a DNA repair enzyme, is involved in the induction of necrosis and is a key player in the acute and chronic inflammation. Therefore, we hypothesized that PARP-1 controls the severity of nephritis by mediating the induction of necrosis in the kidney. We used lupus and anti-glomerular basement membrane models of nephritis to determine the effects of PARP-1 on the inflammatory response in the kidney. We show in this study that PARP-1 is indeed activated during the course of glomerulonephritis. We also show that the absence of PARP-1 or its pharmacological inhibition results in milder nephritis, with lower blood urea nitrogen levels, reduced necrotic lesions, and higher survival rates. The relevance of PARP-1 showed a strong male sex specificity, and treatment of male mice with 17beta-estradiol prolonged their survival during the course of nephritis. PARP-1 also regulated TNF-alpha expression and up-regulation of adhesion molecules, further supporting a role of PARP-1 in the inflammatory process within the kidney. Our results demonstrate that PARP-1 activation and consequent necrotic cell death play an important role in the pathogenesis of male nephritis, and suggest that PARP-1 can be a novel therapeutic target in glomerulonephritis.

Fc receptor genes and the systemic lupus erythematosus diathesis

Fc receptors represent a distinct group of hematopoeitic cell surface glycoproteins that have a characterized role in affecting the efficiency of the mononuclear phagocyte system to clear IgG immune complexes. Functional genetic variations in this family of receptors have been identified as heritable susceptibility factors for SLE and lupus nephritis across diverse populations. In this review, we describe the roles of the classical Fc receptors for IgG (Fc gamma) and non-classical Fc-like receptors (FCR1-FCRL6L), Fc receptors for IgE (Fc epsilon RI) and IgA and IgM (Fc alpha/mu R) in SLE diathesis. The combined effects of these genes on SLE pathogenesis, either via linkage disequilibrium or epistasis with additional genetic or environmental factors, provide a challenge for future investigations. The pursuit of a polygenic SLE-profile that includes longitudinal evaluations of SLE and markers involved in the protean clinical manifestations associated with SLE will facilitate our understanding of the cascade of inflammatory events associated with the diathesis.

SLE 1, 2, 3...genetic dissection of lupus

Systemic lupus erythematosus (SLE) is a chronic and complex autoimmune disease of unknown etiology, characterized by the presence of widespread immunological abnormalities and multiorgan injury. An important advance over the past decade has been our understanding of how different genetic loci (or genes) may dictate specific immune abnormalities in lupus. "Genetic dissection" has unveiled some of the mystery enshrouding lupus pathogenesis. It appears that there are at least two distinct events leading to disease. The first involves a breach in the adaptive immune system and the second involves a dysregulation of innate immunity. Co-ordinate dysregulation of both checkpoints is necessary for full-blown lupus to ensue. The challenge ahead is to understand how these two checkpoints are regulated in human SLE, and to devise therapeutic strategies that target both checkpoints.

The lupus-susceptibility locus, Sle3, mediates enhanced resistance to bacterial infections

The genetic predisposition to many autoimmune diseases is inherited as a polygenic trait. It is conceivable that some of the causative alleles in these diseases became prevalent in the population by conferring a survival benefit against environmental assaults, such as infections. We used mice cogenic for genetic loci predisposing to systemic lupus erythomatosus to test the hypothesis that some of these genetic loci protect the host from bacterial infections. Mice with the Sle3 lupus-susceptibility locus on a wild-type background were found to have enhanced antibacterial responses in the context of pneumonia and intra-abdominal sepsis than wild-type animals. This was associated with markedly augmented accumulation of neutrophils in infected tissues, and was bone marrow transferable and dependent on the presence of neutrophils, but not lymphocytes. There was no difference in in vitro leukocyte killing of bacteria nor influx of phagocytes between lupus-susceptible and wild-type animals, but neutrophils from lupus-susceptible mice displayed markedly reduced rate of apoptosis, associated with altered expression of Bcl-2 family proteins, contributing to their greater accumulation. Importantly, deliberate inhibition of apoptosis in wild-type animals significantly boosted the accumulation of neutrophils at the site of infection and resulted in an enhanced antimicrobial response. These observations support the concept that some of the genetic loci that mediate autoimmunity may also confer augmented antimicrobial innate immunity.

Genetic Dissection of Vasculitis, Myeloperoxidase-Specific Antineutrophil Cytoplasmic Autoantibody Production, and Related Traits in Spontaneous Crescentic Glomerulonephritis-Forming/Kinjoh Mice

The spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mouse is a model of human crescentic glomerulonephritis and vasculitis associated with the production of the myeloperoxidase (MPO)-specific antineutrophil cytoplasmic autoantibody (MPO-ANCA). Although the disease is mediated initially by mutation of the Fas gene (lpr), SCG/Kj mice also have non-Fas predisposing genetic factors. To define these factors, genome-wide quantitative trait locus (QTL) mapping was performed on female (B(6)x SCG/Kj) F(2) intercross mice. Fourteen non-Fas QTLs were identified. QTLs of glomerulonephritis were located on chromosomes 1, 10, 13, 16, and 17, vasculitis on chromosomes 1 and 17, splenomegaly on chromosome 1, hypergammaglobulinemia on chromosomes 1, 2, 4, 6, 7, 11, 13, and 17, antinuclear Ab on chromosomes 1, 8, 10, and 12, and MPO-ANCA production on chromosomes 1 and 10. Significant QTLs derived from SCG/Kj on chromosomes 1, 2, 7, and 13 were designated Scg-1 to Scg-5, respectively, and those derived from B(6) on chromosomes 4, 6, 17, and 10 were designated Sxb-1 to Sxb-4, respectively. Two loci linked to MPO-ANCA production on chromosomes 1 and 10 were designated Man-1 and Man-2 (for MPO-ANCA), respectively. Although both Scg-1 and Scg-2 were on chromosome 1 and shared several functions, it was of interest that aberrant MPO-ANCA production was exclusively controlled by Man-1, the centromeric half region of the Scg-2 chromosomal segment. We also examined the epistatic effects between the lpr mutation and non-Fas susceptibility genes. QTLs are discussed in relation to previously described loci, with emphasis on their candidate genes.

Genetic segregation of spontaneous erosive arthritis and generalized autoimmune disease in the BXD2 recombinant inbred strain of mice

The BXD2 strain of mice is one of approximately 80 BXD recombinant inbred (RI) mouse strains derived from an intercross between C57BL/6J (B6) and DBA/2J (D2) strains. We have discovered that adult BXD2 mice spontaneously develop generalized autoimmune disease, including glomerulonephritis (GN), increased serum titres of rheumatoid factor (RF) and anti-DNA antibody, and a spontaneous erosive arthritis characterized by mononuclear cell infiltration, synovial hyperplasia, and bone and cartilage erosion. The features of lupus and arthritis developed by the BXD2 mice segregate in F2 mice generated by crossing BXD2 mice with the parental B6 and D2 strains. Genetic linkage analysis of the serum levels of anti-DNA and RF by using the BXD RI strains shows that the serum titers of anti-DNA and RF were influenced by a genetic locus on mouse chromosome (Chr) 2 near the marker D2Mit412 (78 cm, 163 Mb) and on Chr 4 near D4Mit146 (53.6 cm, 109 Mb), respectively. Both loci are close to the B-cell hyperactivity, lupus or GN susceptibility loci that have been identified previously. The results of our study suggest that the BXD2 strain of mice is a novel model for complex autoimmune disease that will be useful in identifying the mechanisms critical for the immunopathogenesis and genetic segregation of lupus and erosive arthritis.

Genetic interactions between susceptibility loci reveal epistatic pathogenic networks in murine lupus

Interactions between Sle1 and other susceptibility loci were required for disease development in the NZM2410 model of lupus. Sle1 corresponds to at least three subloci, Sle1a, Sle1b, and Sle1c, each of which independently causes loss of tolerance to chromatin, but displays a distinctive immune profile. We have used congenic strains to analyze the interactions between the Sle1 subloci and other lupus susceptibility loci using Y autoimmunity accelerator (Yaa) and Faslpr as sensitizing mutations. Sle1 coexpressed with either one of these single susceptibility alleles resulted in a highly penetrant nephritis, splenomegaly, production of nephrophilic antibodies, and increased expression of B- and T-cell activation markers. Here, we show that only Sle1b interacted with Yaa to produce these phenotypes, suggesting that Sle1b and Yaa belong to the same functional pathway. Interactions between the three Sle1 loci and lpr resulted in lymphocyte activation and lupus nephritis, but a significant mortality was observed only for the Sle1a.lpr combination. This suggests a major role for the FAS pathway in keeping in check the loss of tolerance mediated by the Sle1 loci, especially for Sle1a. Our results illustrate the complexity of interactions between susceptibility loci in polygenic diseases such as lupus and may explain the clinical heterogeneity of the disease.

Illuminating autoimmune regulators through controlled variation of the mouse genome sequence

Gene variants in mice that have strong, Mendelian effects on autoimmune susceptibility have been one of the most productive entry points for identifying genes and processes regulating human autoimmunity. With the tools now available to map and identify new mouse Mendelian gene variants, the handful of spontaneous mutations accumulated over several decades have all been identified, and the main bottleneck lies in producing new Mendelian immune variants. We outline here a strategy to generate large sets of functional variants in genes controlling lupus and humoral immunity, based upon limited variation of the mouse genome sequence with the chemical mutagen, ENU, combined with a set of sensitive immunological screens.

A genetic lesion that arrests plasma cell homing to the bone marrow

The coordinated regulation of chemokine responsiveness plays a critical role in the development of humoral immunity. After antigen challenge and B cell activation, the emerging plasma cells (PCs) undergo CXCL12-induced chemotaxis to the bone marrow, where they produce Ab and persist. Here we show that PCs, but not B cells or T cells from lupus-prone NZM mice, are deficient in CXCL12-induced migration. PC unresponsiveness to CXCL12 results in a marked accumulation of PCs in the spleen of mice, and a concordant decrease in bone marrow PCs. Unlike normal mice, in NZM mice, a majority of the splenic PCs are long-lived. This deficiency is a consequence of the genetic interactions of multiple systemic lupus erythematosus susceptibility loci.

Lowering anti-dsDNA antibodies--what's new?

Antibodies to dsDNA are specific to SLE and are pathogenic, both due to their ability to deposit in tissues through a variety of mechanisms, and to their ability, when present in immune complexes, to activate inflammatory cells. The relationship of serum anti-dsDNA antibody levels to disease activity is a complex one and the factors that determine whether or not such antibodies will be pathogenic in an individual SLE patient are incompletely understood. Although anti-dsDNA antibodies can be made by naïve B cells and B cells belonging to the B1 and marginal zone subsets, pathogenic anti-dsDNA antibodies have the hallmarks of germinal center development and exposure to T cell help, including accumulation of somatic mutations and class switching to the IgG isotype. Epitope spreading may result in aquisition of cross-reactivities with multiple target organ antigens and aquisition of a memory phenotype will allow these B cells to acquire antigen presentation functions that amplify the autoreactive response. In the early stages of disease, or after remission induction protocols, autoreactive B cells may be susceptible to treatments that target T cell costimulation or that deplete or tolerize naïve and mature B cells. Therapeutic approaches targeting innate immune responses or regulatory T cells are starting to be tested in pre-clinical models. In later disease stages, memory and plasma cell accumulation may render patients more resistant to this type of therapeutic approach. Deposition of anti-dsDNA antibodies in target tissues can stimulate an inflammatory cascade that leads to tissue damage. A number of murine models have now been developed that show that interruption of this cascade can prevent or reverse such damage. This type of approach may be beneficial for individuals with established disease. As we learn more about the specific defects that cause SLE, it may become possible to individualize therapy based on patient specific biologic markers.

Positional identification of Ncf1 as a gene that regulates arthritis severity in rats

The identification of genes underlying quantitative-trait loci (QTL) for complex diseases, such as rheumatoid arthritis, is a challenging and difficult task for the human genome project. Through positional cloning of the Pia4 QTL in rats, we found that a naturally occurring polymorphism of Ncf1 (encoding neutrophil cytosolic factor 1, a component of the NADPH oxidase complex) regulates arthritis severity. The disease-related allele of Ncf1 has reduced oxidative burst response and promotes activation of arthritogenic T cells. Pharmacological treatment with substances that activate the NADPH oxidase complex is shown to ameliorate arthritis. Hence, Ncf1 is associated with a new autoimmune mechanism leading to severe destructive arthritis, notably similar to rheumatoid arthritis in humans.

The major murine systemic lupus erythematosus susceptibility locus Sle1 results in abnormal functions of both B and T cells

Sle1 is a major susceptibility locus in the NZM2410 murine model of systemic lupus erythematosus. When isolated on a C57BL/6 background in the B6.Sle1 congenic strain, Sle1 results in the production of high levels of anti-chromatin IgG Abs, histone-specific T cells, and increased B and T cell activation. We have shown by mixed bone marrow chimeras with allotypic markers that Sle1 is expressed in B cells. Using the same technique, we now show that it is also expressed in T cells. To assess whether Sle1 results in intrinsic defects in B or T cells, we have bred the muMT and Tcralpha(-/-) mutations onto B6.Sle1 resulting in the absence of circulating B cells and alphabeta T cells in B6.Sle1.muMT and B6.Sle1.Tcralpha(-/-), respectively. The immune phenotypes in these two strains were compared with that of B6.Sle1 and B6.muMT or B6.Tcralpha(-/-). Sle1-expressing B cells broke tolerance to chromatin in the absence of T cells, as shown by high levels of anti-ssDNA IgM Abs in B6.Sle1.Tcralpha(-/-) mice, and had an increased expression of activation markers. Conversely, increased expression of activation markers and increased cytokine production were observed in Sle1-expressing T cells in the absence of B cells in B6.Sle1.muMT mice. However, the production of IgG antinuclear Abs required the presence of both T and B cells. These experiments showed that Sle1 expression results in both B and T cells intrinsic defects and demonstrate that the documented involvement of each cell compartment in the production of anti-chromatin Abs corresponds to genetic defects rather than bystander effects.

Modulation of multiple experimental arthritis models by collagen-induced arthritis quantitative trait loci isolated in congenic rat lines: different effects of non-major histocompatibility complex quantitative trait loci in males and females

OBJECTIVE

Collagen-induced arthritis (CIA) is a model of inflammatory arthritis with many similarities to rheumatoid arthritis (RA). We previously mapped in F(2) offspring of CIA-susceptible DA and CIA-resistant F344 rats, 5 quantitative trait loci (QTLs) for which F344 alleles were associated with reduced CIA severity. In the present study, we sought to characterize the independent arthritis-modulating effects of these 5 QTLs.

METHODS

CIA-regulatory regions were transferred from the F344 genome to the DA background or vice versa by repeated backcrossing. The arthritis-modulating effects of the transferred alleles were determined by comparing the severity of experimentally induced arthritis in congenic rats with that in DA rats.

RESULTS

Congenic lines with either the F344 major histocompatibility complex (MHC) on the DA background or the DA MHC on the F344 background were resistant to CIA, confirming both MHC and non-MHC contributions to the genetic regulation of CIA. F344 alleles at the Cia3 and Cia5 regions of chromosomes 4 and 10 reduced CIA severity relative to that observed in DA rats. F344 Cia4 and Cia6 regions of chromosomes 7 and 8 failed to significantly alter CIA severity. Arthritis-modifying effects of Cia4 and Cia6 were, however, detected in pristane-induced and/or Freund's incomplete adjuvant oil-induced arthritis. The arthritis-modifying effects of the non-MHC CIA-regulatory loci differed in males and females.

CONCLUSION

These congenic lines confirmed the existence and location of genes that regulate the severity of experimental arthritis in rats. Mechanisms responsible for the sex-specificity of individual arthritis-regulatory loci may explain some of the sex differences observed in RA and other autoimmune diseases in humans.

Genome screening for susceptibility loci in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex, multigenic autoimmune disease with a wide spectrum of clinical manifestations. Much of the pathology is attributed to deposition to various tissues of immune complexes continuously formed with autoantibodies; thus, the pathogenesis is related to dysregulation of self-reactive B cells. Recent family linkage studies and allele-sharing linkage analyses of affected sibling pairs have advanced genome screening for susceptibility loci in SLE, and a considerable number of chromosomal intervals with significant or suggestive linkage to SLE have been identified. However, there are still several inherent difficulties in precisely identifying loci and genes, as the complexity of polygenic inheritance of SLE phenotypes is considerable. One must note that each specific aspect of diverse SLE phenotypes (clinical manifestations and immunological abnormalities) is mostly controlled separately by a different set of susceptibility loci. Involvement of positive and negative epistatic gene interactions often puzzles genetic analyses. Studies on SLE using murine lupus models are ongoing to solve some of these difficulties. Comparative studies have identified several syntenic chromosomal intervals with susceptibility loci in both mouse models and humans. Thus, combining knowledge derived from both human and murine studies is vital. The ultimate identification of susceptibility genes and their functions will probably depend largely on studies using genetically manipulated mutant mice, including those with homologous recombination of potent polymorphic target genes. The up-coming completion of genomic sequences in mice and humans is predicted to limit the numbers of potent candidate genes in particular genomic intervals and accelerates this line of studies. Such knowledge will lead to elucidation of genetic and cellular mechanisms involved in the dysregulation of self-reactive lymphocytes in the pathogenesis of SLE. Prophylactic and therapeutic clinical approaches can then be better designed.

Of mice and men: the relevance of the mouse to the study of human SLE

A number of mouse models have been utilized to study the pathophysiology of immune complex (IC) disease, and the hallmark IC disease systemic lupus erythematosus (SLE). Many of these studies have provided exciting new insights into IC-mediated inflammation and autoimmunity. However, numerous differences exist between mice and humans that suggest that mouse studies are not always applicable to human disease. These differences can be found in the biological systems that interact with circulating IC, in the specifics of disease presentation, and in the general physiology of the two species. Furthermore, although the mechanisms of SLE-like autoimmune disease in the mouse are being defined through analyses of the murine models of SLE, it remains to be proven that these mechanisms are relevant to human SLE. Thus, generalizing the results of the mouse studies to human SLE and other human IC diseases must be done with caution.

Susceptibility genes in the pathogenesis of murine lupus

Systemic lupus erythematosus (SLE) is the paradigm of a multisystem autoimmune disease in which genetic factors strongly influence susceptibility. Through genome scans and congenic dissection, numerous loci associated with lupus susceptibility have been defined and the complexity of the inheritance of this disease has been revealed. In this review, we provide a brief description of animal models of SLE, both spontaneous models and synthetic models, with an emphasis on the B6 congenic model derived from analyses of the NZM2410 strain. A hypothetical model of disease progression that organizes many of the identified SLE susceptibility loci in three distinct biological pathways that interact to mediate disease pathogenesis is also described. We finally discuss our recent fine mapping analysis, which revealed a cluster of loci that actually comprise the Sle1 locus.