Genetic Determination of T Cell Help in Loss of Tolerance to Nuclear Antigens

Regulation of the STAT3 pathway by lupus susceptibility gene Pbx1 in T cells

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease in which poorly characterized genetic factors lead to the production of proinflammatory or autoreactive T cells. Pre-B cell leukemia homeobox 1 (PBX1) is a transcription factor whose dominant negative isoform (PBX1-D) is overexpressed in the CD4+ T cells of SLE patients and lupus-prone mice. Pbx1-D overexpression favors the expansion of proinflammatory T cells and impairs regulatory T (Treg) cell development. Here we show that Pbx1 deficiency and Pbx1-D overexpression decreased STAT3 expression and activation in T cells. Accordingly, Pbx1 deficiency in T cells and Pbx1-D overexpression reduced STAT3-dependent TH17 cell polarization in vitro, but it had no effect in vivo at steady state. STAT3-dependent follicular helper T (TFH) cell polarization in vitro and splenic TFH cell frequency were not affected by either Pbx1 deficiency or Pbx1-D overexpression. Pbx1 deficiency also increased the expression of cell cycle arrest and pro-apoptotic genes, with an increased apoptosis in T cells. Our results suggest a complex interplay between PBX1 and STAT3, which may contribute to lupus pathogenesis through dysregulation of the cell cycle and apoptosis.

Molecular Mechanisms of Lupus Susceptibility Allele PBX1D

Pre-B cell leukemia homeobox 1 (PBX1) controls chromatin accessibility to a large number of genes in various cell types. Its dominant negative splice isoform, PBX1D, which lacks the DNA and Hox-binding domains, is expressed more frequently in the CD4+ T cells from lupus-prone mice and patients with systemic lupus erythematosus than healthy control subjects. PBX1D overexpression in CD4+ T cells impaired regulatory T cell homeostasis and expanded inflammatory CD4+ T cells. In this study, we showed that PBX1 message expression is downregulated by activation in CD4+ T cells as well as in B cells. PBX1D protein was less stable than the normal isoform, PBX1B, and it is degraded through the ubiquitin-proteasome-dependent pathway. The DNA binding domain lacking in PBX1D has two putative ubiquitin binding sites, K292 and K293, that are predicted to be in direct contact with DNA. Mutation of K292-293 reduced PBX1B stability to a level similar to PBX1D and abrogated DNA binding. In addition, contrary to PBX1B, PBX1D is retained in the cytoplasm without the help of the cofactors MEIS or PREP1, indicating a different requirement for nuclear translocation. Overall, these findings suggest that multiple post-transcriptional mechanisms are responsible for PBX1D loss of function and induction of CD4+ T cell inflammatory phenotypes in systemic lupus erythematosus.

Dysregulation and chronicity of pathogenic T cell responses in the pre-diseased stage of lupus

In the normal immune system, T cell activation is tightly regulated and controlled at several levels to ensure that activation occurs in the right context to prevent the development of pathologic conditions such as autoimmunity or other harmful immune responses. CD4+FoxP3+ regulatory T cells (Treg) are crucial for the regulation of T cell responses in the peripheral lymphatic organs and thus for the prevention and control of autoimmunity. In systemic lupus erythematosus (SLE), a prototypic systemic autoimmune disease with complex etiology, a disbalance between Treg and pathogenic effector/memory CD4+ T cells develops during disease progression indicating that gradual loss of control over T cell activation is an important event in the immune pathogenesis. This progressive failure to adequately regulate the activation of autoreactive T cells facilitates chronic activation and effector/memory differentiation of pathogenic T cells, which are considered to contribute significantly to the induction and perpetuation of autoimmune processes and tissue inflammation in SLE. However, in particular in humans, little is known about the factors which drive the escape from immune regulation and the chronicity of pathogenic T cell responses in an early stage of autoimmune disease when clinical symptoms are still unapparent. Here we briefly summarize important findings and discuss current views and models on the mechanisms related to the dysregulation of T cell responses which promotes chronicity and pathogenic memory differentiation with a focus on the early stage of disease in lupus-prone individuals.

Genetic Variations Controlling Regulatory T Cell Development and Activity in Mouse Models of Lupus-Like Autoimmunity

Immune homeostasis is a constant balancing act between effector T cells and regulatory T cells defined by Foxp3 expression, the transcription factor that drives their differentiation and immunosuppressive activity. Immune homeostasis is altered when Treg cells are not generated or maintained in sufficient numbers. Treg cells rendered unstable by loss of Foxp3 expression, known as ex-Treg cells, gain pro-inflammatory functions. Treg cells may also become dysfunctional and lose their suppressive capabilities. These alterations can cause an imbalance between effector and regulatory subsets, which may ultimately lead to autoimmunity. This review discusses recent studies that identified genetic factors that maintain Treg cell stability as well as preserve their suppressive function. We focus on studies associated with systemic lupus erythematosus and highlight their findings in the context of potential therapeutic gene targeting in Treg cells to reverse the phenotypic changes and functional dysregulation inducing autoimmunity.

Estrogen Receptor Alpha Signaling Is Responsible for the Female Sex Bias in the Loss of Tolerance and Immune Cell Activation Induced by the Lupus Susceptibility Locus Sle1b

The dramatic female sex bias observed in human lupus is thought to be due, at least in part, to estrogens. Using mouse models, we have shown that estrogens, acting through estrogen receptor alpha (ERα) promote lupus development and contribute significantly to the female sex bias observed in this disease. C57Bl/6 (B6) mice carrying the lupus susceptibility locus Sle1 locus exhibit immune cell hyperactivation and loss of tolerance, and the action of Sle1 displays a strong female sex bias. Previously, we showed that disruption of ERα completely eliminates the female sex bias in the effects of Sle1. Here we report that ERα signaling selectively modulates the action of Sle1b, one of the three subloci that together constitute Sle1. We observed that disruption of ERα signaling attenuated T cell hyperactivation, formation of spontaneous germinal centers, loss of tolerance, and the development of anti-chromatin autoantibodies in B6.Sle1b female mice, but had no impact on these phenotypes in B6.Sle1b male mice. In fact, disruption of ERα completely abolished the female sex bias that is seen in each of these phenotypes in B6.Sle1b mice. Strikingly, Sle1b-induced B cell hyperactivation, a female sex-specific manifestation of Sle1b, was completely abrogated by disruption of ERα in B6.Sle1b females. Altogether, these results demonstrate that ERα signaling is responsible for the female sex bias in the actions of Sle1b, and is absolutely required for the female-specific B cell hyperactivation phenotype associated with this lupus susceptibility locus. By contrast, we found that ERα signaling had no impact on Sle1a, the other Sle1 sublocus that exerts effects that show a female sex bias.

Histone H2A-Reactive B Cells Are Functionally Anergic in Healthy Mice With Potential to Provide Humoral Protection Against HIV-1

Peripheral tolerance is essential for silencing weakly autoreactive B cells that have escaped central tolerance, but it is unclear why these potentially pathogenic B cells are retained rather than being eliminated entirely. Release from peripheral tolerance restraint can occur under certain circumstances (i.e., strong TLR stimulus), that are present during infection. In this regard, we hypothesized that autoreactive B cells could function as a reserve population that can be activated to contribute to the humoral immune response, particularly with pathogens, such as HIV-1, that exploit immune tolerance to avoid host defense. In this study, we identify a population of autoreactive B cells with the potential to neutralize HIV-1 and experimentally release them from the functional restrictions of peripheral tolerance. We have previously identified murine monoclonal antibodies that displayed autoreactivity against histone H2A and neutralized HIV-1 in vitro. Here, we identify additional H2A-reactive IgM monoclonal antibodies and demonstrate that they are both autoreactive and polyreactive with self and foreign antigens and are able to neutralize multiple clades of tier 2 HIV-1. Flow cytometric analysis of H2A-reactive B cells in naïve wildtype mice revealed that these B cells are present in peripheral B cell populations and we further document that murine H2A-reactive B cells are restrained by peripheral tolerance mechanisms. Specifically, we show endogenous H2A-reactive B cells display increased expression of the inhibitory mediators CD5 and phosphatase and tensin homolog (PTEN) phosphatase and fail to mobilize calcium upon immunoreceptor stimulation; all characterized markers of anergy. Moreover, we show that toll-like receptor stimulation or provision of CD4 T cell help induces the in vitro production of H2A-reactive antibodies, breaking tolerance. Thus, we have identified a novel poly/autoreactive B cell population that has the potential to neutralize HIV-1 but is silenced by immune tolerance.

T cells expressing the lupus susceptibility allele Pbx1d enhance autoimmunity and atherosclerosis in dyslipidemic mice

Patients with systemic lupus erythematosus (SLE) present a high incidence of atherosclerosis, which contributes significantly to morbidity and mortality in this autoimmune disease. An impaired balance between regulatory (Treg) and follicular helper (Tfh) CD4+ T cells is shared by both diseases. However, whether there are common mechanisms of CD4+ T cell dysregulation between SLE and atherosclerosis remains unclear. Pre-B cell leukemia transcription factor 1 isoform d (Pbx1d) is a lupus susceptibility gene that regulates Tfh cell expansion and Treg cell homeostasis. Here, we investigated the role of T cells overexpressing Pbx1d in low-density lipoprotein receptor-deficient (Ldlr-/-) mice fed with a high-fat diet, an experimental model for atherosclerosis. Pbx1d-transgenic T cells exacerbated some phenotypes of atherosclerosis, which were associated with higher autoantibody production, increased Tfh cell frequency, and impaired Treg cell regulation, in Ldlr-/- mice as compared with control T cells. In addition, we showed that dyslipidemia and Pbx1d-transgenic expression independently impaired the differentiation and function of Treg cells in vitro, suggesting a gene/environment additive effect. Thus, our results suggest that the combination of Pbx1d expression in T cells and dyslipidemia exacerbates both atherosclerosis and autoimmunity, at least in part through a dysregulation of Treg cell homeostasis.

Pregnancy in Women With Systemic Lupus and Lupus Nephritis

Pregnancy is an altered immunologic state in which hormonal changes impact the immune system to enable maternal tolerance of the fetus. These hormonal and immunologic changes may affect disease activity in systemic lupus erythematosus. Conversely, lupus nephritis and its complications may adversely impact pregnancy. Systemic lupus erythematosus increases the risk of pre-eclampsia and its complications, including preterm birth and intrauterine growth restriction. Comorbidities such as impaired kidney function and hypertension confer additional risk and complexity. Medications used to treat lupus nephritis may impact the fetus, so therapy needs to be tailored to balance maternal benefit and fetal risk. The diagnosis of lupus nephritis during pregnancy can be difficult, as it shares overlapping features with pre-eclampsia. Kidney biopsy is generally safe in pregnancy, and should be considered if the result will affect management. Here we review the clinical aspects of counseling, diagnosis, and management of lupus nephritis in pregnancy.

Sex Hormones in Acquired Immunity and Autoimmune Disease

Women have stronger immune responses to infections and vaccination than men. Paradoxically, the stronger immune response comes at a steep price, which is the high incidence of autoimmune diseases in women. The reasons why women have stronger immunity and higher incidence of autoimmunity are not clear. Besides gender, sex hormones contribute to the development and activity of the immune system, accounting for differences in gender-related immune responses. Both innate and adaptive immune systems bear receptors for sex hormones and respond to hormonal cues. This review focuses on the role of sex hormones particularly estrogen, in the adaptive immune response, in health, and autoimmune disease with an emphasis on systemic lupus erythematosus.

Relative Contributions of B Cells and Dendritic Cells from Lupus-Prone Mice to CD4+ T Cell Polarization

Mouse models of lupus have shown that multiple immune cell types contribute to autoimmune disease. This study sought to investigate the involvement of B cells and dendritic cells in supporting the expansion of inflammatory and regulatory CD4⁺ T cells that are critical for lupus pathogenesis. We used lupus-prone B6.NZM2410.Sle1.Sle2.Sle3 (TC) and congenic C57BL/6J (B6) control mice to investigate how the genetic predisposition of these two cell types controls the activity of normal B6 T cells. Using an allogeneic in vitro assay, we showed that TC B1-a and conventional B cells expanded Th17 cells significantly more than their B6 counterparts. This expansion was dependent on CD86 and IL-6 expression and mapped to the Sle1 lupus-susceptibility locus. In vivo, TC B cells promoted greater differentiation of CD4⁺ T cells into Th1 and follicular helper T cells than did B6 B cells, but they limited the expansion of Foxp3 regulatory CD4⁺ T cells to a greater extent than did B6 B cells. Finally, when normal B6 CD4⁺ T cells were introduced into Rag1^-/- mice, TC myeloid/stromal cells caused their heightened activation, decreased Foxp3 regulatory CD4⁺ T cell differentiation, and increased renal infiltration of Th1 and Th17 cells in comparison with B6 myeloid/stromal cells. The results show that B cells from lupus mice amplify inflammatory CD4⁺ T cells in a nonredundant manner with myeloid/stromal cells.

Effects of oral Lactobacillus administration on antioxidant activities and CD4+CD25+forkhead box P3 (FoxP3)+ T cells in NZB/W F1 mice

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterised by a dysregulation of the immune system, which causes inflammation responses, excessive oxidative stress and a reduction in the number of cluster of differentiation (CD)4+CD25+forkhead box P3 (FoxP3)+ T cells. Supplementation with certain Lactobacillus strains has been suggested to be beneficial in the comprehensive treatment of SLE. However, little is known about the effect and mechanism of certain Lactobacillus strains on SLE. To investigate the effects of Lactobacillus on SLE, NZB/W F1 mice were orally gavaged with Lactobacillus paracasei GMNL-32 (GMNL-32), Lactobacillus reuteri GMNL-89 (GMNL-89) and L. reuteri GMNL-263 (GMNL-263). Supplementation with GMNL-32, GMNL-89 and GMNL-263 significantly increased antioxidant activity, reduced IL-6 and TNF-α levels and significantly decreased the toll-like receptors/myeloid differentiation primary response gene 88 signalling in NZB/W F1 mice. Notably, supplementation with GMNL-263, but not GMNL-32 and GMNL-89, in NZB/W F1 mice significantly increased the differentiation of CD4+CD25+FoxP3+ T cells. These findings reveal beneficial effects of GMNL-32, GMNL-89 and GMNL-263 on NZB/W F1 mice and suggest that these specific Lactobacillus strains can be used as part of a comprehensive treatment of SLE patients.

Multiple tolerance defects contribute to the breach of B cell tolerance in New Zealand Black chromosome 1 congenic mice

Lupus is characterized by a loss of B cell tolerance leading to autoantibody production. In this study, we explored the mechanisms underlying this loss of tolerance using B6 congenic mice with an interval from New Zealand Black chromosome 1 (denoted c1(96–100)) sufficient for anti-nuclear antibody production. Transgenes for soluble hen egg white lysozyme (sHEL) and anti-HEL immunoglobulin were crossed onto this background and various tolerance mechanisms examined. We found that c1(96–100) mice produced increased levels of IgM and IgG anti-HEL antibodies compared to B6 mice and had higher proportions of germinal center B cells and long-lived plasma cells, suggesting a germinal center-dependent breach of B cell anergy. Consistent with impaired anergy induction, c1(96–100) double transgenic B cells showed enhanced survival and CD86 upregulation. Hematopoietic chimeric sHEL mice with a mixture of B6 and c1(96–100) HEL transgenic B cells recapitulated these results, suggesting the presence of a B cell autonomous defect. Surprisingly, however, there was equivalent recruitment of B6 and c1(96–100) B cells into germinal centers and differentiation to splenic plasmablasts in these mice. In contrast, there were increased proportions of c1(96–100) T follicular helper cells and long-lived plasma cells as compared to their B6 counterparts, suggesting that both B and T cell defects are required to breach germinal center tolerance in this model. This possibility was further supported by experiments showing an enhanced breach of anergy in double transgenic mice with a longer chromosome 1 interval with additional T cell defects.

New insights into the immunopathogenesis of systemic lupus erythematosus

The aetiology of systemic lupus erythematosus (SLE) is multifactorial, and includes contributions from the environment, stochastic factors, and genetic susceptibility. Great gains have been made in understanding SLE through the use of genetic variant identification, mouse models, gene expression studies, and epigenetic analyses. Collectively, these studies support the concept that defective clearance of immune complexes and biological waste (such as apoptotic cells), neutrophil extracellular traps, nucleic acid sensing, lymphocyte signalling, and interferon production pathways are all central to loss of tolerance and tissue damage. Increased understanding of the pathogenesis of SLE is driving a renewed interest in targeted therapy, and researchers are now on the verge of developing targeted immunotherapy directed at treating either specific organ system involvement or specific subsets of patients with SLE. Accordingly, this Review places these insights within the context of our current understanding of the pathogenesis of SLE and highlights pathways that are ripe for therapeutic targeting.

The PBX1 lupus susceptibility gene regulates CD44 expression

PBX1-d is novel splice isoform of pre-B-cell leukemia homeobox 1 (PBX1) that lacks its DNA-binding and Hox-binding domains, and functions as a dominant negative. We have shown that PBX1-d expression in CD4+ T cells is associated with systemic lupus erythematosus (SLE) in a mouse model as well as in human subjects. More specifically, PBX1-d expression leads to the production of autoreactive activated CD4+ T cells, a reduced frequency and function of Foxp3+ regulatory T (Treg) cells and an expansion of follicular helper T (Tfh) cells. Very little is known about the function of PBX1 in T cells, except that it directly regulates the expression of miRNAs associated with Treg and Tfh homeostasis. In the present study, we show that PBX1 directly regulated the expression of CD44, a marker of T cell activation. Two PBX1 binding sites in the promoter directly regulated CD44 expression, with PBX1-d driving a higher expression than the normal isoform PBX1-b. In addition, mutations in each of the two binding sites had different effects of PBX1-b and PBX1-d. Finally, we showed that an enhanced recruitment of co-factor MEIS by PBX1-d over PBX1-b, while there was no difference for co-factor PREP1 recruitment. Therefore, this study demonstrates that the lupus-associated PBX1-d isoform directly transactivates CD44, a marker of CD44 activation and memory, and that it has different DNA binding and co-factor recruitment relative to the normal isoform. Taken together, these results confirm that PBX1 directly regulates genes related to T cell activation and shows that the lupus-associated isoform PBX1-d has unique molecular functions.

The Lupus Susceptibility Gene Pbx1 Regulates the Balance between Follicular Helper T Cell and Regulatory T Cell Differentiation

Pbx1 controls chromatin accessibility to a large number of genes and is entirely conserved between mice and humans. The Pbx1-d dominant-negative isoform is more frequent in CD4(+) T cells from lupus patients than from healthy controls. Pbx1-d is associated with the production of autoreactive T cells in mice carrying the Sle1a1 lupus-susceptibility locus. Transgenic (Tg) expression of Pbx1-d in CD4(+) T cells reproduced the phenotypes of Sle1a1 mice, with increased inflammatory functions of CD4(+) T cells and impaired Foxp3(+) regulatory T cell (Treg) homeostasis. Pbx1-d-Tg expression also expanded the number of follicular helper T cells (TFHs) in a cell-intrinsic and Ag-specific manner, which was enhanced in recall responses and resulted in Th1-biased Abs. Moreover, Pbx1-d-Tg CD4(+) T cells upregulated the expression of miR-10a, miR-21, and miR-155, which were implicated in Treg and follicular helper T cell homeostasis. Our results suggest that Pbx1-d impacts lupus development by regulating effector T cell differentiation and promoting TFHs at the expense of Tregs. In addition, our results identify Pbx1 as a novel regulator of CD4(+) T cell effector function.

Loss of Immune Tolerance Is Controlled by ICOS in Sle1 Mice

ICOS, a member of the CD28 family, represents a key molecule that regulates adaptive responses to foreign Ags. ICOS is prominently expressed on T follicular helper (TFH) cells, a specialized CD4(+) T cell subset that orchestrates B cell differentiation within the germinal centers and humoral response. However, the contribution of ICOS and TFH cells to autoantibody profiles under pathological conditions has not been thoroughly investigated. We used the Sle1 lupus-prone mouse model to examine the role of ICOS in the expansion and function of pathogenic TFH cells. Genetic deletion of ICOS impacted the expansion of TFH cells in B6.Sle1 mice and inhibited the differentiation of B lymphocytes into plasma cells. The phenotypic changes observed in B6.Sle1-ICOS-knockout mice were also associated with a significant reduction in class-switched IgG, and anti-nucleosomal IgG-secreting B cells compared with B6.Sle1 animals. The level of vascular cell adhesion protein 1, a molecule that was shown to be elevated in patients with SLE and in lupus models, was also increased in an ICOS-dependent manner in Sle1 mice and correlated with autoantibody levels. The elimination of ICOS-expressing CD4(+) T cells in B6.Sle1 mice, using a glyco-engineered anti-ICOS-depleting Ab, resulted in a significant reduction in anti-nucleosomal autoantibodies. Our results indicate that ICOS regulates the ontogeny and homeostasis of B6.Sle1 TFH cells and influences the function of TFH cells during aberrant germinal center B cell responses. Therapies targeting the ICOS signaling pathway may offer new opportunities for the treatment of lupus and other autoimmune diseases.

The murine Pbx1-d lupus susceptibility allele accelerates mesenchymal stem cell differentiation and impairs their immunosuppressive function

Pre–B cell leukemia homeobox 1 (Pbx1)-d is a dominant-negative splice isoform of the gene Pbx1 that corresponds to the NZM2410 lupus susceptibility locus Sle1a1. Pbx1 is required to maintain stem cell self-renewal, including that of mesenchymal stem cells (MSCs). MSCs have immunosuppressive functions that require stem cell maintenance. We tested the hypothesis that the expression of Pbx1-d favors MSC differentiation and impairs their immunosuppressive functions. We demonstrate that Sle1a1 MSCs express high levels of Pbx1-d as compared with congenic C57BL/6J (B6) MSCs. Sle1a1 MSCs grew faster and differentiated significantly more rapidly into osteoblasts than did B6 MSCs. This corresponded to a significant decrease in the expression of genes associated with stemness and an increase in the expression of genes associated with differentiation. Additionally, Sle1a1 MSCs express a gene expression profile associated with an enhanced innate immunity and inflammation. Suppression of Ig production from TLR-activated B6 B cells and IL-2 secretion from activated B6 CD4+ T cells was significantly impaired in Sle1a1 MSCs as compared with B6 MSCs. B6.Sle1a1 MSCs showed intermediate activity in suppressing lupus immunophenotypes in three different mouse models. Taken together, these data suggest that the expression of the lupus susceptibility allele Pbx1-d isoform impairs MSC functions, which may contribute to lupus pathogenesis both through a defective immunosuppression and the promotion of a proinflammatory environment.

Genetic and cellular dissection of the activation of AM14 rheumatoid factor B cells in a mouse model of lupus

The RF-specific AM14 tg BCR has been used as a model to dissect the mechanisms of B cell tolerance to ICs containing nucleic acids. We have shown previously that AM14 RF B cells break tolerance in the TC mouse model of lupus through the dual engagement of the AM14 BCR and TLR9. In this study, we showed that neither the expression of Sle1 or Sle2 susceptibility loci alone was sufficient to activate AM14 RF B cells, suggesting that the production of antichromatin IgG2a(a) autoAg mediated by Sle1 and an intrinsically higher B cell activation mediated by Sle2 were required. We also showed that the B6 genetic background enhanced the selection of AM14 RF B cells to the MZB cell compartment regardless of the expression of the Sle loci and therefore, of their activation into AFCs. Furthermore, some AM14 RF B cells were selected into the B-1a compartment, where they did not differentiate into AFCs. Therefore, it is unlikely that the selection of AM14 RF B cells to the MZB or B-1a cell compartments in TC.AM14(a) mice is responsible for their breach of tolerance. Finally, we showed that the presence of expression of Sle1 in non-tg cells, most likely T cells, is necessary for the activation of AM14 RF B cells into AFCs. Overall, these results suggest a threshold model of activation of AM14 RF B cells on the B6 background with additive genetic and cellular contribution of multiple sources.

Estrogen receptor alpha signaling promotes Sle1-induced loss of tolerance and immune cell activation and is responsible for sex bias in B6.Sle1 congenic mice

Sex bias in lupus incidence is thought to be due, in part, to the ability of estrogens to promote loss of tolerance. Previously, we showed that estrogens promote lupus via estrogen receptor α (ERα). C57BL/6 (B6) mice carrying the Sle1 lupus susceptibility locus (B6.Sle1) display loss of tolerance and develop anti-nuclear antibodies and immune cell hyperactivation. The incidence of loss of tolerance in B6.Sle1 females is greater than in males. Here, we show that a deficiency of either estrogens or ERα attenuates loss of tolerance and autoantibody development in B6.Sle1 females. Furthermore, we demonstrate that immune cell activation in B6.Sle1 mice shows sex bias and that ERα deficiency diminishes this phenotype in B6.Sle1 females. Thus, estrogens, acting via ERα, control sex bias in the Sle1 phenotype. Furthermore, we show that ERα may impact the Sle1 phenotype by modulating the expression of Pbx1, one of genes that underlies the Sle1 locus.

The development of autoimmune features in aging mice is closely associated with alterations of the peripheral CD4⁺ T-cell compartment

Some signs of potential autoimmunity, such as the appearance of antinuclear antibodies (ANAs) become prevalent with age. In most cases, elderly people with ANAs remain healthy. Here, we investigated whether the same holds true for inbred strains of mice. Indeed, we show that most mice of the C57BL/6 (B6) strain spontaneously produced IgG ANA at 8-12 months of age, showed IgM deposition in kidneys and lymphocyte infiltrates in submandibular salivary glands. Despite all of this, the mice remained healthy. ANA production is likely CD4(+) T-cell dependent, since old (40-50 weeks of age) B6 mice deficient for MHC class II do not produce IgG ANAs. BM chimeras showed that ANA production was not determined by age-related changes in radiosensitive, hematopoietic progenitor cells, and that the CD4(+) T cells that promote ANA production were radioresistant. Thymectomy of B6 mice at 5 weeks of age led to premature alterations in T-cell homeostasis and ANA production, by 15 weeks of age, similar to that in old mice. Our findings suggest that a disturbed T-cell homeostasis may drive the onset of some autoimmune features.

Susceptibility quantitative trait loci for pathogenic leucocytosis in SCG/Kj mice, a spontaneously occurring crescentic glomerulonephritis and vasculitis model

The spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mouse, a model of human crescentic glomerulonephritis (CrGN) and systemic vasculitis, is characterized by the production of myeloperoxidase-specific anti-neutrophil cytoplasmic autoantibody (MPO-ANCA) and marked leucocytosis. This study was performed to identify the specific populations of leucocytes associated with CrGN and susceptibility loci for pathogenic leucocytosis. Four hundred and twenty female (C57BL/6 × SCG/Kj) F2 intercross mice were subjected to serial flow cytometry examination of the peripheral blood (PB). Kidney granulocytes and monocytes were examined histopathologically. Linkage analyses were performed with 109 polymorphic microsatellite markers. Correlation studies revealed that increase of the granulocytes, F4/80(+) cells, CD3(+) CD4(-) CD8(-) T cells and dendritic cells (DCs) in peripheral blood (PB) were associated significantly with glomerulonephritis, crescent formation and vasculitis. In kidney sections, F4/80(low) cells were observed in crescent, while F4/80(high) cells were around the Bowman's capsules and in the interstitium. Numbers of F4/80(+) cells in crescents correlated significantly with F4/80(+) cell numbers in PB, but not with numbers of F4/80(+) cells in the interstitium. Genome-wide quantitative trait locus (QTL) mapping revealed three SCG/Kj-derived non-Fas QTLs for leucocytosis, two on chromosome 1 and one on chromosome 17. QTLs on chromosome 1 affected DCs, granulocytes and F4/80(+) cells, but QTL on chromosome 17 affected DCs and granulocytes. We found CrGN-associated leucocytes and susceptibility QTLs with their positional candidate genes. F4/80(+) cells in crescents are considered as recruited inflammatory macrophages. The results provide information for leucocytes to be targeted and genetic elements in CrGN and vasculitis.

Relationship between gut microbiota and development of T cell associated disease

The interplay between the immune response and the gut microbiota is complex. Although it is well-established that the gut microbiota is essential for the proper development of the immune system, recent evidence indicates that the cells of the immune system also influence the composition of the gut microbiota. This interaction can have important consequences for the development of inflammatory diseases, including autoimmune diseases and allergy, and the specific mechanisms by which the gut commensals drive the development of different types of immune responses are beginning to be understood. Furthermore, sex hormones are now thought to play a novel role in this complex relationship, and collaborate with both the gut microbiota and immune system to influence the development of autoimmune disease. In this review, we will focus on recent studies that have transformed our understanding of the importance of the gut microbiota in inflammatory responses.

Effects of cystamine on antioxidant activities and regulatory T cells in lupus-prone mice

Attenuated antioxidant activities, irregular cytokines expressions and reduced regulatory T cells, are strongly associated with the pathogenesis of systemic lupus erythematosus (SLE). Despite the well-established beneficial effects of cystamine on lupus-prone mice, the extent to which cystamine contributes to antioxidant activity and the reduction of regulatory T cells has seldom been investigated. Therefore, this study elucidates how cystamine affects anti-oxidant activities in NZB/W F1 mice by performing assays of Glutathione (GSH), 1,1-diphenyl-2- picryl-hydrazyl (DPPH) and malondialdehyde thiobarbituric acid (MDA). In addition, investigations of the effects of cystamine on CD4⁺/CD25⁺ regulatory T cells and interleukin-6 (IL6)/STAT-3 signalling were performed with flow cytometry and immunoblots. Experimental results reveal more significantly reduced MDA and increased GSH and DPPH in NZB/W F1 mice receiving cystamine than in those mice receiving PBS. Meanwhile, CD4⁺/CD25⁺ regulatory T cells more significantly increase in NZB/W F1 mice receiving cystamine than in those mice receiving PBS, accompanied by significantly reduced IL-6/phosphorylated STAT-3 expression. The above findings suggest the beneficial effects of cystamine in terms of increasing antioxidant activities and CD4⁺/CD25⁺ regulatory T cells in lupus-prone mice by suppressing IL-6/STAT3 signalling.

The NZM2410-derived lupus susceptibility locus Sle2c1 increases Th17 polarization and induces nephritis in fas-deficient mice

OBJECTIVE

Sle2 is a lupus susceptibility locus that has been linked to glomerulonephritis in the NZM2410 mouse. By itself, Sle2 does not induce any autoimmune pathology but results in the accumulation of B-1a cells. This study was designed to assess the contribution of Sle2 to the pathogenesis of autoimmunity.

METHODS

Sle2 or its subcongenic intervals (Sle2a, Sle2b, and Sle2c1) were bred to Fas-deficient B6.lpr mice. Lymphoid phenotypes, which were focused on T cells, were assessed by flow cytometry, and histopathologic changes were compared between cohorts of B6.Sle2.lpr congenic mice and B6.lpr mice of ages up to 6 months.

RESULTS

Sle2 synergized with lpr, resulting in a greatly accelerated lymphadenopathy that largely targeted T cells and mapped to the Sle2c1 locus. This locus has been identified as the main contributor to B-1a cell expansion. Further analyses showed that Sle2c1 expression skewed the differentiation and polarization of Fas-deficient T cells, with a reduction of the CD4+CD25+FoxP3+ regulatory T cell subset and an expansion of the Th17 cells. This was associated with a high number of T cell infiltrates that promoted severe nephritis and dermatitis in the B6.Sle2c1.lpr mice.

CONCLUSION

These results show that Sle2c1 contributes to lupus pathogenesis by affecting T cell differentiation in combination with other susceptibility loci, such as lpr. The significance of the cosegregation of this phenotype and B-1a cell expansion in Sle2c1-expressing mice in relation to the pathogenesis of lupus is discussed.

T-regs in autoimmune hepatitis-systemic lupus erythematosus/mixed connective tissue disease overlap syndrome are functionally defective and display a Th1 cytokine profile

Autoimmune hepatitis (AIH), a severe hepatopathy characterized by hypergammaglobulinaemia, autoantibodies and interface hepatitis, is occasionally associated with systemic autoimmune manifestations [systemic lupus erythematosus (SLE); mixed connective tissue disease (MCTD)]. In both AIH and SLE/MCTD numerical and/or functional impairment of regulatory T-cells (T-regs) is believed to favour autoimmunity. To investigate whether immune-tolerance breakdown profiles differ in patients with AIH and SLE/MCTD, isolated AIH or systemic autoimmunity, we studied phenotypic and functional features of T-regs in 10 patients with AIH-SLE/MCTD, 22 with AIH, 12 with SLE and 20 healthy subjects. Compared to health, CD4(pos)CD25(pos) cells were decreased in number and expressed high levels of the CD127 activation marker in all three disease groups; in AIH-SLE/MCTD and in SLE they displayed low levels of FOXP3. In AIH-SLE/MCTD, they also contained a high proportion of IFNγ positive cells, indicating a Th1 profile. Similarly, in AIH-SLE/MCTD, CD4(pos)CD25(pos)CD25(high) T-regs were reduced in number and contained an increased proportion of activated CD127(pos) and IFNγ(pos) cells. Such skewing towards a Th1 profile was also present at effector level, as a high frequency of IFNγ-producing cells was observed within AIH-SLE/MCTD CD4(pos)CD25(neg) responder cells. Impairment in suppressor function both of CD4(pos)CD25(pos) cells and CD4(pos)CD25(pos)CD127(neg) T-regs was observed in all three autoimmune conditions, but while addition of CD4(pos)CD25(pos)CD127(neg) T-regs decreased CD4(pos)CD25(neg) responder cell proliferation in healthy subjects and partially in AIH patients, it had no effect in AIH-SLE/MCTD and SLE patients. In conclusion, in AIH-SLE/MCTD T-regs display a distinctive phenotypic and functional signature, characterized by marked activation, elevated IFNγ production and by a profound impairment of suppressive function, suggesting that multiple autoimmune manifestations may derive from a complex defect of immune-regulation.

The SLE-associated Pbx1-d isoform acts as a dominant-negative transcriptional regulator

Pbx1 is a transcription factor involved in multiple cellular processes, including the maintenance of self-renewal of hematopoietic progenitors. We have shown that the CD4(+) T-cell expression of a novel splice isoform of Pbx1, Pbx1-d, is associated with lupus susceptibility in the NZM2410 mouse and in lupus patients. The function of Pbx1 in T cells is unknown, but the splicing out of the DNA-binding domain in Pbx1-d predicts a dominant-negative function. In support of this hypothesis, we have shown that Pbx1-d transduction accelerates differentiation of MC3T3-E1 osteoblast pregenitors and mimics the effect of short hairpin RNA silencing of Pbx1. Conversely, Pbx1-d transduction reduced the expression of Sox3, a gene strongly transactivated by Pbx1, and Pbx1-d did not bind the Sox3 promoter. These results constitute a first step towards the understanding on how Pbx1-d contributes to systemic autoimmunity in the NZM2410 mouse model as well as in lupus patients.

Role of MHC-linked susceptibility genes in the pathogenesis of human and murine lupus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies against nuclear antigens and a systemic inflammation that can damage a broad spectrum of organs. SLE patients suffer from a wide variety of symptoms, which can affect virtually almost any tissue. As lupus is difficult to diagnose, the worldwide prevalence of SLE can only be roughly estimated to range from 10 and 200 cases per 100,000 individuals with dramatic differences depending on gender, ethnicity, and location. Although the treatment of this disease has been significantly ameliorated by new therapies, improved conventional drug therapy options, and a trained expert eye, the underlying pathogenesis of lupus still remain widely unknown. The complex etiology reflects the complex genetic background of the disease, which is also not well understood yet. However, in the past few years advances in lupus genetics have been made, notably with the publication of genome-wide association studies (GWAS) in humans and the identification of susceptibility genes and loci in mice. This paper reviews the role of MHC-linked susceptibility genes in the pathogenesis of systemic lupus erythematosus.

Murine lupus susceptibility locus Sle1c2 mediates CD4+ T cell activation and maps to estrogen-related receptor γ

Sle1c is a sublocus of the NZM2410-derived Sle1 major lupus susceptibility locus. We have shown previously that Sle1c contributes to lupus pathogenesis by conferring increased CD4(+) T cell activation and increased susceptibility to chronic graft-versus-host disease (cGVHD), which mapped to the centromeric portion of the locus. In this study, we have refined the centromeric sublocus to a 675-kb interval, termed Sle1c2. Mice from recombinant congenic strains expressing Sle1c2 exhibited increased CD4(+) T cell intrinsic activation and cGVHD susceptibility, similar to mice with the parental Sle1c. In addition, B6.Sle1c2 mice displayed a robust expansion of IFN-γ-expressing T cells. NZB complementation studies showed that Sle1c2 expression exacerbated B cell activation, autoantibody production, and renal pathology, verifying that Sle1c2 contributes to lupus pathogenesis. The Sle1c2 interval contains two genes, only one of which, Esrrg, is expressed in T cells. B6.Sle1c2 CD4(+) T cells expressed less Esrrg than B6 CD4(+) T cells, and Esrrg expression was correlated negatively with CD4(+) T cell activation. Esrrg encodes an orphan nuclear receptor that regulates oxidative metabolism and mitochondrial functions. In accordance with reduced Esrrg expression, B6.Sle1c2 CD4(+) T cells present reduced mitochondrial mass and altered mitochondrial functions as well as altered metabolic pathway utilization when compared with B6 CD4(+) T cells. Taken together, we propose Esrrg as a novel lupus susceptibility gene regulating CD4(+) T cell function through their mitochondrial metabolism.

Pre-B cell leukemia homeobox 1 is associated with lupus susceptibility in mice and humans

Sle1a.1 is part of the Sle1 susceptibility locus, which has the strongest association with lupus nephritis in the NZM2410 mouse model. In this study, we show that Sle1a.1 results in the production of activated and autoreactive CD4(+) T cells. Additionally, Sle1a.1 expression reduces the peripheral regulatory T cell pool, as well as induces a defective response of CD4(+) T cells to the retinoic acid expansion of TGF-β-induced regulatory T cells. At the molecular level, Sle1a.1 corresponds to an increased expression of a novel splice isoform of Pbx1, Pbx1-d. Pbx1-d overexpression is sufficient to induce an activated/inflammatory phenotype in Jurkat T cells and to decrease their apoptotic response to retinoic acid. PBX1-d is expressed more frequently in the CD4(+) T cells from lupus patients than from healthy controls, and its presence correlates with an increased central memory T cell population. These findings indicate that Pbx1 is a novel lupus susceptibility gene that regulates T cell activation and tolerance.

Regulatory T-cell-associated cytokines in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production, complement activation, and immune complex deposition, resulting in tissue and organ damage. An understanding of the mechanisms responsible for homeostatic control of inflammation, which involve both innate and adoptive immune responses, will enable the development of novel therapies for SLE. Regulatory T cells (Treg) play critical roles in the induction of peripheral tolerance to self- and foreign antigens. Naturally occurring CD4⁺CD25⁺ Treg, which characteristically express the transcription factor forkhead box protein P3 (Foxp3), have been intensively studied because their deficiency abrogates self-tolerance and causes autoimmune disease. Moreover, regulatory cytokines such as interleukin-10 (IL-10) also play a central role in controlling inflammatory processes. This paper focuses on Tregs and Treg-associated cytokines which might regulate the pathogenesis of SLE and, hence, have clinical applications.

Elevated circulating CD4+ ICOS+ Foxp3+ T cells contribute to overproduction of IL-10 and are correlated with disease severity in patients with systemic lupus erythematosus

In this work, we aimed to investigate the frequency, possible categories and clinical significance of circulating CD4+ ICOS+ FoxP3+ T cells in patients with systemic lupus erythematosus (SLE). The frequency of circulating CD4+ ICOS+ FoxP3+ T cells was analysed by flow-cytometric analysis in 32 SLE patients, 10 rheumatoid arthritis patients and 32 healthy controls. Production of IL-10 and mTGF-β by different CD4+ T-cell populations was determined by intracellular cytokine staining. Plasma levels of IL-10 and TGF-β were determined by enzyme-linked immunosorbent assay (ELISA). The frequency of circulating CD4+ ICOS+ FoxP3+ T cells was significantly increased in SLE patients as compared with control groups. The elevated frequency of CD4+ ICOS+ FoxP3+ T cells had a positive correlation with SLE Disease Activity Index (SLEDAI) scores and serum anti-dsDNA but a negative correlation with serum C3. Additionally, the CD4+ ICOS+ Foxp3+ T cells contained significantly higher percentages of IL-10-producing cells than CD4+ ICOS- Foxp3+ T cells. A significant positive correlation was also observed between the frequency of CD4+ ICOS+ Foxp3+ T cells and the plasma level of IL-10 in SLE patients. In conclusion, an increased frequency of circulating CD4+ ICOS+ Foxp3+ T cells was observed in patients with SLE, suggesting its potential importance in the immunopathogenesis of SLE. Analysis of the CD4+ ICOS+ FoxP3+ T-cell population may be useful for the evaluation of lupus disease severity.

Regulatory T-cells in systemic lupus erythematosus and rheumatoid arthritis

Regulatory T-cells (Tregs) are the guardians of peripheral tolerance acting to prevent autoimmune diseases such as systemic lupus erythomatosus (SLE) and rheumatoid arthritis (RA). Defects in Tregs have been reported in these two diseases despite significant differences in their clinical phenotype and pathogenesis. In both diseases the potency of Treg fails to keep pace with the activation of effector cells and are unable to resist the ensuing inflammation. This review will discuss the phenotypic, numeric, and functional abnormalities in Tregs and their role in patients and murine models of SLE and RA.

Defective response of CD4(+) T cells to retinoic acid and TGFβ in systemic lupus erythematosus

Introduction

CD25⁺ FOXP3⁺ CD4⁺ regulatory T cells (Tregs) are induced by transforming growth factor β (TGFβ) and further expanded by retinoic acid (RA). We have previously shown that this process was defective in T cells from lupus-prone mice expressing the novel isoform of the Pbx1 gene, Pbx1-d. This study tested the hypothesis that CD4⁺ T cells from systemic lupus erythematosus (SLE) patients exhibited similar defects in Treg induction in response to TGFβ and RA, and that PBX1-d expression is associated with this defect.

Methods

Peripheral blood mononuclear cells (PBMCs) were collected from 142 SLE patients and 83 healthy controls (HCs). The frequency of total, memory and naïve CD4⁺ T cells was measured by flow cytometry on fresh cells. PBX1 isoform expression in purified CD4⁺ T cells was determined by reverse transcription polymerase chain reaction (RT-PCR). PBMCs were stimulated for three days with anti-CD3 and anti-CD28 in the presence or absence of TGFβ and RA. The expression of CD25 and FOXP3 on CD4⁺ T cells was then determined by flow cytometry. In vitro suppression assays were performed with sorted CD25⁺ and CD25^- FOXP3⁺ T cells. CD4⁺ T cell subsets or their expansion were compared between patients and HCs with two-tailed Mann-Whitney tests and correlations between the frequencies of two subsets were tested with Spearman tests.

Results

The percentage of CD25^- FOXP3⁺ CD4⁺ (CD25^- Tregs) T cells was greater in SLE patients than in HCs, but these cells, contrary to their matched CD25⁺ counterparts, did not show a suppressive activity. RA-expansion of TGFβ-induced CD25⁺ Tregs was significantly lower in SLE patients than in HCs, although SLE Tregs expanded significantly more than HCs in response to either RA or TGFβ alone. Defective responses were also observed for the SLE CD25^- Tregs and CD25⁺ FOXP3^- activated CD4⁺ T cells as compared to controls. PBX1-d expression did not affect Treg induction, but it significantly reduced the expansion of CD25^- Tregs and prevented the reduction of the activated CD25⁺ FOXP3^- CD4⁺ T cell subset by the combination of TGFβ and RA.

Conclusions

We demonstrated that the induction of Tregs by TGFβ and RA was defective in SLE patients and that PBX1-d expression in CD4⁺ T cells is associated with an impaired regulation of FOXP3 and CD25 by TGFβ and RA on these cells. These results suggest an impaired integration of the TGFβ and RA signals in SLE T cells and implicate the PBX1 gene in this process.

HLA DRB1*1503 allelic haplotype predominance and associated immunodysregulation in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic, relapsing, and remitting disease affecting primarily African American females of child bearing age. Familial aggregation of this disease suggests that at least part of the susceptibility for this disease is genetic, although environmental and hormonal influences are also likely to play a role. Early studies of genetic susceptibility to SLE revealed several of the major histocompatibility complex molecules, namely HLA DR, to be linked to SLE. Meta-analysis of genome scans has yielded loci significant for lupus patients, one of which includes the MHC region. Regulatory T cells are immunoregulatory cells that modulate activated immune cells. These cells play a large role in homeostasis of the immune responses and maintenance of immunologic tolerance, i.e., prevention of autoimmunity. Decreased numbers of regulatory T cells have been described in many autoimmune diseases, including systemic lupus erythematosus. Autoantibody production in systemic lupus erythematosus and the resulting immune complex formation and complex deposition into tissues are arguably the central core of immune dysregulation leading to disease manifestations and symptoms. Inability of the immune system to recognize and inhibit autoreactive immune cells in this particular autoimmune disease may be the result of inappropriate numbers and function of regulatory T cells. This study aims to characterize the immune cell population in patients from our community suffering from systemic lupus erythematosus and to prove that these patients exhibit a unique cellular profile compared to healthy age, race and gender matched control subjects. Surprisingly, our findings demonstrate that patients from the local Mississippi area exhibit increased proportions of CD25(+) FoxP3(+) regulatory T cells and CD25(+) FoxP3(-) T cells (of CD45(+) CD3(+) CD4(+) helper T cells) as compared to healthy controls. HLA tissue-typing of these lupus patients revealed a prominent subgroup (~30%) of patients possessing the HLA DRB1*1503 allele. The investigation of this subgroup demonstrated regulatory T cell composition similar to that of the total lupus group and to that of the non-HLA DRB1*1503 subgroup. Genetic analysis for molecular gene expression levels of various lupus-associated genes by real-time PCR demonstrated a unique profile as compared to healthy controls. Increased gene expression of FoxP3 together with decreased gene expression levels of GATA3, TNFAIP3, and TNFSF4 suggest that variations in gene products compared to healthy controls may be playing a role in the immune cell dysregulation and disproportionate CD25(+) FoxP3(+) regulatory T cells.

A novel isoform of the Ly108 gene ameliorates murine lupus

The expression of the new Ly108 isoform H1 weakens lupus-like disease of C57BL/6.Sle1b mice.

Studies of human systemic lupus erythematosus patients and of murine congenic mouse strains associate genes in a DNA segment on chromosome 1 with a genetic predisposition for this disease. The systematic analysis of lupus-prone congenic mouse strains suggests a role for two isoforms of the Ly108 receptor in the pathogenesis of the disease. In this study, we demonstrate that Ly108 is involved in the pathogenesis of lupus-related autoimmunity in mice. More importantly, we identified a third protein isoform, Ly108-H1, which is absent in two lupus-prone congenic animals. Introduction of an Ly108-H1–expressing transgene markedly diminishes T cell–dependent autoimmunity in congenic B6.Sle1b mice. Thus, an immune response–suppressing isoform of Ly108 can regulate the pathogenesis of lupus.

Galectin-1-induced down-regulation of T lymphocyte activation protects (NZB x NZW) F1 mice from lupus-like disease

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by a hyperactive immune system, including activation of autoreactive T and B cells. These studies demonstrate that administration of recombinant galectin-1, a β-galactose binding protein, to SLE-prone (NZB × NZW) F1 mice reduced lymphocyte activation, inhibited serum anti-double-stranded DNA(dsDNA) IgG antibody production, decreased the incidence of proteinuria, and increased survival rate. In addition, recombinant galectin-1'-treated mice had a higher frequency of Foxp3 expression, which suggested an increase in the percentage of peripheral regulatory T cells. Consistent with the finding that there were fewer activated T lymphocytes, ex vivo T cells from mice treated with recombinant galectin-1 exhibited less proliferation in response to TCR stimulation. Furthermore, these cells were less efficient at lipid raft clustering in response to TCR/CD28 engagement, consistent with published reports that galectin-1 can reorganize the synaptic contact to interfere with TCR signaling and activation to prevent T cell activation. Aged galectin-1-deficient mice had higher serum levels of antibodies against dsDNA, elucidating a role for endogenous galectin-1 in decreasing susceptibility to autoimmunity. Together, the findings highlight galectin-1 as a novel potential therapeutic immune modulator for treatment of lupus-like disease.

A New Zealand Black-derived locus suppresses chronic graft-versus-host disease and autoantibody production through nonlymphoid bone marrow-derived cells

The development of lupus pathogenesis results from the integration of susceptibility and resistance genes. We have used a chronic graft-versus-host disease (cGVHD) model to characterize a suppressive locus at the telomeric end of the NZM2410-derived Sle2 susceptibility locus, which we named Sle2c2. cGVHD is induced normally in Sle2c2-expressing mice, but it is not sustained. The analysis of mixed bone marrow chimeras revealed that cGVHD resistance was eliminated by non-B non-T hematopoietic cells expressing the B6 allele, suggesting that resistance is mediated by this same cell type. Furthermore, Sle2c2 expression was associated with an increased number and activation of the CD11b(+) GR-1(+) subset of granulocytes before and in the early stage of cGVHD induction. We have mapped the Sle2c2 critical interval to a 6-Mb region that contains the Cfs3r gene, which encodes for the G-CSFR, and its NZM2410 allele carries a nonsynonymous mutation. The G-CSFR-G-CSF pathway has been previously implicated in the regulation of GVHD, and our functional data on Sle2c2 suppression suggest a novel regulation of T cell-induced systemic autoimmunity through myeloid-derived suppressor cells. The validation of Csf3r as the causative gene for Sle2c2 and the further characterization of the Sle2c2 MDSCs promise to unveil new mechanisms by which lupus pathogenesis is regulated.

Harnessing regulatory T cells for the therapy of lupus and other autoimmune diseases

Regulatory T cells (Tregs) maintain immunological homeostasis and prevent autoimmunity. The depletion or functional alteration of Tregs may lead to the development of autoimmune diseases. Tregs consist of different subpopulations of cells, of which CD4(+)CD25(+)Foxp3(+) cells are the most well characterized. However, CD8 Tregs also constitute a major cell population that has been shown to play an important role in autoimmune diseases. This review will discuss the role of Tregs in autoimmune diseases in general and specifically in systemic lupus erythematosus (SLE). SLE is a multisystem autoimmune disease characterized by the production of autoantibodies against nuclear components and by the deposition of immune complexes in the kidneys as well as in other organs. Abnormalities in Tregs were reported in SLE patients and in animal models of the disease. Current treatment of SLE is based on immunosuppressive drugs that are nonspecific and may cause adverse effects. Therefore, the development of novel, specific, side effect-free therapeutic means that will induce functional Tregs is a most desirable goal. Our group and others have designed and utilized tolerogenic peptides that ameliorate SLE manifestations in murine models. Here, we demonstrate the role of CD4 and CD8 Tregs, as well as the interaction between the two subsets of cells and the mechanism of action of the tolerogenic peptides. We also discuss their therapeutic potential for the treatment of SLE.

Autoreactive marginal zone B cells enter the follicles and interact with CD4+ T cells in lupus-prone mice

BACKGROUND

Marginal zone B cells have been implicated in the production of autoantibodies in murine models of lupus. It has been suggested that they contribute to lupus immunopathogenesis through their enhanced effector functions and their repertoire that is biased toward autoreactive specificities. In the B6.NZM2410.Sle.Sle2.Sle3 (B6.TC) model of lupus, the majority of marginal zone B cells are located outside the marginal zone and inside the follicles. Genetic alterations of this strain have shown a correlation between autoimmune pathogenesis and the presence of intrafollicular marginal zone B cells. This study was designed first to strengthen our original observations and to determine how the marginal zone B cells from the lupus-prone mice respond to stimulations and interact with T cells.

RESULTS

The intrafollicular location of B6.TC MZB cells starts before disease manifestations and puts MZB cells in direct contact with CD4+ T cells. Two different autoreactive B cell receptor (BCR) transgenic models showed that the expression of the Sle susceptibility loci enhances the presence of MZB cells inside the follicles. In vitro, B6.TC MZB cells were better effectors than B6 MZB cells with enhanced proliferation and antibody (Ab) production, including anti-DNA Ab, in response to stimulation with TLR ligands, immune complexes or anti-CD40. Furthermore, B6.TC MZB and CD4+ T cells showed a reciprocally enhanced activation, which indicated that their contacts inside B6.TC follicles have functional consequences that suggest an amplification loop between these two cell types.

CONCLUSIONS

These results showed that the NZM2410 susceptibility loci induce MZB cells to locate into the follicles, and that this breach of follicular exclusion occurs early in the development of the autoimmune pathogenesis. The enhanced responses to stimulation and increased effector functions of MZB cells from lupus-prone mice as compare to non-autoimmune MZB cells provide a mechanism by which the failure of MZB cell follicular exclusion contributes to the autoimmune process.

Association of single-nucleotide polymorphisms in FOXP3 gene with systemic lupus erythematosus susceptibility: a case-control study

Foxp3, encoded by the human FOXP3 gene, is a transcription factor that regulates regulatory T-cell (Treg) development and function. Associations have been reported between FOXP3 gene variants and autoimmune endocrinopathy and non-endocrine autoimmune disease. The aim of this study was to investigate the possible influence of single nucleotide polymorphisms (SNP) in the FOXP3 gene on genetic predisposition to systemic lupus erythematosus (SLE). The study cohort comprised 172 SLE patients and 181 controls, who were genotyped for the FOXP3 gene variants. Of five SNPs identified, the FOXP3 -6054 ATT carrier was shown to be associated with renal disorder (odds ratio [OR] 3.26, 95% confidence interval [95% CI] 1.33-8.03, p = 0.0077). Furthermore, lower anti-dsDNA levels were found in patients with the -3279 A carrier (p = 0.0109). To the authors' knowledge, this is the first study to investigate the association of FOXP3 SNPs with susceptibility to SLE, as well as sub-phenotype susceptibility. Although the exact role of Foxp3 and FOXP3 gene variations in SLE is still not clear, the present data support the importance of variations in the FOXP3 gene region for the etiology of certain manifestations of SLE.

Constitutive overexpression of BAFF in autoimmune-resistant mice drives only some aspects of systemic lupus erythematosus-like autoimmunity

OBJECTIVE

To determine whether overexpression of BAFF can promote systemic lupus erythematosus (SLE)-like autoimmunity in mice that are otherwise autoimmune-resistant.

METHODS

We used class II major histocompatibility complex (MHC)-deficient C57BL/6 (B6) mice as a model of resistance to SLE and Sles1-bearing B6 mice as a model of resistance to the autoantibody-promoting capacity of the Sle1 region. We generated BAFF-transgenic (Tg) counterparts to these respective mice and evaluated lymphocyte phenotype, serologic autoimmunity, renal immunopathology, and clinical disease in the BAFF-Tg and non-Tg mouse sets.

RESULTS

Although constitutive BAFF overexpression did not lead to B cell expansion in class II MHC-deficient B6 mice, it did lead to increased serum IgG autoantibody levels. Nevertheless, renal immunopathology was limited, and clinical disease did not develop. In B6 and B6.Sle1 mice, constitutive BAFF overexpression led to increased numbers of B cells and CD4+ memory cells, as well as increased serum IgG and IgA autoantibody levels. Renal immunopathology was modestly greater in BAFF-Tg mice than in their non-Tg counterparts, but again, clinical disease did not develop. Introduction of the Sles1 region into B6.Sle1.Baff mice abrogated the BAFF-driven increase in CD4+ memory cells and the Sle1-driven, but not the BAFF-driven, increase in serum IgG antichromatin levels. Renal immunopathology was substantially ameliorated.

CONCLUSION

Although constitutive BAFF overexpression in otherwise autoimmune-resistant mice led to humoral autoimmunity, meaningful renal immunopathology and clinical disease did not develop. This raises the possibility that BAFF overexpression, even when present, may not necessarily drive disease in some SLE patients. This may help explain the heterogeneity of the clinical response to BAFF antagonists in human SLE.

Murine lupus susceptibility locus Sle1a requires the expression of two sub-loci to induce inflammatory T cells

The NZM2410-derived Sle1a lupus susceptibility locus induces activated autoreactive CD4⁺ T cells and reduces the number and function of Foxp3⁺ regulatory T cells. In this study, we first showed that Sle1a contributes to autoimmunity by increasing anti-nuclear antibody production when expressed on either NZB or NZW heterozygous genomes, and by enhancing the chronic graft vs. host disease response indicating an expansion of the autoreactive B cell pool. Screening two non-overlapping recombinants, the Sle1a.1 and Sle1a.2 intervals that cover the entire Sle1a locus, revealed that both Sle1a.1 and Sle1a.2 were necessary for the full Sle1a phenotype. Sle1a.1, and to a lesser extent Sle1a.2, significantly affected CD4⁺ T cell activation as well as Treg differentiation and function. Sle1a.2 also increased the production of autoreactive B cells. Since the Sle1a.1 and Sle1a.2 intervals contain only one and 15 known genes, respectively, this study considerably reduces the number of candidate genes responsible for the production of autoreactive T cells. These results also demonstrate that the Sle1 locus is an excellent model for the genetic architecture of lupus, in which a major obligate phenotype results from the co-expression of multiple genetic variants with individual weak effects.

Identification and characterization of a lupus suppressor 129 locus on chromosome 3

The 129-derived Sle16 is a susceptibility locus for systemic autoimmunity when present on the C57BL/6 (B6) background. Genetic analysis of a (129xB6)F2 cross identified a region from the B6 chromosome 3 (Sle18) with positive linkage to antinuclear Abs. In this study, we have generated a B6 congenic strain harboring the 129 allele of Sle18 and intercrossed this line with the lupus-prone B6.129-Sle16 strain. The presence of the 129-Sle18 allele in the B6.129-Sle16Sle18 double congenic mice suppressed the development of Sle16-mediated autoantibody production and ameliorated the renal pathology. The 129-Sle18 locus rectified the B cell abnormalities detected in the B6.129-Sle16 mice, such as the reduction in the percentage of marginal zone B and B1a cells and the increased number of germinal centers. The B6.129-Sle16Sle18 spleens still displayed an increased percentage of activated T and B cells. However, in the B6.129-Sle16Sle18 strain the percentage of naive T cells was equivalent to that in B6.129-Sle18 and B6 mice and these cells showed a reduced proliferative response to anti-CD3 stimulation compared with B6.129-Sle16 T cells. There was a significant increase in the percentage of CD4(+)FoxP3(+)regulatory T cells in all congenic strains. These cells had normal regulatory function when tested in vitro. Thus, 129-Sle18 represents a novel, non-MHC lupus-suppressor locus probably operating as a functional modifier of B cells that, in combination with other factors, leads to lupus resistance. Further characterization of this locus will help to uncover the immune mechanism(s) conferring protection against lupus.

Experimental extracorporeal photopheresis therapy significantly delays the development of diabetes in non-obese diabetic mice

In our previous studies, we demonstrated that infusion of apoptotic cells significantly prevented type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. Extracorporeal photopheresis (ECP) is an apoptotic cell-based therapy used clinically for immune-mediated disorders. In this study, we examined the effect that intravenous delivery of apoptotic cells (ECP-treated) has in the prevention of T1D in NOD mice. We discovered that five weekly injections of ECP-treated NOD spleen cells, beginning at 8 weeks of age, significantly delayed diabetes onset. Furthermore, cell dose studies demonstrated that low dose ECP-treated spleen cells (2x10(5) cells/injection/mouse) had similar protective effects as compared to high dose (5x10(6) cells/injection). In contrast to ECP-treated cells alone, ECP-treated cells combined with beta cell antigens appeared to improve the protective effect as shown by the marked reduction in insulitis in the islets. Delivery of ECP-treated spleen cells or ECP-treated spleen cells plus beta cell antigen increased Foxp3(+) Tregs, and beta cell antigen-specific T cell proliferation was significantly suppressed in vivo in these two groups. In addition, we found that ECP-treated cells did not induce global immunosuppression or autoimmunity against nuclear antigens. In conclusion, ECP-treated cells provide a safe and effective approach in T1D prevention, suggesting that clinical ECP has great potential for managing human T1D.