Partial Protection From Lupus-Like Disease by B-Cell Specific Type I Interferon Receptor Deficiency

Systemic lupus erythematosus (SLE) is an autoimmune disease that can present with many different permutations of symptom presentation. A large subset of SLE patients have been shown to present with elevated interferon stimulated gene (ISG) expression, and Type I IFNs (IFNαβ) have been shown to drive disease in murine models through global IFNα Receptor (IFNAR) knockouts. However, the disease contribution of distinct immune cell subsets in response to constitutively increased levels of IFNαβ is not fully understood. We utilized a B-cell specific IFNAR knockout (BΔIFNAR) on the B6.Nba2 spontaneous-lupus background to determine the contribution of IFNαβ stimulated B cells in disease. We found that IFNαβ signaling in B cells is driving increased splenomegaly, increased populations of activated B cells, and increased populations of germinal center (GC) B cells, memory B cells, and plasma blasts/cells, but did not affect the development of glomerulonephritis and immune-complex deposition. IFNAR expression by B cells also drove production of anti-chromatin IgG, and anti-dsDNA and -nRNP IgG and IgG_2C auto-antibody levels, as well as increased Bcl2 expression, affecting GC B cell survival in B6.Nba2 mice.

Androgen-Mediated Anti-inflammatory Cellular Processes as Therapeutic Targets in Lupus

Systemic Lupus Erythematosus (SLE), among many other auto-immune diseases, is known to be more prevalent in females than in males. This observation has served as the foundation for studies into how sex hormones may interact with the immune system to either drive or inhibit immune activation. Early studies using castration in lupus mouse models showed the potential protective effect of testosterone against lupus development. These studies were later corroborated by observational studies in lupus patients, who upon treatment with testosterone therapy, displayed decreased disease burden. However, there are numerous limitations to treating (especially female) lupus patients with testosterone. Thus, identification of testosterone-targeted cellular and molecular mechanisms affecting immune activation is an attractive target for lupus treatment in the future. Recent studies have examined the effects of androgens on the activation of anti-inflammatory processes. As such, immunoregulatory cell types including myeloid-derived suppressor cells (MDSCs) and regulatory T and B cells have been shown to be susceptible to manipulation by sex hormones. Here, we review studies of SLE and lupus-like disease in which testosterone or testosterone-derivatives were used to skew an ongoing immune reaction toward an anti-inflammatory state. Via evaluation of both clinical studies and immunologic models we propose new areas for research with the goal of identifying testosterone-driven anti-inflammatory mediators suitable for therapeutic targeting in patients with lupus and other autoimmune diseases.

Low Levels of Vitamin D Promote Memory B Cells in Lupus

Background: Vitamin D deficiency is a known risk factor for Systemic Lupus Erythematosus (SLE), yet clinical trials have not demonstrated efficacy and few studies have utilized lupus models to understand the mechanism underlying this relationship. The Act1-/- mouse is a spontaneous model of lupus and Sjögren's syndrome, characterized by increased Th17 cells and peripheral B cell expansion. Vitamin D3 has anti-inflammatory properties, reduces Th17 cells and impairs B cell differentiation/activation. Therefore, we assessed how varying amounts of vitamin D3 affected lupus-like disease in the Act1-/- mouse. Methods: Act1-/- mice were fed either low/restricted (0 IU/kg), normal (2 IU/kg), or high/supplemented (10 IU/kg) vitamin D3 chow for 9 weeks, after which lupus-like features were analyzed. Results: While we found no differences in Th17 cells between vitamin D3 groups, vitamin D3 restriction specifically promoted memory B cell development, accompanied by elevated levels of serum IgM, IgG1, IgG3, and anti-dsDNA IgG. A similar significant negative association between serum vitamin D and memory B cells was confirmed in a cohort of SLE patients. Conclusion: Low levels of vitamin D3 are associated with elevated levels of memory B cells in an animal model of lupus and well-controlled SLE patients.

Relationships Between Vitamin D, Gut Microbiome, and Systemic Autoimmunity

There is increasing recognition of the role the microbiome plays in states of health and disease. Microbiome studies in systemic autoimmune diseases demonstrate unique microbial patterns in Inflammatory Bowel Disease, Rheumatoid Arthritis, and Systemic Lupus Erythematosus to a lesser extent, whereas there is no single bug or pattern that characterizes Multiple Sclerosis. Autoimmune diseases tend to share a predisposition for vitamin D deficiency, which alters the microbiome and integrity of the gut epithelial barrier. In this review, we summarize the influence of intestinal bacteria on the immune system, explore the microbial patterns that have emerged from studies on autoimmune diseases, and discuss how vitamin D deficiency may contribute to autoimmunity via its effects on the intestinal barrier function, microbiome composition, and/or direct effects on immune responses.

Limited Effect of Indolamine 2,3-Dioxygenase Expression and Enzymatic Activity on Lupus-Like Disease in B6.Nba2 Mice

B6.Nba2 mice spontaneously develop a lupus-like disease characterized by elevated levels of serum anti-nuclear autoantibody (ANA) immune complexes and constitutive type I interferon (IFNα) production. During disease progression, both plasmacytoid dendritic cells (pDCs) and antibody secreting plasma cells accumulate in spleens of B6.Nba2 mice. Indoleamine 2,3-dioxygenase (IDO) has been suggested to play a role in several autoimmune diseases including in the MRL/lpr model of mouse lupus-like disease; however, it remains unknown if IDO is involved in disease development and/or progression in other spontaneous models. We show here that IDO1 protein and total IDO enzymatic activity are significantly elevated in lupus-prone B6.Nba2 mice relative to B6 controls. IDO1 expression was restricted to PCs and SignR1⁺ macrophages in both strains, while significantly increased in B6.Nba2-derived SiglecH⁺ (SigH⁺) pDCs. Despite this unique expression pattern, neither pharmacologic inhibition of total IDO nor IDO1 gene ablation altered serum autoantibody levels, splenic immune cell activation pattern, or renal inflammation in B6.Nba2 mice. Interestingly, IDO pharmacologic inhibition, but not IDO1 deficiency, resulted in diminished complement factor C'3 fixation to kidney glomeruli, suggesting a possible therapeutic benefit of IDO inhibition in SLE patients with renal involvement.

Immunological effects of vitamin D and their relations to autoimmunity

Vitamin D deficiency is an established risk factor for many autoimmune diseases and the anti-inflammatory properties of vitamin D underscore its potential therapeutic value for these diseases. However, results of vitamin D3 supplementation clinical trials have been varied. To understand the clinical heterogeneity, we reviewed the pre-clinical data on vitamin D activity in four common autoimmune diseases: multiple sclerosis (MS), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD), in which patients are commonly maintained on oral vitamin D3 supplementation. In contrast, many pre-clinical studies utilize other methods of manipulation (i.e. genetic, injection). Given the many actions of vitamin D3 and data supporting a vitamin D-independent role of the Vitamin D receptor (VDR), a more detailed mechanistic understanding of vitamin D3 activity is needed to properly translate pre-clinical findings into the clinic. Therefore, we assessed studies based on route of vitamin D3 administration, and identified where discrepancies in results exist and where more research is needed to establish the benefit of vitamin D supplementation.

Act1 is a negative regulator in T and B cells via direct inhibition of STAT3

Although Act1 (adaptor for IL-17 receptors) is necessary for IL-17-mediated inflammatory responses, Act1- (but not Il17ra-, Il17rc-, or Il17rb-) deficient mice develop spontaneous SLE- and Sjögren's-like diseases. Here, we show that Act1 functions as a negative regulator in T and B cells via direct inhibition of STAT3. Mass spectrometry analysis detected an Act1-STAT3 complex, deficiency of Act1 (but not Il17ra-, Il17rc-, or Il17rb) results in hyper IL-23- and IL-21-induced STAT3 activation in T and B cells, respectively. IL-23R deletion or blockade of IL-21 ameliorates SLE- and Sjögren's-like diseases in Act1-/- mice. Act1 deficiency results in hyperactivated follicular Th17 cells with elevated IL-21 expression, which promotes T-B cell interaction for B cell expansion and antibody production. Moreover, anti-IL-21 ameliorates the SLE- and Sjögren's-like diseases in Act1-deficient mice. Thus, IL-21 blocking antibody might be an effective therapy for treating SLE- and Sjögren's-like syndrome in patients containing Act1 mutation.

Differential Internalization Rates and Postendocytic Sorting of the Norepinephrine and Dopamine Transporters Are Controlled by Structural Elements in the N Termini

The norepinephrine transporter (NET) mediates reuptake of synaptically released norepinephrine in central and peripheral noradrenergic neurons. The molecular processes governing availability of NET in the plasma membrane are poorly understood. Here we use the fluorescent cocaine analogue JHC 1-64, as well as several other approaches, to investigate the trafficking itinerary of NET in live noradrenergic neurons. Confocal imaging revealed extensive constitutive internalization of JHC 1-64-labeled NET in the neuronal somata, proximal extensions and presynaptic boutons. Phorbol 12-myristate 13-acetate increased intracellular accumulation of JHC 1-64-labeled NET and caused a parallel reduction in uptake capacity. Internalized NET strongly colocalized with the "long loop" recycling marker Rab11, whereas less overlap was seen with the "short loop" recycling marker Rab4 and the late endosomal marker Rab7. Moreover, mitigating Rab11 function by overexpression of dominant negative Rab11 impaired NET function. Sorting of NET to the Rab11 recycling compartment was further supported by confocal imaging and reversible biotinylation experiments in transfected differentiated CATH.a cells. In contrast to NET, the dopamine transporter displayed markedly less constitutive internalization and limited sorting to the Rab11 recycling compartment in the differentiated CATH.a cells. Exchange of domains between the two homologous transporters revealed that this difference was determined by non-conserved structural elements in the intracellular N terminus. We conclude that NET displays a distinct trafficking itinerary characterized by continuous shuffling between the plasma membrane and the Rab11 recycling compartment and that the functional integrity of the Rab11 compartment is critical for maintaining proper presynaptic NET function.

Suppressive effects of androgens on the immune system

Sex-based disparities in immune responses are well known phenomena. The two most important factors accounting for the sex-bias in immunity are genetics and sex hormones. Effects of female sex hormones, estrogen and progesterone are well established, however the role of testosterone is not completely understood. Evidence from unrelated studies points to an immunosuppressive role of testosterone on different components of the immune system, but the underlying molecular mechanisms remains unknown. In this review we evaluate the effect of testosterone on key cellular components of innate and adaptive immunity. Specifically, we highlight the importance of testosterone in down-regulating the systemic immune response by cell type specific effects in the context of immunological disorders. Further studies are required to elucidate the molecular mechanisms of testosterone-induced immunosuppression, leading the way to the identification of novel therapeutic targets for immune disorders.

Gr1+ cells suppress T-dependent antibody responses in (NZB x NZW)F1 male mice through inhibition of T follicular helper cells and germinal center formation

Systemic lupus erythematosus is an autoimmune disease characterized by elevated production of autoreactive Abs. The disease has a much higher prevalence in women than in men. Although testosterone has been shown to be protective in the disease, and estrogens exacerbating, the discrepancy in prevalence between men and women is still not well understood and the mechanism behind it is unknown. We have recently described that male (New Zealand black [NZB] × New Zealand white [NZW])F1 mice have higher levels of Gr1(+)CD11b(+) cells, and that these cells suppress autoantibody production in vivo. In this article, we extend our findings to show that similarly to humans, female lupus-prone (NZB × NZW)F1 mice also respond with stronger Ab responses to thymus-dependent Ag immunization than male littermates. Furthermore, the presence or absence of Gr1-expressing cells not only control Ag-specific Ab responses in male, but not female, (NZB × NZW)F1 mice, but also significantly alter the activation and differentiation of CD4(+) T cells in vitro and in vivo. In particular, we found that Gr1(+) cells from male (NZB × NZW)F1 mice suppress the differentiation and effector function of CXCR5(+)PD-1(+) T follicular helper cells, thereby controlling germinal center formation and plasma cell differentiation. This new finding strongly supports efforts to develop new drugs that target myeloid cell subsets in a number of T and B cell-mediated diseases with a female predominance.

Spontaneous loss of tolerance of autoreactive B cells in Act1-deficient rheumatoid factor transgenic mice

Self-reactive B cells in BALB/c AM14 transgenic (Tg) rheumatoid factor mice are not subject to central or peripheral tolerization. Instead, they remain at a stage of "clonal ignorance"; that is, they do not proliferate and differentiate into Ab-forming cells. However, the immunoregulatory mechanisms that prevent autoantibody production in these mice remain unclear. In this study, we show that crossing AM14 Tg mice to a mouse strain deficient in Act1, a molecule involved in the regulation of BAFF-R and CD40-signaling in B cells, results in spontaneous activation of AM14 Tg B cells and production of AM14-specific Abs. Three- to 5-mo-old AM14 Tg Act1(-/-) mice showed significant expansion of AM14 Tg B cells, including a 2- to 3-fold increase in the spleen and cervical lymph nodes compared with AM14 Tg Act1(+/+) mice. Furthermore, in the presence of endogenous self-Ag (IgH(a) congenic background), AM14 Tg Act1(-/-) B cells were spontaneously activated and differentiated into Ab-forming cells. In contrast with previous studies using AM14 Tg MLR.Fas(lpr) mice, we found that a significant number of AM14 Tg cells AM14 Tg Act1(-/-) mice displayed phenotypic characteristics of germinal center B cells. Anti-CD40L treatment significantly limited the expansion and activation of AM14 Tg Act1(-/-) B cells, suggesting that CD40L-mediated signals are required for the retention of these cells. Our results support the important role of Act1 in the regulation of self-reactive B cells and reveal how Act1 functions to prevent the production of autoantibodies.

Intracellular and circulating neuronal antinuclear antibodies in human epilepsy

There are overwhelming data supporting the inflammatory origin of some epilepsies (e.g., Rasmussen's encephalitis and limbic encephalitis). Inflammatory epilepsies with an autoimmune component are characterized by autoantibodies against membrane-bound, intracellular or secreted proteins (e.g., voltage gated potassium channels). Comparably, little is known regarding autoantibodies targeting nuclear antigen. We tested the hypothesis that in addition to known epilepsy-related autoantigens, the human brain tissue and serum from patients with epilepsy contain autoantibodies recognizing nuclear targets. We also determined the specific nuclear proteins acting as autoantigen in patients with epilepsy. Brain tissue samples were obtained from patients undergoing brain resections to treat refractory seizures, from the brain with arteriovenous malformations or from post-mortem multiple sclerosis brain. Patients with epilepsy had no known history of autoimmune disease and were not diagnosed with autoimmune epilepsy. Tissue was processed for immunohistochemical staining. We also obtained subcellular fractions to extract intracellular IgGs. After separating nuclear antibody-antigen complexes, the purified autoantigen was analyzed by mass spectrometry. Western blots using autoantigen or total histones were probed to detect the presence of antinuclear antibodies in the serum of patients with epilepsy. Additionally, HEp-2 assays and antinuclear antibody ELISA were used to detect the staining pattern and specific presence of antinuclear antibodies in the serum of patients with epilepsy. Brain regions from patients with epilepsy characterized by blood-brain barrier disruption (visualized by extravasated albumin) contained extravasated IgGs. Intracellular antibodies were found in epilepsy (n=13/13) but not in multiple sclerosis brain (n=4/4). In the brain from patients with epilepsy, neurons displayed higher levels of nuclear IgGs compared to glia. IgG colocalized with extravasated albumin. All subcellular fractions from brain resections of patients with epilepsy contained extravasated IgGs (n=10/10), but epileptogenic cortex, where seizures originated from, displayed the highest levels of chromatin-bound IgGs. In the nuclear IgG pool, anti-histone autoantibodies were identified by two independent immunodetection methods. HEp-2 assay and ELISA confirmed the presence of anti-histone (n=5/8) and anti-chromatin antibodies in the serum from patients with epilepsy. We developed a multi-step approach to unmask autoantigens in the brain and sera of patients with epilepsy. This approach revealed antigen-bound antinuclear antibodies in neurons and free antinuclear IgGs in the serum of patients with epilepsy. Conditions with blood-brain barrier disruption but not seizures, were characterized by extravasated but not chromatin-bound IgGs. Our results show that the pool of intracellular IgG in the brain of patients with epilepsy consists of nucleus-specific autoantibodies targeting chromatin and histones. Seizures may be the trigger of neuronal uptake of antinuclear antibodies.

Lack of T cells in Act1-deficient mice results in elevated IgM-specific autoantibodies but reduced lupus-like disease

Act1 is a negative regulator of B-cell activation factor of the TNF family (BAFF) and CD40L-induced signaling. BALB/C mice lacking Act1 develop systemic autoimmunity resembling systemic lupus erythematosus (SLE) and Sjögren's syndrome (SjS). SLE and SjS are characterized by anti-nuclear IgG autoantibody (ANA-IgG) production and inflammation of peripheral tissues. As autoantibody production can occur in a T-cell dependent or T-cell independent manner, we investigated the role of T-cell help during Act1-mediated autoimmunity. Act1-deficiency was bred onto C57Bl/6 (B6.Act1(-/-) ) mice and B6.TCRβ(-/-) TCRδ(-/-) Act1(-/-) (TKO) mice were generated. While TCRβ/δ-sufficient B6.Act1(-/-) mice developed splenomegaly and lymphadenopathy, hypergammaglobulinemia, elevated levels of ANA-IgG, and kidney pathology, TKO mice failed to develop any such signs of disease. Neither B6.Act1(-/-) nor TKO mice developed SjS-like disease, suggesting that epigenetic interactions on the BALB/C background are responsible for this phenotype in BALB/C.Act1(-/-) mice. Interestingly, BAFF-driven transitional B-cell abnormalities, previously reported in BALB/C.Act1(-/-) mice, were intact in B6.Act1(-/-) mice and largely independent of T cells. In conclusion, T cells are necessary for the development of SLE-like disease in B6.Act1(-/-) mice, but not BAFF-driven transitional B-cell differentiation.

Brain-derived neurotrophic factor (BDNF) enhances GABA transport by modulating the trafficking of GABA transporter-1 (GAT-1) from the plasma membrane of rat cortical astrocytes

The γ-aminobutyric acid (GABA) transporters (GATs) are located in the plasma membrane of neurons and astrocytes and are responsible for termination of GABAergic transmission. It has previously been shown that brain derived neurotrophic factor (BDNF) modulates GAT-1-mediated GABA transport in nerve terminals and neuronal cultures. We now report that BDNF enhances GAT-1-mediated GABA transport in cultured astrocytes, an effect mostly due to an increase in the V(max) kinetic constant. This action involves the truncated form of the TrkB receptor (TrkB-t) coupled to a non-classic PLC-γ/PKC-δ and ERK/MAPK pathway and requires active adenosine A(2A) receptors. Transport through GAT-3 is not affected by BDNF. To elucidate if BDNF affects trafficking of GAT-1 in astrocytes, we generated and infected astrocytes with a functional mutant of the rat GAT-1 (rGAT-1) in which the hemagglutinin (HA) epitope was incorporated into the second extracellular loop. An increase in plasma membrane of HA-rGAT-1 as well as of rGAT-1 was observed when both HA-GAT-1-transduced astrocytes and rGAT-1-overexpressing astrocytes were treated with BDNF. The effect of BDNF results from inhibition of dynamin/clathrin-dependent constitutive internalization of GAT-1 rather than from facilitation of the monensin-sensitive recycling of GAT-1 molecules back to the plasma membrane. We therefore conclude that BDNF enhances the time span of GAT-1 molecules at the plasma membrane of astrocytes. BDNF may thus play an active role in the clearance of GABA from synaptic and extrasynaptic sites and in this way influence neuronal excitability.

SLC6 neurotransmitter transporters: structure, function, and regulation

The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.

The adaptor molecule Act1 regulates BAFF responsiveness and self-reactive B cell selection during transitional B cell maturation

The transitional stage is a key check-point for elimination of autoreactive B cells in the periphery. This selection process requires fine regulation of signals received through BCR and B cell activating factor (BAFF) receptor. We previously identified the adaptor molecule Act1 as a negative regulator of BAFF-mediated signaling. Deficiency of Act1 in mice results in peripheral B cell hyperplasia and development of autoimmunity. In this study, we demonstrate that Act1 plays a critical role in the regulation of transitional B cell survival and maturation. We found that the ratio of late-transitional (T2) to early-transitional (T1) cells was increased in spleens from Act1-deficient mice. Moreover, BAFF stimulation induced better T1 cell survival and promoted more efficient maturation of T1 cells into T2 cells ex vivo in the absence of Act1. BAFF stimulation induced higher levels of the anti-apoptotic Bcl-2 member Mc1-l in Act1-deficient T1 cells than in wild-type control cells, suggesting that Mcl-1 might be one of the key effector molecules for BAFF-mediated survival of the Act1-deficient transitional B cells. Importantly, costimulation with BAFF was able to rescue Act1-deficient T1 cells from BCR-induced apoptosis more effectively than Act1-sufficient T1 B cells. Finally, by using hen egg lysozyme double transgenic mice, we demonstrated that Act1 deficiency can promote the maturation of Ag-specific autoreactive B cells. Taken together, our results suggest that the transitional stage is a critical point of action of Act1 in the elimination of autoreactive B cells and in the regulation of peripheral B cell homeostasis.

The N terminus of monoamine transporters is a lever required for the action of amphetamines

The serotonin transporter (SERT) terminates neurotransmission by removing serotonin from the synaptic cleft. In addition, it is the site of action of antidepressants (which block the transporter) and of amphetamines (which induce substrate efflux). We explored the functional importance of the N terminus in mediating the action of amphetamines by focusing initially on the highly conserved threonine residue at position 81, a candidate site for phosphorylation by protein kinase C. Molecular dynamics simulations of the wild type SERT, compared with its mutations SERT^T81A and SERT^T81D, suggested structural changes in the inner vestibule indicative of an opening of the inner vestibule. Predictions from this model (e.g. the preferential accumulation of SERT^T81A in the inward conformation, its reduced turnover number, and a larger distance between its N and C termini) were verified. Most importantly, SERT^T81A (and the homologous mutations in noradrenaline and dopamine) failed to support amphetamine-induced efflux, and this was not remedied by aspartate at this position. Amphetamine-induced currents through SERT^T81A were comparable with those through the wild type transporter. Both abundant Na⁺ entry and accumulation of SERT^T81A in the inward facing conformation ought to favor amphetamine-induced efflux. Thus, we surmised that the N terminus must play a direct role in driving the transporter into a state that supports amphetamine-induced efflux. This hypothesis was verified by truncating the first 64 amino acids and by tethering the N terminus to an additional transmembrane helix. Either modification abolished amphetamine-induced efflux. We therefore conclude that the N terminus of monoamine transporters acts as a lever that sustains reverse transport.

Development of murine lupus involves the combined genetic contribution of the SLAM and FcgammaR intervals within the Nba2 autoimmune susceptibility locus

Autoantibodies are of central importance in the pathogenesis of Ab-mediated autoimmune disorders. The murine lupus susceptibility locus Nba2 on chromosome 1 and the syntenic human locus are associated with a loss of immune tolerance that leads to antinuclear Ab production. To identify gene intervals within Nba2 that control the development of autoantibody-producing B cells and to determine the cellular components through which Nba2 genes accomplish this, we generated congenic mice expressing various Nba2 intervals where genes for the FcgammaR, SLAM, and IFN-inducible families are encoded. Analysis of congenic strains demonstrated that the FcgammaR and SLAM intervals independently controlled the severity of autoantibody production and renal disease, yet are both required for lupus susceptibility. Deregulated homeostasis of terminally differentiated B cells was found to be controlled by the FcgammaR interval where FcgammaRIIb-mediated apoptosis of germinal center B cells and plasma cells was impaired. Increased numbers of activated plasmacytoid dendritic cells that were distinctly CD19+ and promoted plasma cell differentiation via the proinflammatory cytokines IL-10 and IFNalpha were linked to the SLAM interval. These findings suggest that SLAM and FcgammaR intervals act cooperatively to influence the clinical course of disease through supporting the differentiation and survival of autoantibody-producing cells.

Dissection of genetic mechanisms governing the expression of serum retroviral gp70 implicated in murine lupus nephritis

The endogenous retroviral envelope glycoprotein, gp70, implicated in murine lupus nephritis is secreted by hepatocytes as an acute phase protein, and it has been thought to be a product of an endogenous xenotropic virus, NZB-X1. However, since endogenous polytropic (PT) and modified polytropic (mPT) viruses encode gp70s that are closely related to xenotropic gp70, these viruses can be additional sources of serum gp70. To better understand the genetic basis of the expression of serum gp70, we analyzed the abundance of xenotropic, PT, or mPT gp70 RNAs in livers and the genomic composition of corresponding proviruses in various strains of mice, including two different Sgp (serum gp70 production) congenic mice. Our results demonstrated that the expression of different viral gp70 RNAs was remarkably heterogeneous among various mouse strains and that the level of serum gp70 production was regulated by multiple structural and regulatory genes. Additionally, a significant contribution of PT and mPT gp70s to serum gp70 was revealed by the detection of PT and mPT, but not xenotropic transcripts in 129 mice, and by a closer correlation of serum levels of gp70 with the abundance of PT and mPT gp70 RNAs than with that of xenotropic gp70 RNA in Sgp3 congenic mice. Furthermore, the injection of lipopolysaccharides selectively up-regulated the expression of xenotropic and mPT gp70 RNAs, but not PT gp70 RNA. Our data indicate that the genetic origin of serum gp70 is more heterogeneous than previously thought, and that distinct retroviral gp70s are differentially regulated in physiological vs inflammatory conditions.

Identification of candidate genes that influence sex hormone-dependent disease phenotypes in mouse lupus

Ninety percent of systemic lupus erythematosus patients are female, and gender differences in lupus susceptibility are also observed in (New Zealand Black x New Zealand White)F1 (BWF1) lupus-prone mice. We followed orchiectomized, intact male and female BWF1 mice for lupus-like disease for 1 year. A comparative gene expression analysis was then used to identify candidate genes potentially responsible for gender-dependent differences in lupus susceptibility. Seven genes encoded on the sex chromosomes and 77 probe sets, including 14 immunoglobulin genes, encoded on the autosomal chromosomes were identified as differentially expressed in male versus female BWF1 splenocytes prior to disease onset. Five genes were determined to be regulated by either estradiol or dihydrotestosterone in an in vivo system and most of them were preferentially expressed in antigen-presenting cells. Gender differences in the expression of Csf3-r, Histh1c, Serpinb2, Slc6a4 and Cd22 in BWF1 mice are the result of transcriptional modification by sex hormones and warrant further investigation. The identification of candidate genes and their expression patterns in splenocyte sub-populations provide new information regarding the mechanisms by which sex hormones influence the development of mouse lupus.

Type I interferon signaling is involved in the spontaneous development of lupus-like disease in B6.Nba2 and (B6.Nba2 × NZW)F1 mice

Several studies have described a role for type I interferons (IFNalphabeta) in the initiation and/or prolongation of autoimmune diseases. Most pronounced has been the association of disease activity with what is now known as 'the interferon signature' of gene expression in peripheral blood mononuclear cells from lupus patients. In correlation, studies have shown that inhibition of IFNalphabeta signaling abrogates disease in various mouse models of lupus. New Zealand black (NZB) and B6.Nba2 congenic mice spontaneously develop elevated levels of serum anti-nuclear autoantibodies (ANAs). Nevertheless, neither of these strains develop fatal renal disease. The female F1 offspring of NZB or B6.Nba2 crossed with New Zealand white (NZW) mice do, however, develop kidney disease. We have previously shown that increases in endogenous IFNalphabeta levels in (B6.Nba2 x NZW)F1 mice leads to accelerated development of renal disease in an IFNalphabeta-dependent manner. We now show that B6.Nba2 and (B6.Nba2 x NZW)F1 mice deficient for the IFNalphabeta-receptor fail to develop ANA and renal disease, although the mice have substantial immune complex deposition in the glomeruli. Thus, endogenous IFNalphabeta might influence disease by affecting B-cell activation and differentiation, as well as the kidneys' susceptibility to damage, the latter perhaps through induction of a local inflammatory milieu.

Genetic susceptibility to polyI:C-induced IFNalpha/beta-dependent accelerated disease in lupus-prone mice

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. Associations between viral infections and the onset of SLE have been suggested, and recent studies have provided evidence that type I interferons (IFNalpha/beta) might play a role in the SLE disease process. Viruses and interferons have also been implicated in mouse models of SLE. We generated a model of accelerated proteinuria, in which lupus-prone mice were injected repeatedly with polyinosinic:polycytidylic acid (polyI:C), mimicking exposure to virus-derived double stranded RNA (dsRNA), leading to the production of IFNalpha/beta. PolyI:C-treated (B6.Nba2 x NZW)F1 and (B6 x NZW)F1 hybrid mice developed significantly increased levels of anti-dsDNA autoantibodies, characteristic of lupus. Most significantly, polyI:C-treated (B6.Nba2 x NZW)F1 mice, but not (B6 x NZW)F1 or parental strains, developed lupus-like nephritis in an accelerated fashion, which was dependent on IFNalpha/beta and associated with elevated deposition of total IgG, IgG2a and complement factor C3 in the glomerular capillary walls. These data suggest that reagents, which increase the levels of endogenous IFNalpha/beta (directly or indirectly), can accelerate the course of lupus-like nephritis, the development of which is dependent on the presence of both NZW- and Nba2-encoded genes.

Increased expression of Ifi202, an IFN-activatable gene, in B6.Nba2 lupus susceptible mice inhibits p53-mediated apoptosis

Increased expression of p202 protein (encoded by the Ifi202 gene) in splenocytes derived from B6.Nba2 mice (congenic for the Nba2 interval derived from the New Zealand Black mice) was correlated with defects in apoptosis of splenic B cells and increased susceptibility to develop systemic lupus erythematosus. We have now investigated the molecular mechanisms by which increased expression of p202 in B6.Nba2 cells contributes to defects in apoptosis. In this study, we report that increased expression of p202 in the B6.Nba2 splenocytes, as compared with cells derived from the parental C57BL/6 (B6) mice, was correlated with increased levels of p53 protein and inhibition of p53-mediated transcription of target genes that encode proapoptotic proteins. Conversely, knockdown of p202 expression in B6.Nba2 cells resulted in stimulation of p53-mediated transcription. We found that p202 bound to p53 in the N-terminal region (aa 44-83) comprising the proline-rich region that is important for p53-mediated apoptosis. Consistent with the binding of p202 to p53, increased expression of p202 in B6.Nba2 mouse embryonic fibroblasts inhibited UV-induced apoptosis. Taken together, our observations support the idea that increased expression of p202 in B6.Nba2 mice increases the susceptibility to develop lupus, in part, by inhibiting p53-mediated apoptosis.

Effects of MHC and gender on lupus-like autoimmunity in Nba2 congenic mice

The lupus-like disease that develops in hybrids of NZB and NZW mice is genetically complex, involving both MHC- and non-MHC-encoded genes. Studies in this model have indicated that the H2d/z MHC type, compared with H2d/d or H2z/z, is critical for disease development. C57BL/6 (B6) mice (H2b/b) congenic for NZB autoimmunity 2 (Nba2), a NZB-derived susceptibility locus on distal chromosome 1, produce autoantibodies to nuclear Ags, but do not develop kidney disease. Crossing B6.Nba2 to NZW results in H2b/z F1 offspring that develop severe lupus nephritis. Despite the importance of H2z in past studies, we found no enhancement of autoantibody production or nephritis in H2b/z vs H2b/b B6.Nba2 mice, and inheritance of H2z/z markedly suppressed autoantibody production. (B6.Nba2 x NZW)F1 mice, compared with MHC-matched B6.Nba2 mice, produced higher levels of IgG autoantibodies to chromatin, but not to dsDNA. Although progressive renal damage with proteinuria only occurred in F1 mice, kidneys of some B6.Nba2 mice showed similar extensive IgG and C3 deposition. We also studied male and female B6.Nba2 and F1 mice with different MHC combinations to determine whether increased susceptibility to lupus among females was also expressed within the context of the Nba2 locus. Regardless of MHC or the presence of NZW genes, females produced higher levels of antinuclear autoantibodies, and female F1 mice developed severe proteinuria with higher frequencies. Together, these studies help to clarify particular genetic and sex-specific influences on the pathogenesis of lupus nephritis.

New insights into disease pathogenesis from mouse lupus genetics

Full manifestation of mouse lupus, similar to the human disease in its severe form, is characterized by elevated antinuclear autoantibody levels and the development of kidney disease. Considerable evidence supports a genetic basis for lupus. The functional dissection of susceptibility loci in multigenic mouse models of lupus has provided insight into the immune abnormalities associated with autoantibody production and other processes critical for inflammation and damage in the kidney. The elucidation of models with single-gene manipulations has also identified immune mechanisms in the pathway to lupus. Recent advances have challenged previously accepted truths and new layers of complexity have become apparent.

Links between type I interferons and the genetic basis of disease in mouse lupus

Systemic lupus erythematosus (SLE), like other autoimmune diseases, is a complex genetic trait with contributions from both major histocompatibility complex (MHC) genes and multiple non-MHC genes. Most of the contributing genes have yet to be identified. Studies of mouse models of lupus have provided important insight into the immunopathogenesis of lupus-like IgG autoantibody production and lupus nephritis, and genetic analyses of these mice are helping to unravel the complex and heterogeneous genetic basis of disease. Recent studies in both human SLE and mouse models of lupus have emphasized a potential role of type I interferons (IFN-alpha/beta) in the initiation and perpetuation of disease. There is now increasing interest in genes that affect IFN-alpha/beta expression-activity and IFN-regulated target genes that may be involved in the disease process. One example is interferon-inducible gene 202 (Ifi202), which has been identified as a major candidate susceptibility gene in the New Zealand hybrid model of lupus. Studies suggest that increased expression of this transcription factor leads to lupus through inhibition of lymphocyte apoptosis, although its effects on immune function are extremely complex and have yet to be fully defined. This review will focus on the genetic basis of disease in mouse lupus with a special emphasis on those genetic contributions that may affect IFN-alpha/beta activity and those that may be target genes of IFN-alpha/beta action.

Interleukin-6 Induces Expression of Ifi202, an Interferon-inducible Candidate Gene for Lupus Susceptibility

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease. In human SLE patients, as well as in mouse models of SLE, the development of disease is associated with increased levels of pro-inflammatory cytokines, such as interleukin-6 (IL-6). However, IL-6 target genes contributing to the development of disease remain to be identified. Our previous studies of one mouse model of SLE identified an interferon-inducible gene, Ifi202, as a major contributor to the disease. We now report that IL-6 induces expression of the Ifi202 gene. We found that IL-6 treatment of mouse splenocytes increased levels of Ifi202 mRNA and p202 protein. Furthermore, IL-6 treatment of NIH 3T3 cells or expression of a constitutively active form of STAT3, a known mediator of IL-6 signaling, stimulated the activity of a 202-luc-reporter through a potential STAT3 DNA-binding site (the 202-SBS) present in the 5'-regulatory region of the Ifi202 gene. Moreover, treatment of cells with IL-6 stimulated binding of the transcription factor STAT3 to an oligonucleotide containing the 202-SBS in gel-mobility shift assays and to the 5'-regulatory region of the Ifi202 gene in chromatin immunoprecipitation assays. Importantly, site-directed mutagenesis of 202-SBS or expression of a dominant negative form of STAT3 significantly reduced constitutive as well as IL-6-stimulated activity of the 202-luc-reporter. Together, our observations support the idea that IL-6 stimulates transcription of the Ifi202 gene through STAT3 activation and predict that increased levels of IL-6 in lupus contribute to up-regulation of p202.

CD40 is Necessary for Activation of Naive T Cells by a Dendritic Cell Line In Vivo but not In Vitro

The importance of CD40-CD40L interactions during CD4(+) T-cell activation has been extensively investigated over the years; however, it still remains questionable whether the interaction is a prerequisite for dendritic cell (DC)-mediated antigen-specific priming in vivo. Naïve CD4(+) T cells require two signals for proper activation and induction of differentiation: signal 1 is provided by peptide antigens in the context of the major histocompatibility complex (MHC) class II, while signal 2 is delivered by costimulatory molecules such as CD80 or CD86 present on the antigen-presenting cell (APC). It is well known that the expression of CD80/CD86 is upregulated after interaction between CD40 on APCs and CD40L expressed by at least partly activated T cells. We used a DC line, JawsII, to compare the importance of CD40 expression and downstream signalling in vitro and in vivo. JawsII cells represent pre-immature bone marrow-derived DCs expressing low levels of MHC molecules, low levels of B7 molecules and no CD40. We have previously shown that JawsII cells, despite the lack of CD40 expression, are capable of priming naïve allogeneic T cells in vitro. In correlation with the current literature, we present data showing that constitutive expression of CD40 significantly increases the priming capacity of JawsII cells in vitro. In addition, we show that CD40 expression is required for JawsII cell-dependent T-cell priming in vivo.

Both exogenous and endogenous interleukin-10 affects the maturation of bone-marrow-derived dendritic cells in vitro and strongly influences T-cell priming in vivo

In order to avoid autoimmunity and excessive tissue destruction, the action of certain immunoinhibitory substances are very important for negative regulation of the immune system. Interleukin-10 (IL-10) is an important immunoregulatory cytokine which is thought to negatively affect both T cells and antigen-presenting cells in vivo. Adoptive transfer of IL-10-treated bone-marrow-derived dendritic cells (BMDCs) may be one therapeutic avenue to inhibit autoimmunity. In this study we present a comprehensive analysis of the effects of IL-10 on murine BMDC. We demonstrate that IL-10 can prevent BMDC maturation, as measured by both cytokine production and T-cell priming capacity in vitro. Furthermore, we show that IL-10 can inhibit DC maturation induced by strong stimulatory signals such as lipopolysaccharide or a mixture of cytokines (interferon-gamma, tumour necrosis factor-alpha, IL-4). Interestingly, maturation of both T helper 1- and T helper 2-inducing DCs, characterized by the induction of high levels of interferon-gamma and IL-4-production by responding T cells, respectively, was inhibited by IL-10 in vitro. Finally, our data suggest that both endogenous and exogenous IL-10 affect the T-cell stimulatory capacity of BMDCs after injection of in vitro-treated BMDCs into naïve mice. These data both support existing data as well as point towards a new understanding of the many aspects of IL-10-mediated immunosuppression.

Low expression of insulin in the thymus of non-obese diabetic mice

Insulin is a predominant autoantigen in IDDM in man and the NOD mouse. Failure of negative selection of diabetogenic T cells in thymus may be an important pre-disposing cause of the disease. To obtain insight into negative selection against such T-cell clones the thymic expression of insulin was studied in NOD and Balb/c mice by quantitative competitive RT-PCR. We detected RNA for insulin in the thymus of 3-week-old Balb/c mice as well as in NOD mice. However, the NOD mice expressed only half as many insulin transcripts as the Balb/c mice. Also, insulin protein was detected in the thymic medulla of both Balb/c and NOD mice. Furthermore, thymic RNA preparations were investigated for the presence of insulin transcription factors. None of the known pancreatic transcription factors for insulin; Pdx-1, Pax6 or Nkx6.1 were detectable in the thymus of Balb/c mice. These results support the idea that low insulin expression in the thymus may be a predisposing cause for development of diabetes in NOD mice analogous with what has been found in humans with the disease-disposing IDDM2 allele. Furthermore, our results suggest that insulin expression in the thymus may be regulated by different principles from those in the pancreas.

Treatment of an immortalized APC cell line with both cytokines and LPS ensures effective T-cell activation in vitro

Antigen-presenting cells (APCs) are crucial for the generation of a functional immune response to pathogens. Furthermore, there is abundant evidence for their importance in primary T-cell activation, B-cell maturation and maintenance of an ongoing immune response. In the present study, we have analysed phenotypic characteristics and functionality of a p53-deficient APC cell line (JawsII) derived from mouse bone marrow culture. We show that unstimulated JawsII cells express low surface levels of major histocompatibility complex (MHC) and costimulatory molecules, both of which can be upregulated upon treatment with cytokines in vitro. Cytokine stimulation also leads to an enhanced T-cell activation capacity but has only little effect on cytokine release by the JawsII cells themselves. On the contrary, stimulation of the JawsII cells with lipopolysaccharide (LPS) leads to the production and secretion of high amounts of interleukin-1 (IL-1), IL-6 and tumour necrosis factor-alpha (TNF-alpha) but no increase in the surface levels of MHC and costimulatory molecules, and has only little effect on the T-cell activation capacity. Our data suggest that the effects observed upon treatment with cytokines or LPSs are complementary, and that both stimuli are needed for mediating a strong and efficient JawsII cell-dependent T-cell activation.