A Toll for lupus

Lupus Nephritis: Current Perspectives and Moving Forward

Lupus nephritis is a severe organ manifestation of systemic lupus erythematosus, and its pathogenesis involves complex etiology and mechanisms. Despite significant knowledge gains and extensive efforts put into understanding the development and relapsing disease activity, lupus nephritis remains a substantial cause of morbidity and mortality in lupus patients. Current therapies retain a significant unmet medical need regarding rates of complete response, preventing relapse of lupus nephritis, progression of chronic kidney disease to kidney failure, drug toxicity, and pill burden-related drug non-adherence. Connected to progression of chronic kidney disease are the associated risks for disabling or even lethal cardiovascular events, as well as chronic kidney disease-related secondary immunodeficiency and serious infections. In this regard, biomarkers are needed that can predict treatment response to specific drugs to enable personalized precision medicine. A series of clinical trials with innovative immunomodulatory drugs are ongoing and raise expectations for improvements in the management of lupus nephritis. Here, we review how new developments in pathogenesis connect with current and future perspectives for the management of lupus nephritis.

Role of innate immune receptors TLR4 and TLR2 polymorphisms in systemic lupus erythematosus susceptibility

AIM

Through their recognition of various bacterial cell wall components, TLR2 and TLR4 participate in the innate response and modulate the activation of adaptive immunity. Therefore, the genetic background of these receptors might play a crucial role in autoimmune diseases such as systemic lupus erythematosus (SLE). In this study, we investigated the possible association between polymorphisms within TLR2 and TLR4 genes with SLE susceptibility.

MATERIAL AND METHODS

A total of 100 SLE patients and 200 unrelated healthy controls of the Tunisian population were enrolled in the study.TLR4rs4986790, TLR4rs4986791, and TLR2rs5743708 genotyping were performed using a polymerase chain reaction-restriction fragment length polymorphism method. The number of guanine-thymine (GT) repeat microsatellite in the intron 2 of TLR2 gene was analyzed by sequencing.

RESULTS

We reported a lack of allelic and genotypic association between SNPs of TLR4 and TLR2 genes and SLE pathogenesis. No correlation was found with any SLE features. However, SLE susceptibility was associated with the GT repeat microsatellite polymorphism in the human TLR2 gene. Further subclassification of alleles into three subclasses revealed a significant association between the long-sized repeats ((GT) >23) and SLE.

CONCLUSION

Though the results showed the absence of genetic association of TLR4 and TLR2 SNPs with the risk of developing SLE, we have identified a protective association between the microsatellite polymorphism in intron 2 of the TLR2 gene and SLE. Functionally, these (GT)n repeats may confer modifying effects or susceptibility to certain inflammatory conditions.

Type I interferons and endoplasmic reticulum stress in health and disease

Type I interferons (IFNs) comprise of pro-inflammatory cytokines created, as well as sensed, by all nucleated cells with the main objective of blocking pathogens-driven infections. Owing to this broad range of influence, type I IFNs also exhibit critical functions in many sterile inflammatory diseases and immunopathologies, especially those associated with endoplasmic reticulum (ER) stress-driven signaling pathways. Indeed, over the years accumulating evidence has indicated that the presence of ER stress can influence the production, or sensing of, type I IFNs induced by perturbations like pattern recognition receptor (PRR) agonists, infections (bacterial, viral or parasitic) or autoimmunity. In this article we discuss the link between type I IFNs and ER stress in various diseased contexts. We describe how ER stress regulates type I IFNs production or sensing, or how type I IFNs may induce ER stress, in various circumstances like microbial infections, autoimmunity, diabetes, cancer and other ER stress-related contexts.

The innate immune system in human systemic lupus erythematosus

Although the role of adaptive immune mechanisms, e.g. autoantibody formation and abnormal T-cell activation, has been long noted in the pathogenesis of human systemic lupus erythematosus (SLE), the role of innate immunity has been less well characterized. An intricate interplay between both innate and adaptive immune elements exists in protective anti-infective immunity as well as in detrimental autoimmunity. More recently, it has become clear that the innate immune system in this regard not only starts inflammation cascades in SLE leading to disease flares, but also continues to fuel adaptive immune responses throughout the course of the disease. This is why targeting the innate immune system offers an additional means of treating SLE. First trials assessing the efficacy of anti-type I interferon (IFN) therapy or modulators of pattern recognition receptor (PRR) signalling have been attempted. In this review, we summarize the available evidence on the role of several distinct innate immune elements, especially neutrophils and dendritic cells as well as the IFN system, as well as specific innate PRRs along with their signalling pathways. Finally, we highlight recent clinical trials in SLE addressing one or more of the aforementioned components of the innate immune system.

Nucleosome in patients with systemic sclerosis: possible association with immunological abnormalities via abnormal activation of T and B cells

OBJECTIVE

To determine the serum levels of nucleosome in patients with systemic sclerosis (SSc) and relate the results to the clinical features of SSc.

METHODS

Serum nucleosome levels in 91 patients with SSc were examined by ELISA. The expression of Toll-like receptor (TLR) 9 in T and B cells was quantified by flow cytometric intracellular protein analysis. The effects of nucleosomes on lymphocytes were also analysed. Moreover, we assessed the effects of nucleosomes on fibrosis, using wild type and CD19-deficient bleomycin-treated mice, an experimental model for human SSc.

RESULTS

Serum nucleosome levels were elevated in SSc compared with healthy controls and correlated positively with the extent of skin and pulmonary fibrosis and immunological abnormalities. The retrospective longitudinal analysis showed the serum nucleosome levels to be attenuated during the follow-up period. TLR9, which can be stimulated by nucleosome expression was upregulated in the affected T and B cells of patients with SSc. Moreover, nucleosome stimulation strongly increased interleukin (IL)-4 and IL-17 expression of T cells, B-cell IgG production and proliferation of lymphocytes in SSc compared with those in healthy controls. In bleomycin-induced SSc model mice, serum nucleosome levels were elevated compared with control mice. Furthermore, nucleosomes increased IgG production and proliferation of mouse B cells. Although TLR9 expression was similar between wild type and CD19-deficient splenic B cells, CD19 deficiency reduced these nucleosome effects.

CONCLUSION

These results suggest that nucleosomes and its signalling in B and T cells contribute to disease development in SSc via TLR9.

Systemic lupus erythematosus: epidemiology, pathophysiology, manifestations, and management

Systemic lupus erythematosus is a chronic autoimmune disorder characterized by production of autoantibodies directed against nuclear and cytoplasmic antigens, affecting several organs. Although cause is largely unknown, pathophysiology is attributed to several factors. Clinically, this disorder is characterized by periods of remission and relapse and may present with various constitutional and organ-specific symptoms. Diagnosis is achieved via clinical findings and laboratory examinations. Therapies are based on disease activity and severity. General treatment considerations include sun protection, diet and nutrition, smoking cessation, exercise, and appropriate immunization, whereas organ-specific treatments include use of steroidal and nonsteroidal anti-inflammatory drugs, immunosuppressive agents, and biologic agents.

Acceleration of SLE-like syndrome development in NZBxNZW F1 mice by beta-glucan

Beta-glucans are naturally occurring polysaccharides that exert important immunostimulatory activities. In the present study, we evaluated whether beta-glucans could modulate the development and the course of systemic lupus erythematosus (SLE). To this aim, we employed the classical model of SLE represented by the F1 hybrid between the NZB and NZW mouse strains which develop severe lupus-like phenotypes comparable to that of SLE patients. The administration of beta-glucan was associated to a more aggressive development of the disease and a worse prognosis, as observed from the clinical, biochemical and histopathological data. This finding implies that restraint should be practised in the possible use of beta-glucans as immunomodulators in human therapy in the context of SLE.

Toll-like receptor and accessory molecule mRNA expression in humans and mice as well as in murine autoimmunity, transient inflammation, and progressive fibrosis

The cell type-, organ-, and species-specific expression of the Toll-like receptors (TLRs) are well described, but little is known about the respective expression profiles of their accessory molecules. We therefore determined the mRNA expression levels of LBP, MD2, CD36, CD14, granulin, HMGB1, LL37, GRP94, UNC93b1, TRIL, PRAT4A, AP3B1, AEP and the respective TLRs in human and mouse solid organs. Humans and mice displayed significant differences between their respective mRNA expression patterns of these factors. In addition, the expression profiles in transient tissue inflammation upon renal ischemia-reperfusion injury, in spleens and kidneys from mice with lupus-like systemic autoimmunity, and in progressive tissue fibrosis upon unilateral ureteral obstruction were studied. Several TLR co-factors were specifically regulated during the different phases of these disease entities, suggesting a functional involvement in the disease process. Thus, the organ- and species-specific expression patterns need to be considered in the design and interpretation of studies related to TLR-mediated innate immunity, which seems to be involved in the tissue injury phase, in the phase of tissue regeneration, and in progressive tissue remodelling.

Toll-like receptors in systemic lupus erythematosus: potential targets for therapeutic intervention

Toll-like receptors (TLRs) have attracted increased attention in recent years, not only for their role in sensing conserved microbial components, but also in the realm of autoimmunity. Although TLRs are most widely known for their capacity to detect conserved motifs of infectious agents, mounting evidence indicates that these innate receptors also promote autoimmune conditions by causing uncontrolled autoinflammation as a result of chronic recognition of self. In response to the need for modern approaches to treatment of autoimmune diseases, several groups have begun investigating ways to target TLRs as new therapeutic options for autoimmune conditions. Here we discuss recent data describing advances in TLRs as therapeutic targets for treatment of autoimmune diseases, with a focus on systemic lupus erythematosus.

The pathogenesis of systemic lupus erythematosus-an update

Systemic lupus erythematosus (SLE, lupus) is characterized by a global loss of self-tolerance with activation of autoreactive T and B cells leading to production of pathogenic autoantibodies and tissue injury. Innate immune mechanisms are necessary for the aberrant adaptive immune responses in SLE. Recent advances in basic and clinical biology have shed new light on disease mechanisms in lupus, with this review discussing the recent studies that offer valuable insights into disease-specific therapeutic targets.

17β-Estradiol enhances response of mice spleen B cells elicited by TLR9 agonist

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies against nucleic acid-associated antigens. B cells play cardinal roles in SLE. Many evidences have proved estrogen contribute to the gender bias in SLE and 17β-estradiol (E2) could accelerate the disease by regulating B cells. On the other hand, B cells express TLR9 which recognized dsDNA and played a critical role in SLE. However, the crosstalk between estrogen and TLR9 in B cells remains unknown. So we investigated the E2 effect in the presence of the TLR9 ligand CpG on mice spleen B cells. We found that the up-regulation of cell viability, life-span, co-stimulation molecules (CD40, CD86) expression, IgM secretion, TLR9 and MCM6 expression were more significant than CpG ODN or E2 stimulated alone. It may provide a new way to investigate the mechanism of how E2 modulate the B cells function in lupus.

Fibronectin inhibits cytokine production induced by CpG DNA in macrophages without direct binding to DNA

Fibronectin (FN) is known to have four DNA-binding domains although their physiological significance is unknown. Primary murine peritoneal macrophages have been shown to exhibit markedly lower responsiveness to CpG motif-replete plasmid DNA (pDNA), Toll-like receptor-9 (TLR9) ligand, compared with murine macrophage-like cell lines. The present study was conducted to examine whether FN having DNA-binding domains is involved in this phenomenon. The expression of FN was significantly higher in primary macrophages than in a macrophage-like cell line, RAW264.7, suggesting that abundant FN might suppress the responsiveness in the primary macrophages. However, electrophoretic analysis revealed that FN did not bind to pDNA in the presence of a physiological concentration of divalent cations. Surprisingly, marked tumor necrosis factor - (TNF-)α production from murine macrophages upon CpG DNA stimulation was significantly reduced by exogenously added FN in a concentration-dependent manner but not by BSA, laminin or collagen. FN did not affect apparent pDNA uptake by the cells. Moreover, FN reduced TNF-α production induced by polyI:C (TLR3 ligand), and imiquimod (TLR7 ligand), but not by LPS (TLR4 ligand), or a non-CpG pDNA/cationic liposome complex. The confocal microscopic study showed that pDNA was co-localized with FN in the same intracellular compartment in RAW264.7, suggesting that FN inhibits cytokine signal transduction in the endosomal/lysosomal compartment. Taken together, the results of the present study has revealed, for the first time, a novel effect of FN whereby the glycoprotein modulates cytokine signal transduction via CpG-DNA/TLR9 interaction in macrophages without direct binding to DNA through its putative DNA-binding domains.

5'-Phosphate oligodeoxynucleotides enhance the phosphodiester-CpG DNA-induced inflammatory response in macrophages

Dying cells release genomic DNA into the surroundings where the DNA is first degraded to oligodeoxynucleotides, then to nucleotides, nucleosides and so on. Given that the unmethylated CpG dinucleotide (CpG motif), which is characteristic of bacterial DNA, is also contained in mammalian DNA and has been reported to be involved in the exacerbation of DNA-associated autoimmune diseases, we investigated whether nucleotides and nucleosides affect immune responses to phosphodiester (PO)-CpG DNA. Addition of non-CpG DNA to RAW264.7, murine macrophage-like cells, induced no significant TNF-α production irrespective of treatment with DNase I; however, DNase I-treated, but not untreated, non-CpG DNA increased the PO-CpG DNA-mediated TNF-α production. This increase was not observed with phosphorothioate-CpG DNA or ligands for TLR3, TLR4 or TLR7. Deoxynucleotides with a 5'-phosphate showed similar effects to those of DNase I-treated non-CpG DNA, but DNase II-treated DNA or deoxynucleosides did not. Subcutaneous injection of PO-CpG DNA into the mouse footpad induced little swelling of the paw; however, significant swelling was observed when DNase I-treated DNA was co-injected with PO-CpG DNA. These results imply that PO-CpG DNA-dependent inflammatory responses are increased by DNA molecules with a 5'-phosphate; such molecules could therefore be considered as exacerbating factors for CpG motif-related inflammation.

Targeting Toll-like receptors for treatment of SLE

Toll-like receptors (TLRs) are important innate immune receptors for the identification and clearance of invading pathogens. Twelve TLRs that recognize various conserved components of microorganisms are currently known. Among these, the endosomal TLRs 3, 7/8, and 9 recognize dsRNA, ssRNA, and CpG DNA, respectively. Nucleic acid-sensing TLRs, TLR 7 in particular, have been implicated in systemic lupus erythematosus (SLE) and are thought to exacerbate disease pathology. Activation of these TLRs results in the production of inflammatory cytokines and type I interferon. Genome-wide association studies, single nucleotide polymorphism analyses as well as experimental mouse models have provided evidence of TLR signaling involvement in SLE and other autoimmune diseases. Since activation of these receptor pathways promotes autoimmune phenotypes, inhibitory drugs that target these pathways constitute important new therapeutic strategies for the treatment of systemic autoimmunity.

Expression of Toll-like receptor 9 in renal podocytes in childhood-onset active and inactive lupus nephritis

BACKGROUND

Childhood-onset systemic lupus erythematosus (SLE) is frequently complicated with lupus nephritis (LN), which is characterized by the deposition of DNA-containing immune complex to the glomerulus. Toll-like receptor 9 (TLR9), capable of recognizing the microbially derived CpG oligonucleotide, plays a crucial role in the innate immunity. TLR9 is also assumed to be related to the aetiology of SLE in the recognition of anti-DNA antibody-containing immune complex, but this remains controversial. We conducted a study to elucidate the association between TLR9 and LN in childhood-onset SLE.

METHODS

We compared the expression and localization of TLR9 and the slit membrane-related protein in the biopsied kidney sample by immunostaining in four children with active or inactive LN. We also evaluated their laboratory findings, such as anti-DNA antibody, complement and proteinuria at biopsy, to assess the correlation to the findings of the immunostaining.

RESULTS

TLR9 is not expressed in a normal control kidney. However, TLR9 develops in podocytes only in active LN but disappears in remission. Meanwhile, the slit membrane-related proteins such as nephrin, podocin and synaptopodin in podocytes express clearly and uniformly in remission, but their expression is markedly diminished in active LN, which results in podocyte injury. When TLR9 is expressed in podocytes, all the patients simultaneously showed hypocomplementaemia, high titre of anti-double-stranded DNA (dsDNA) antibody and proteinuria.

CONCLUSION

Injured podocytes in active LN express TLR9. This expression could be associated with proteinuria and increased anti-dsDNA antibody. This is the first report indicating that TLR9 is involved in the aetiology of LN and that it may play some role in podocyte injury.

Up-regulation of the endoplasmic reticulum transmembrane protein UNC93B in the B cells of patients with active systemic lupus erythematosus

OBJECTIVES

The transmembrane endoplasmic reticulum (ER) protein UNC93B plays an essential role in the normal response to signalling through intracellular Toll-like receptor (TLR)3, TLR7, TLR8 and TLR9. In the current study, we examined the level of UNC93B expression on peripheral B cells from patients with active SLE, and investigated any correlation with SLE pathogenesis.

METHODS

Peripheral blood mononuclear cells (PBMCs) and B cells from 43 active SLE patients were analysed by quantitative RT-PCR to determine the precise levels of UNC93B mRNA. We also analysed UNC93B protein expression on B cells from SLE patients using immunoblotting.

RESULTS

The expression of UNC93B mRNA on PBMCs from active SLE patients was significantly higher than that of controls (P < 0.05). The intracellular expression level of UNC93B protein on CD20(+) B cells from active SLE patients was also higher than in the controls. Moreover, the expression of UNC93B on B cells from lupus patients correlated significantly with high titres of anti-dsDNA antibody (P < 0.05).

CONCLUSIONS

Up-regulation of the ER membrane protein UNC93B on human lupus B cells suggests that TLR9 and UNC93B play a partial role in the pathogenesis of SLE by inducing defective peripheral B-cell tolerance.

Type I interferons produced by resident renal cells may promote end-organ disease in autoantibody-mediated glomerulonephritis

Increased Type I IFNs or IFN-I have been associated with human systemic lupus erythematosus. Interestingly augmenting or negating IFN-I activity in murine lupus not only modulates systemic autoimmunity, but also impacts lupus nephritis, suggesting that IFN-I may be acting at the level of the end-organ. We find resident renal cells to be a dominant source of IFN-I in an experimental model of autoantibody-induced nephritis. In this model, augmenting IFN-I amplified antibody-triggered nephritis, whereas ablating IFN-I activity ameliorated disease. One mechanism through which increased IFN-I drives immune-mediated nephritis might be operative through increased recruitment of inflammatory monocytes and neutrophils, though this hypothesis needs further validation. Collectively, these studies indicate that an important contribution of IFN-I toward the disease pathology seen in systemic autoimmunity may be exercised at the level of the end-organ.

Regulation of dendritic cells by female sex steroids: Relevance to immunity and autoimmunity

Dendritic cells (DCs) are critical mediators of adaptive immunity, tolerance and autoimmunity. The human immune system exhibits sexual dimorphism, which is most evident in the female predominance of autoimmune diseases such as systemic lupus erythematosus (SLE). Female sex steroids are strongly implicated in mediating immune sexual dimorphism, in part because estrogen accentuates disease in several models of lupus autoimmunity. In contrast, progesterone may prevent disease development. While much investigation has focused on the effects of estrogen and progesterone on lymphocyte functions, far less attention has been paid to the effects of these hormones on DCs. Current evidence now indicates estrogen can activate DCs, while in contrast, progesterone inhibits DC functions. Thus, we hypothesize that the opposite effects these two hormones have on lupus autoimmunity reflect opposing effects on DC functions. Thus, through direct actions on DCs, female sex steroids may influence autoimmunity, immunity and tolerance.

Association study of a single nucleotide polymorphism in the exon 2 region of toll-like receptor 9 (TLR9) gene with susceptibility to systemic lupus erythematosus among Chinese

Toll-like receptor 9 (TLR9) plays an important role in the induction and regulation of the innate immune system or adaptive immune responses. Genetic variations within human TLR9 have been reported to be associated with a range of immune-related diseases, such as asthma, systemic lupus erythematosus (SLE) and so on. Family-based association analysis was performed to further investigate whether a single nucleotide polymorphism (rs352140) in the exon 2 region of TLR9 gene is associated with susceptibility to SLE in a Chinese population. A total of 77 patients with SLE from 74 nuclear families, aged from 12 to 63 years, were enrolled according to 1997 criteria of American College of Rheumatology (ACR), 211 family members of these patients were also included. Genotyping was performed by PCR-restriction fragment length polymorphism (PCR-RFLP) assay. Among 77 patients with SLE, the CC, CT and TT genetype frequencies of the SNP (rs352140) were 20.8, 61.0 and 18.2%, respectively. Single loci analysis suggested that the T allele at position of rs352140 was significantly associated with the susceptibility to SLE (Z = 2.357, P = 0.018402) in dominant model, but not in additive or recessive model. Genetype analysis showed that individuals with CT genetype had greater susceptibility to SLE than those without (Z = 2.004, P = 0.045067). Our study suggests that a single nucleotide polymorphism (rs352140) in the exon 2 region of TLR9 gene may be a susceptibility factor for SLE in Chinese population.

Epigenetic regulation and the pathogenesis of systemic lupus erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is incompletely understood. Studies in both lupus animal models and human disease indicate a clear role for epigenetic defects, particularly DNA methylation, in the pathogenesis of lupus. T-cell DNA from active lupus patients is hypomethylated, which results in overexpression of methylation-regulated genes, T-cell autoreactivity, and autoimmunity in vivo. Inducing an extracellular signal-regulated kinase (ERK) signaling defect in T cells using a transgenic mouse model resulted in reduced DNA methyltransferase 1 (DNMT1) expression, overexpression of methylation-sensitive genes, and anti-double-stranded DNA (anti-dsDNA) antibody production. ERK signaling is known to be defective in lupus T cells, and this defect is now explained by impaired T-cell protein kinase C (PKC) delta activation. Herein, we discuss how defective epigenetic regulation is involved in the pathogenesis of lupus, which includes both DNA methylation and histone modification changes.

[CCL2/MCP1: a novel target in systemic lupus erythematosus and lupus nephritis]

Cytokine blockade, a valid therapeutic concept, is not established in lupus nephritis as yet. In lupus nephritis CCL2/MCP-1 and its chemokine receptor CCR2 are of interest because CCL2/CCR2 mediate the recruitment of macrophages and T cells in the nephritic kidney. Lupus nephritis is markedly attenuated in CCL2- or CCR2-deficient autoimmune mice. Epidemiological studies addressing mutations in the CCL2 gene support the hypothesis that CCL2 mediates renal inflammation. Meanwhile experimental studies have shown that several classes of CCL2 antagonists can control established lupus nephritis. Interestingly, therapeutic CCL2 blockade does not affect the autoimmune lymphoproliferative syndrome and the production of lupus autoantibodies. This article briefly summarizes the potential role of therapeutic CCL2 blockade in lupus nephritis.

Systemic IFN-alpha drives kidney nephritis in B6.Sle123 mice

The impact of IFN-alpha secretion on disease progression was assessed by comparing phenotypic changes in the lupus-prone B6.Sle1Sle2Sle3 (B6.Sle123) strain and the parental C57BL/6 (B6) congenic partner using an adenovirus (ADV) expression vector containing a recombinant IFN-alpha gene cassette (IFN-ADV). A comprehensive comparison of cell lineage composition and activation in young B6 and B6.Sle123 mice revealed a variety of cellular alterations in the presence and absence of systemic IFN-alpha. Most IFN-alpha-induced phenotypes were similar in B6 and B6.Sle123 mice; however, B6.Sle123 mice uniquely exhibited increased B1 and plasma cells after IFN-alpha exposure, although both strains had an overall loss of mature B cells in the bone marrow, spleen and periphery. Although most of the cellular effects of IFN-alpha were identical in both strains, severe glomerulonephritis occurred only in B6.Sle123 mice. Mice injected with IFN-ADV showed an increase in immune complex deposition in the kidney, together with an unexpected decrease in serum anti-nuclear antibody levels. In summary, the predominant impact of systemic IFN-alpha in this murine model is an exacerbation of mechanisms mediating end organ damage.

Yaa autoimmune phenotypes are conferred by overexpression of TLR7

The Y-linked autoimmune accelerating (Yaa) locus drives the transition to fatal lupus nephritis when combined with B6.Sle1 in our C57BL/6J (B6)-congenic model of systemic autoimmunity. We and others recently demonstrated that the translocation of a cluster of X-linked genes onto the Y chromosome is the genetic lesion underlying Yaa (Subramanian, S. et al., Proc. Natl. Acad. Sci. USA 2006. 103: 9970-9975; Pisitkun, P. et al., Science 2006. 312: 1669-1672). In male mice carrying Yaa, the transcription of several genes within the translocated segment is increased roughly twofold. Although the translocated X chromosome segment in Yaa may contain as many as 16 genes, the major candidate gene for causation of the Yaa-associated autoimmune phenotypes has been TLR7. To confirm the role of TLR7 in Yaa-mediated autoimmune phenotypes, we introgressed a targeted disruption of TLR7 (TLR7(-)) onto B6.Sle1Yaa to produce B6.Sle1YaaTLR7(-) and examined evidence of disease at 6 and 9 months of age. Our results demonstrate that the up-regulation of TLR7 in the B6.Sle1Yaa strain is responsible for splenomegaly, glomerular nephritis and the majority of the cellular abnormalities of B, T and myeloid cells. The up-regulation of TLR7 was also responsible for driving the infiltration and activation of leukocytes in the kidney, in which activated T cells were a primary component. However, the resolution of TLR7 up-regulation did not eliminate the enhanced humoral autoimmunity observed in B6.SleYaa, suggesting that additional elements in the translocation may contribute to the disease phenotype.

Cutting edge: progesterone regulates IFN-alpha production by plasmacytoid dendritic cells

Use of the progesterone (Pg) birth control depot medroxyprogesterone acetate (DMPA) increases a woman's risk for sexually transmitted infection with HIV or HSV-2 via unknown mechanisms. Plasmacytoid dendritic cells (pDCs) are circulating and tissue-resident sentinels capable of making large quantities of IFN-alpha upon recognizing viruses through TLRs 7 and 9. In this study, we show that Pg inhibits TLR9-induced IFN-alpha production by human and mouse pDCs and that DMPA impairs TLR9- and virus-induced IFN-alpha production by pDCs in mice, providing a potential explanation for how DMPA impairs innate antiviral immunity in women. Pg failed to inhibit the Mda-5 pathway of IFN-alpha induction in dendritic cells, suggesting that Pg regulates select antiviral DC programs. This may occur through selective blockade of IFN regulatory factor-7 activation, a novel steroid action. Thus, through inhibition of TLR-mediated IFN-alpha production by pDCs, Pg may regulate antiviral immunity.

Primer: signal transduction in rheumatic disease--a clinician's guide

Signaling pathways enable cells to respond and adapt to environmental stimuli. For instance, extracellular ligands, such as proinflammatory cytokines or pathogen components, bind receptors on the surface of cells that trigger downstream signaling cascades driven by enzymes called kinases. Ultimately, kinases activate transcription factors that bind to DNA and alter the expression of target genes, the products of which allow the cell to respond to the initial stimulus. A variety of chronic inflammatory diseases are associated with altered cellular signaling. Some of the signal cascades that are involved in inflammation and autoimmunity include those mediated by mitogen-activated protein kinases, nuclear factor-kappaB, interferon regulatory factor and Toll-like receptors, NOD-like receptors and the inflammasome, and phosphatidylinositol-3-kinases. Understanding these intracellular pathways might lead to new approaches to the treatment of inflammatory disease, including the use of orally bioavailable small molecules that regulate cytokine function and production.

Genetic variations of Toll-like receptor 9 predispose to systemic lupus erythematosus in Japanese population

BACKGROUND

Systemic lupus erythematosus (SLE) is characterised by dysregulation of autoreactive lymphocytes and antigen-presenting cells. Signalling through Toll-like receptor 9 (TLR9), a mediator of innate immune responses, has a role in activation of dendritic cells and autoreactive B cells.

OBJECTIVE

To investigate whether TLR9 polymorphisms are associated with an increased risk of SLE.

METHODS

DNA samples were obtained from 220 Japanese patients with SLE (with >4 American College of Rheumatology criteria for SLE) and 203 controls. The genetic variations of TLR9 were detected by PCR, followed by DNA sequencing. The promoter and enhancer activities of TLR9 were measured by luciferase reporter gene assay. The titres of anti-dsDNA antibodies in sera from control or TLR9-deficient mice were analysed by ELISA.

RESULTS

The G allele at position +1174 (located in intron 1 of TLR9) is closely associated with an increased risk of SLE (p = 0.029). Furthermore, patients with SLE tend to have C allele at position -1486 (p = 0.11). Both alleles down regulate TLR9 expression by reporter gene assay. TLR9-deficient mice under a C57BL/6 background possess higher titres of anti-dsDNA serum antibodies than control C57BL/6 mice.

CONCLUSIONS

These results indicate that the presence of the G allele at position +1174 of TLR9 predisposes humans to an increased risk of SLE. It is speculated that TLR9 normally prevents the development of human SLE.

Vaccine adjuvants revisited

The development of new adjuvants for human vaccines has become an expanding field of research in the last thirty years, for generating stronger vaccines capable of inducing protective and long-lasting immunity in humans. Instead of such efforts, with several adjuvant strategies approaching to requirements for their clinical application, limitations like adjuvant toxicity remain to be fully surpassed. Here we summarize the current status of adjuvant development, including regulatory recommendations, adjuvant requirements, and adjuvant categories like mineral salts, tensoactive compounds, microorganism-derived adjuvants, emulsions, cytokines, polysaccharides, nucleic acid-based adjuvants, and a section dedicated to particulate antigen delivery systems. The mechanisms of adjuvanticity are also discussed in the light of recent findings on Toll-like receptors' biology and their involvement on immune activation.

RNA interference and innate immunity

RNA interference is an evolutionarily conserved gene silencing process triggered by double-stranded RNAs. Common to all cell types, is the production of 21-24 nucleotide small interfering RNA (siRNAs), which guide the RNA-induced silencing complex (RISC) to identify and cleave target mRNA sequences. Presently, this biological breakthrough method has revolutionised gene function studies and holds great promise as validating drug targets and treating human diseases. However, despite the success that has been achieved by this technology, studies carried in human blood cells have revealed that siRNAs could generate bystander effects, including the activation of innate immunity and inhibition of unintended target genes. Interestingly, 2' uridine-modified siRNAs did not trigger TLR signalling, but they totally suppressed immune activation by immunostimulatory siRNAs when both molecules where delivered to the same endosomes. This review describes the recent advances in understanding the innate immune response to both single and double-stranded siRNAs. Also, it highlights the spectrum of molecular strategies allowing the design of therapeutic siRNAs with minimal side effects.

Nucleic acid-sensing TLRs as modifiers of autoimmunity

The immune system requires precise regulation of activating and inhibitory signals so that it can mount effective responses against pathogens while ensuring tolerance to self-components. Some of the most potent activation signals are triggered by innate immune molecules, particularly those in the TLR family. Recent studies have shown that engagement of TLRs plays a significant role in both innate and adaptive immunity. This review focuses on the ways that TLR function might contribute to the etiology of lupus-like syndromes in the context of an autoimmune-prone environment. By considering the sources, localization, and expression of both nucleic acids and the molecules that bind them, we discuss several ways that innate immunity can play a role in the development of systemic autoimmunity.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

Role of TLR9 in anti-nucleosome and anti-DNA antibody production in lpr mutation-induced murine lupus

Systemic lupus erythematosus is characterized by the production of autoantibodies directed against nuclear Ags, including nucleosome and DNA. TLR9 is thought to play a role in the production of these autoantibodies through the capacity of nuclear immunogenic particles to interact both with BCR and TLR9. To determine the role of TLR9 in SLE, C57BL/6-lpr/lpr-TLR9(-/-) and TLR9(+/+) mice were analyzed. The abrogation of TLR9 totally impaired the production of anti-nucleosome Abs, whereas no difference was observed in the frequency of anti-dsDNA autoantibodies whose titer was strikingly higher in TLR9(-/-) mice. In addition a higher rate of mesangial proliferation was observed in the kidney of TLR9-deficient animals. These results indicate that in C57BL/6-lpr/lpr mice, TLR9 is absolutely required for the anti-nucleosome Ab response but not for anti-dsDNA Ab production which is involved in mesangial proliferation.

Autoimmunity in systemic lupus erythematosus: integrating genes and biology

Susceptibility to the autoimmune phenotype of systemic lupus erythematosus (SLE) is heritable. Linkage analysis and recent advances in the field of single nucleotide polymorphisms (SNPs) have resulted in the identification of several genetic loci and functional allelic variants of signaling proteins which have become the mainstay of understanding disease susceptibility and exploring the basis of autoimmunity in SLE. However, genetic heterogeneity and possible epistatic interactions among genetic elements have precluded replication of these findings in multiple population groups and thus complicated their interpretation. In this regard, the discovery that a plethora of normal signaling proteins are expressed in abnormal amounts in immune cells from patients with SLE has gained significance. Thus, the key to precise elucidation of the pathologic basis of autoimmunity in SLE lies in tying genetics and disease biology. This review highlights recent discoveries of important functional genetic variants and altered expression of normal signaling proteins that network together to disrupt peripheral tolerance and initiate the autoimmune process in SLE.

Targeting Toll-like receptor signaling in plasmacytoid dendritic cells and autoreactive B cells as a therapy for lupus

This review focuses on the role of Toll-like receptors (TLRs) in lupus and on possibilities to treat lupus using TLR modulating inhibitory oligodeoxynucleotides (INH-ODNs). TLRs bridge innate and adaptive immune responses and may play an important role in the pathogenesis of systemic lupus erythematosus. Of particular interest are TLR3, -7, -8, and -9, which are localized intracellularly. These TLRs recognize single-stranded or double-stranded RNA or hypomethylated CpG-DNA. Exposure to higher order CpG-DNA ligands or to immune complexed self-RNA triggers activation of autoreactive B cells and plasmacytoid dendritic cells. INH-ODNs were recently developed that block all downstream signaling events in TLR9-responsive cells. Some of these INH-ODNs can also target TLR7 signaling pathways. Based on their preferential cell reactivity, we classify INH-ODNs into class B and class R. Class B ('broadly reactive') INH-ODNs target a broad range of TLR-expressing cells. Class R ('restricted') INH-ODNs easily form DNA duplexes or higher order structures, and are preferentially recognized by autoreactive B cells and plasmacytoid dendritic cells, rather than by non-DNA specific follicular B cells. Both classes of INH-ODNs can block animal lupus. Hence, therapeutic application of these novel INH-ODNs in human lupus, particularly class R INH-ODNs, may result in more selective and disease-specific immunosuppression.

Toll-like receptor-7 modulates immune complex glomerulonephritis

Viral infections may trigger immune complex glomerulonephritis via Toll-like receptors (TLR), as certain TLR trigger immunity upon recognition of viral nucleic acids. On the basis of previous findings regarding viral double-stranded RNA and TLR3 in experimental lupus erythematosus, a similar role for TLR7 that recognizes viral single-stranded RNA was hypothesized. Immunostaining of kidney sections of nephritic MRLlpr/lpr mice revealed TLR7 expression in infiltrating ER-HR3-positive macrophages and few CD11c-positive dendritic cells but not in glomerular mesangial cells as observed for TLR3. This finding was consistent with the distribution pattern of intravenously injected single-stranded RNA in nephritic MRLlpr/lpr mice. TLR7 ligation activated monocytes and dendritic cells, both isolated from MRLlpr/lpr mice, to secrete IFN-alpha, IL-12p70, IL-6, and CCL2. In vivo, a single injection of the TLR7 ligand imiquimod increased serum levels of IL-12p70, IFN-alpha, and IL-6. A course of 25 microg of imiquimod given every other day from week 16 to 18 of age aggravated lupus nephritis in MRLlpr/lpr mice. This was associated with increased glomerular immune complex deposits as well as interstitial expression of CCL2 in imiquimod-treated MRLlpr/lpr mice. Different types of viral nucleic acids seem to modulate systemic autoimmunity through specific interactions with their respective TLR. Different TLR expression profiles on immune cell subsets and nonimmune parenchymal cell types determine the molecular mechanisms involved in viral infection-associated exacerbation of lupus nephritis and possibly other types of immune complex glomerulonephritis.