The role of toll-like receptors in systemic lupus erythematosus

Human and Murine Toll-like Receptor-Driven Disease in Systemic Lupus Erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is linked to the differential roles of toll-like receptors (TLRs), particularly TLR7, TLR8, and TLR9. TLR7 overexpression or gene duplication, as seen with the Y-linked autoimmune accelerator (Yaa) locus or TLR7 agonist imiquimod, correlates with increased SLE severity, and specific TLR7 polymorphisms and gain-of-function variants are associated with enhanced SLE susceptibility and severity. In addition, the X-chromosome location of TLR7 and its escape from X-chromosome inactivation provide a genetic basis for female predominance in SLE. The absence of TLR8 and TLR9 have been shown to exacerbate the detrimental effects of TLR7, leading to upregulated TLR7 activity and increased disease severity in mouse models of SLE. The regulatory functions of TLR8 and TLR9 have been proposed to involve competition for the endosomal trafficking chaperone UNC93B1. However, recent evidence implies more direct, regulatory functions of TLR9 on TLR7 activity. The association between age-associated B cells (ABCs) and autoantibody production positions these cells as potential targets for treatment in SLE, but the lack of specific markers necessitates further research for precise therapeutic intervention. Therapeutically, targeting TLRs is a promising strategy for SLE treatment, with drugs like hydroxychloroquine already in clinical use.

Identification of a novel mutation in complement receptor 2 in Chinese familial systemic lupus erythematosus

Objectives

This study aims to analyze the relationship between complement receptor 2 (CR2) gene mutation and the clinical phenotype in Chinese familial systemic lupus erythematosus (SLE).

Patients and methods

A total of one Chinese familial SLE patients (median age: 30.25 years; range, 22 to 49 years) were included between January 2017 and December 2018. The clinical features and diagnoses of familial SLE patients were analyzed using whole-exome sequencing (WES) of genomic deoxyribonucleic acid (DNA) samples. Sanger sequencing was used to verify candidate mutations detected in the examined family.

Results

The mother and her three daughters were diagnosed with SLE. The clinical characteristics showed that the patient and her mother were diagnosed with lupus nephritis. The eldest daughter had decreased renal function and lower serum albumin levels. Immunological index analysis showed that all four patients were positive for anti-SSA and antinuclear antibody (ANA), but that only the second daughter was positive for anti-double-stranded DNA (dsDNA). Complement 3 (C3) was significantly decreased in all patients, while evaluation of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) showed that the second and third daughters had mild active SLE. The mother and eldest daughter were treated with prednisolone combined with cyclophosphamide, while the other two daughters were treated with prednisolone alone. The WES and Sanger sequencing analyses revealed an unreported missense T>C mutation c.2804 in the 15^th exon of the CR gene in all four patients.

Conclusion

We identified a novel c.2804 (exon 15) T>C mutation in the CR gene of Chinese familial SLE. This mutation was previously reported, suggesting that the CR gene c.2804 (exon 15) T>C mutation is the probable cause of SLE in this family.

Targeting DAMPs with nucleic acid scavengers to treat lupus

Systemic lupus erythematosus (SLE) is a chronic and often progressive autoimmune disorder marked clinically by a variable constellation of symptoms including fatigue, rash, joint pains, and kidney damage. The lungs, heart, gastrointestinal system, and brain can also be impacted, and individuals with lupus are at higher risk for atherosclerosis, thrombosis, thyroid disease, and other disorders associated with chronic inflammation . Autoimmune diseases are marked by erroneous immune responses in which the target of the immune response is a "self"-antigen, or autoantigen, driven by the development of antigen-specific B or T cells that have overcome the normal systems of self-tolerance built into the development of B and T cells. SLE is specifically characterized by the production of autoantibodies against nucleic acids and their binding proteins, including anti-double stranded DNA, anti-Smith (an RNA binding protein), and many others . These antibodies bind their nuclear-derived antigens to form immune complexes that cause injury and scarring through direct deposition in tissues and activation of innate immune cells . In over 50% of SLE patients, immune complex aggregation in the kidneys drives intrarenal inflammation and injury and leads to lupus nephritis, a progressive destruction of the glomeruli that is one of the most common causes of lupus-related death . To counter this pathology increasing attention has turned to developing approaches to reduce the development and continued generation of such autoantibodies. In particular, the molecular and cellular events that lead to long term, continuous activation of such autoimmune responses have become the focus of new therapeutic strategies to limit renal and other pathologies in lupus patients. The focus of this review is to consider how the innate immune system is involved in the development and progression of lupus nephritis and how a novel approach to inhibit innate immune activation by neutralizing the activators of this response, called Damage Associated Molecular Patterns, may represent a promising approach to treat this and other autoimmune disorders.

Altered Germinal-Center Metabolism in B Cells in Autoimmunity

B lymphocytes play an important role in the pathophysiology of many autoimmune disorders by producing autoantibodies, secreting cytokines, and presenting antigens. B cells undergo extreme physiological changes as they develop and differentiate. Aberrant function in tolerogenic checkpoints and the metabolic state of B cells might be the contributing factors to the dysfunctionality of autoimmune B cells. Understanding B-cell metabolism in autoimmunity is important as it can give rise to new treatments. Recent investigations have revealed that alterations in metabolism occur in the activation of B cells. Several reports have suggested that germinal center (GC) B cells of individuals with systemic lupus erythematosus (SLE) have altered metabolic function. GCs are unique microenvironments in which the delicate and complex process of B-cell affinity maturation occurs through somatic hypermutation (SHM) and class switching recombination (CSR) and where Bcl6 tightly regulates B-cell differentiation into memory B-cells or plasma cells. GC B cells rely heavily on glucose, fatty acids, and oxidative phosphorylation (OXPHOS) for their energy requirements. However, the complicated association between GC B cells and their metabolism is still not clearly understood. Here, we review several studies of B-cell metabolism, highlighting the significant transformations that occur in GC progression, and suggest possible approaches that may be investigated to more precisely target aberrant B-cell metabolism in SLE.

Toll-like receptor 5 and Toll-like receptor 9 single nucleotide polymorphisms and risk of systemic lupus erythematosus and nephritis in Egyptian patients

Background

Toll-like (TLRs) play a crucial role in both adaptive and innate immunity. The aim of the present study was to assess the association of TLR5-rs5744168, TLR9-rs187084, and TLR9-rs352140 single nucleotide polymorphisms (SNPs) with susceptibility to systemic lupus erythematosus (SLE) and lupus nephritis (LN) in Egyptian patients.

Results

The C allele and homozygous CC genotype of the TLR9-rs352140 in co-dominant and recessive models were more prevalent in SLE patients than controls (P = 0.047, P = 0.017, and P = 0.005 respectively). In contrast, allelic and genotyping distribution of TLR5-rs5744168 and TLR9-rs187084 SNPs showed no association with the risk of SLE. The T allele of the TLR5-rs5744168 was more prevalent in LN patients than controls (P = 0.021). The homozygous TT genotype of TLR5-rs5744168 SNP was more prevalent in LN patients in the co-dominant and the recessive models than controls (P = 0.036 and P = 0.011 respectively). The C allele of the TLR9-rs352140 was more prevalent in LN patients than controls (P = 0.015). The homozygous CC genotype of the TLR9-rs352140 SNP was more prevalent in LN than controls in co-dominant and recessive models (P = 0.002 and P < 0.001). In the recessive model of the TLR5-rs5744168 SNP, the TT genotype was found in 3.2% of the SLE patients while none of the SLE patients without LN or controls had TT genotype (P = 0.036). Also, in the recessive model of the TLR9-rs352140 SNP, the CC genotype was significantly more frequent in SLE patients with LN than without LN (44.4% vs 29.9%, P = 0.045).

Conclusion

Our results support the potential role of TLR5-rs5744168 SNP and TLR9-rs3532140 SNP not only in increasing the risk for development of SLE, but also in increasing the risk of LN in SLE patients among the Egyptian population.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part II): Nucleic acid sensing antagonists and inhibitors

Nucleic acid sensing pathways play an important role in the innate immune system, protecting hosts against infections. However, a large body of evidence supports a close association between aberrant activation of those pathways and autoimmune and inflammatory diseases. Part II of the digest series on small molecule approaches to autoimmune and inflammatory diseases concentrates on recent advances with respect to small molecule antagonists or inhibitors of the nucleic acid sensing pathways, including endosomal TLRs, NLRP3 inflammasome and cGAS-STING.

Genetic and molecular biology of systemic lupus erythematosus among Iranian patients: an overview

BACKGROUND

Systemic lupus erythematosus (SLE) is a clinicopathologically heterogeneous chronic autoimmune disorder affecting different organs and tissues. It has been reported that there is an increasing rate of SLE incidence among Iranian population. Moreover, the Iranian SLE patients have more severe clinical manifestations compared with other countries. Therefore, it is required to introduce novel methods for the early detection of SLE in this population. Various environmental and genetic factors are involved in SLE progression.

MAIN BODY

In present review we have summarized all of the reported genes which have been associated with clinicopathological features of SLE among Iranian patients.

CONCLUSIONS

Apart from the reported cytokines and chemokines, it was interestingly observed that the apoptosis related genes and non-coding RNAs were the most reported genetic abnormalities associated with SLE progression among Iranians. This review clarifies the genetics and molecular biology of SLE progression among Iranian cases. Moreover, this review paves the way of introducing an efficient panel of genetic markers for the early detection and better management of SLE in this population.

Increased expression of Toll-like receptor 7 and 9 in vitiligo melanocytes: a pilot study

BACKGROUND

Toll-like receptors (TLRs) are expressed on human melanocytes, and play an important role in innate and acquired immunity. The role of TLRs in the pathogenesis of vitiligo has not been fully described.

AIM

To investigate the expression of TLRs in melanocytes from patients with vitiligo and healthy controls (HCs).

METHODS

Primary cultured vitiligo and control melanocytes were obtained from perilesional normal skin of patients with generalized vitiligo and HCs. TLRs mRNA expression in melanocytes were determined by real-time reverse transcription PCR and protein expression by western blotting. Apoptosis was analysed using an annexin V-fluorescein isothiocyanate apoptosis detection kit, and tyrosinase activity and melanin content were measured by a modified dopachrome and colorimetric method. Interleukin (IL)-6, IL-8 and soluble cell adhesion molecule (sICAM)-1 expression were measured by ELISA.

RESULTS

In vitiligo melanocytes, compared with control melanocytes, apoptosis rate, expression of TLR7 and TLR9 mRNA and protein, and production of IL-8, IL-6 and sICAM-1 were significantly increased, whereas tyrosinase activity and melanin content were significantly decreased.

CONCLUSIONS

Our results suggest that the increased expression of TLR7 and TLR9 might correlate with melanocyte dysfunction in vitiligo.

Recent clinical trends in Toll-like receptor targeting therapeutics

Toll‐like receptors (TLRs) are germline‐encoded receptors that are central to innate and adaptive immune responses. Owing to their vital role in inflammation, TLRs are rational targets in clinics; thus, many ligands and biologics have been reported to overcome the progression of various inflammatory and malignant conditions and support the immune system. For each TLR, at least one, and often many, drug formulations are being evaluated. Ligands reported as stand‐alone drugs may also be reported based on their use in combinatorial therapeutics as adjuvants. Despite their profound efficacy in TLR‐modulation in preclinical studies, multiple drugs have been terminated at different stages of clinical trials. Here, TLR modulating drugs that have been evaluated in clinical trials are discussed, along with their mode of action, suggestive failure reasons, and ways to improve the clinical outcomes. This review presents recent advances in TLR‐targeting drugs and provides directions for more successful immune system manipulation.

Chronic Inflammation in Immune Aging: Role of Pattern Recognition Receptor Crosstalk with the Telomere Complex?

Age-related decline in immunity is characterized by stem cell exhaustion, telomere shortening, and disruption of cell-to-cell communication, leading to increased patient risk of disease. Recent data have demonstrated that chronic inflammation exerts a strong influence on immune aging and is closely correlated with telomere length in a range of major pathologies. The current review discusses the impact of inflammation on immune aging, the likely molecular mediators of this process, and the various disease states that have been linked with immunosenescence. Emerging findings implicate NF-κB, the major driver of inflammatory signaling, in several processes that regulate telomere maintenance and/or telomerase activity. While prolonged triggering of pattern recognition receptors is now known to promote immunosenescence, it remains unclear how this process is linked with the telomere complex or telomerase activity. Indeed, enzymatic control of telomere length has been studied for many decades, but alternative roles of telomerase and potential influences on inflammatory responses are only now beginning to emerge. Crosstalk between these pathways may prove to be a key molecular mechanism of immunosenescence. Understanding how components of immune aging interact and modify host protection against pathogens and tumors will be essential for the design of new vaccines and therapies for a wide range of clinical scenarios.

Vitamin D3 Alters the Expression of Toll-like Receptors in Peripheral Blood Mononuclear Cells of Patients With Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by production of inflammatory cytokines and autoreactive antibodies due to the loss of immune tolerance. Recognition of self-nucleic acids by intracellular Toll-like receptors (TLRs) can overactivate immune responses and this abnormal activation of TLRs contributes to the pathogenesis of the disease. In recent years, anti-inflammatory and immunomodulatory effects of 1,25-dihydroxyvitamin D3 (VitD3) on the immune system has received particular attention. The present study investigated the effects of vitamin D3 on the expression of TLR3, TLR7, and TLR9 in SLE patients. Study participants included 20 SLE patients and 20 age- and sex-matched healthy controls. Peripheral blood mononuclear cells (PBMCs) were isolated and cultured in the presence or absence of vitamin D3 (50 nM). Then RNA was extracted, cDNA was synthesized and gene expression levels of TLR3, TLR7, and TLR9 were assessed using real-time PCR. Up-regulated expression levels of TLR7 and TLR9 were observed in the PBMCs of SLE patients in comparison with controls. Culturing PBMCs with vitamin D3 significantly down-regulated the expression of TLR3 (8.86 ± 4.2 for SLE patients vs. 45.34 ± 18.6 for control; P = 0.03), TLR7 (17.91 ± 7.7 for SLE patients vs. 242.37 ± 89.6 for controls; P = 0.0001) and TLR9 (4.67 ± 1.9 for SLE patients vs. 8.9 ± 1.5 for controls; P = 0.007) in SLE patients in comparison with healthy controls. The results of the current study suggest that vitamin D3 could exert some of its immunomodulatory effects in SLE patients via affecting the expression levels of some TLRs. J. Cell. Biochem. 118: 4831-4835, 2017. © 2017 Wiley Periodicals, Inc.

Regulating STING in health and disease

The presence of cytosolic double-stranded DNA molecules can trigger multiple innate immune signalling pathways which converge on the activation of an ER-resident innate immune adaptor named "STimulator of INterferon Genes (STING)". STING has been found to mediate type I interferon response downstream of cyclic dinucleotides and a number of DNA and RNA inducing signalling pathway. In addition to its physiological function, a rapidly increasing body of literature highlights the role for STING in human disease where variants of the STING proteins, as well as dysregulated STING signalling, have been implicated in a number of inflammatory diseases. This review will summarise the recent structural and functional findings of STING, and discuss how STING research has promoted the development of novel therapeutic approaches and experimental tools to improve treatment of tumour and autoimmune diseases.

Btk-specific inhibition blocks pathogenic plasma cell signatures and myeloid cell-associated damage in IFN-driven lupus nephritis

Systemic lupus erythematosus (SLE) is often associated with exaggerated B cell activation promoting plasma cell generation, immune-complex deposition in the kidney, renal infiltration of myeloid cells, and glomerular nephritis. Type-I IFNs amplify these autoimmune processes and promote severe disease. Bruton's tyrosine kinase (Btk) inhibitors are considered novel therapies for SLE. We describe the characterization of a highly selective reversible Btk inhibitor, G-744. G-744 is efficacious, and superior to blocking BAFF and Syk, in ameliorating severe lupus nephritis in both spontaneous and IFNα-accelerated lupus in NZB/W_F1 mice in therapeutic regimens. Selective Btk inhibition ablated plasmablast generation, reduced autoantibodies, and - similar to cyclophosphamide - improved renal pathology in IFNα-accelerated lupus. Employing global transcriptional profiling of spleen and kidney coupled with cross-species human modular repertoire analyses, we identify similarities in the inflammatory process between mice and humans, and we demonstrate that G-744 reduced gene expression signatures essential for splenic B cell terminal differentiation, particularly the secretory pathway, as well as renal transcriptional profiles coupled with myeloid cell-mediated pathology and glomerular plus tubulointerstitial disease in human glomerulonephritis patients. These findings reveal the mechanism through which a selective Btk inhibitor blocks murine autoimmune kidney disease, highlighting pathway activity that may translate to human SLE.

MMP2 and MMP9 associate with crescentic glomerulonephritis

Background: Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by multiple organ involvement. Lupus nephritis (LN) is a common manifestation with a wide variety of histological appearances. Matrix metalloproteinases (MMP) 2 and 9 are gelatinases capable of degrading glomerular basement membrane type IV collagen, which have been associated with LN. We examine the expression of MMP2 and MMP9 in different classes of LN.

Methods: MMP2 and MMP9 expression was detected by immunohistochemistry in sections from renal biopsy specimens with class III, class IV and class V LN (total n = 31), crescentic immunoglobulin A nephropathy (n = 6), pauci-immune glomerulonephritis (n = 7), minimal change disease (n = 2), mesangiocapillary glomerulonephritis (n = 7), diabetic nephropathy (n = 12) and histologically normal controls (n = 8).

Results: MMP2 and MMP9 were not expressed in all classes of LN, but were observed in LN with cellular and fibrocellular crescents. MMP2/MMP9 was expressed in cellular and fibrocellular crescents regardless of glomerulonephritis but not observed in inactive fibrous crescents or with mesangial proliferation. This suggests that MMP2 and MMP9 are involved in the development of extracapillary proliferative lesions.

Conclusions: MMP2/MMP9 is expressed with active extracapillary proliferation. Further study is necessary to define whether the expression of MMP2/MMP9 reflects a role in glomerular repair after injury, a role in organ-level immune responses or a role as a marker of epithelialization.

Type I Interferon Inhibition of MicroRNA-146a Maturation Through Up-Regulation of Monocyte Chemotactic Protein-Induced Protein 1 in Systemic Lupus Erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is characterized by the uncontrolled production of inflammatory cytokines, among which type I interferon (IFN) is recognized as a crucial pathogenic factor. The expression of microRNA-146a (miR-146a) is reduced in the white blood cells of SLE patients and accounts for their overactivated inflammatory responses. However, the mechanism of the reduction of miR-146a is still not fully understood. This study was undertaken to test whether the key pathogenic cytokine, type I IFN, is responsible for the dysregulation of miR-146a in SLE.

METHODS

Gene and protein expression was measured in all cells by reverse transcription-quantitative polymerase chain reaction, Northern blotting, or Western blotting. In THP-1 cells, expression of monocyte chemotactic protein-induced protein 1 (MCPIP-1) was knocked down with a lentivirus encoding a short hairpin RNA targeting MCPIP1. The cells were pretreated with type I IFN and assessed for gene expression levels of miR-146a. White blood cells from patients with SLE were analyzed for the expression of the IFN-inducible genes MCPIP1 and miR-146a, and the gene expression data were compared for correlation.

RESULTS

Pretreatment of THP-1 cells with type I IFN attenuated the induction of miR-146a posttranscriptionally, by down-regulating the expression of pre-miR-146a but not pri-miR-146a or its original unspliced transcript. Expression of MCPIP-1, which was enhanced by type I IFN, was found to be responsible for the inhibition of miR-146a. In white blood cells from patients with SLE, MCPIP1 expression was elevated, and its expression correlated positively with the IFN score and negatively with the miR-146a transcript level.

CONCLUSION

Type I IFN inhibits the maturation of miR-146a through the up-regulation of MCPIP-1, and thus contributes to the uncontrolled inflammation and excessive inflammatory gene expression in SLE.

Toll-like receptors and B cells: functions and mechanisms

Numerous reports have described Toll-like receptor (TLR) functions in myeloid cells such as dendritic cells (DCs) and macrophages, but relatively fewer studies have examined TLR responses in B lymphocytes. B cells express a wide variety of TLRs and are highly activated after TLR ligation, leading to enhancements in B cell survival, surface molecule expression, cytokine and antibody production, and antigen presentation. During an immune response, B cells can receive signals through TLRs as well as the B cell antigen receptor (BCR) and/or CD40. TLR ligation synergizes with signals through these receptors and augments both innate and adaptive immune functions of B lymphocytes. Additionally, targeting B cell TLRs may provide new therapies against certain types of cancer as well as autoimmune diseases. Here, we summarize TLR expression and contributions to both normal and pathogenic functions in mouse and human B cells.

Central pathways causing fatigue in neuro-inflammatory and autoimmune illnesses

BACKGROUND

The genesis of severe fatigue and disability in people following acute pathogen invasion involves the activation of Toll-like receptors followed by the upregulation of proinflammatory cytokines and the activation of microglia and astrocytes. Many patients suffering from neuroinflammatory and autoimmune diseases, such as multiple sclerosis, Parkinson's disease and systemic lupus erythematosus, also commonly suffer from severe disabling fatigue. Such patients also present with chronic peripheral immune activation and systemic inflammation in the guise of elevated proinflammtory cytokines, oxidative stress and activated Toll-like receptors. This is also true of many patients presenting with severe, apparently idiopathic, fatigue accompanied by profound levels of physical and cognitive disability often afforded the non-specific diagnosis of chronic fatigue syndrome.

DISCUSSION

Multiple lines of evidence demonstrate a positive association between the degree of peripheral immune activation, inflammation and oxidative stress, gray matter atrophy, glucose hypometabolism and cerebral hypoperfusion in illness, such as multiple sclerosis, Parkinson's disease and chronic fatigue syndrome. Most, if not all, of these abnormalities can be explained by a reduction in the numbers and function of astrocytes secondary to peripheral immune activation and inflammation. This is also true of the widespread mitochondrial dysfunction seen in otherwise normal tissue in neuroinflammatory, neurodegenerative and autoimmune diseases and in many patients with disabling, apparently idiopathic, fatigue. Given the strong association between peripheral immune activation and neuroinflammation with the genesis of fatigue the latter group of patients should be examined using FLAIR magnetic resonance imaging (MRI) and tested for the presence of peripheral immune activation.

SUMMARY

It is concluded that peripheral inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in many patients with neuroimmune and autoimmune diseases.This would also appear to be the case for many patients afforded a diagnosis of Chronic Fatigue Syndrome.

TLR-Dependent Human Mucosal Epithelial Cell Responses to Microbial Pathogens

Toll-like receptor (TLR) signaling represents one of the best studied pathways to implement defense mechanisms against invading microbes in human being as well as in animals. TLRs respond to specific microbial ligands and to danger signals produced by the host during infection, and initiate downstream cascades that activate both innate and adaptive immunity. TLRs are expressed by professional immune cells and by the large majority of non-hematopoietic cells, including epithelial cells. In epithelial tissues, TLR functions are particularly important because these sites are constantly exposed to microorganisms, due to their location at the host interface with the environment. While at these sites specific defense mechanisms and inflammatory responses are initiated via TLR signaling against pathogens, suppression or lack of TLR activation is also observed in response to the commensal microbiota. The mechanisms by which TLR signaling is regulated in mucosal epithelial cells include differential expression and levels of TLRs (and their signaling partners), their cellular localization and positioning within the tissue in a fashion that favors responses to pathogens while dampening responses to commensals and maintaining tissue homeostasis in physiologic conditions. In this review, the expression and activation of TLRs in mucosal epithelial cells of several sites of the human body are examined. Specifically, the oral cavity, the ear canal and eye, the airways, the gut, and the reproductive tract are discussed, along with how site-specific host defense mechanisms are implemented via TLR signaling.

Expression of toll-like receptors 3, 7, and 9 in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown aetiology. The results of experimental studies point to the involvement of innate immunity receptors-toll-like receptors (TLR)-in the pathogenesis of the disease. The aim of the study was to assess the expression of TLR3, 7, and 9 in the population of peripheral blood mononuclear cells (PBMC) and in B lymphocytes (CD19(+)), T lymphocytes (CD4(+) and CD8(+)) using flow cytometry. The study group included 35 patients with SLE and 15 healthy controls. The patient group presented a significantly higher percentage of TLR3- and TLR9-positive cells among all PBMCs and their subpopulations (CD3(+), CD4(+), CD8(+), and CD19(+) lymphocytes) as well as TLR7 in CD19(+) B-lymphocytes, compared to the control group. There was no correlation between the expression of all studied TLRs and the disease activity according to the SLAM scale, and the degree of organ damage according to the SLICC/ACR Damage Index. However, a correlation was observed between the percentage of various TLR-positive cells and some clinical (joint lesions) and laboratory (lymphopenia, hypogammaglobulinemia, anaemia, and higher ESR) features and menopause in women. The results of the study suggest that TLR3, 7, and 9 play a role in the pathogenesis of SLE and have an impact on organ involvement in SLE.

Toll-like receptor (TLR) and matrix metalloproteinase (MMP) polymorphisms and periodontitis susceptibility: a meta-analysis

The aim of this study was to determine whether the toll-like receptor (TLR) and matrix metalloproteinase (MMP) polymorphisms confers susceptibility to periodontitis in ethnically different populations. A literature search using PubMed and Embase provided the data to conduct a meta-analysis on the associations between the TLR2 Arg753Gln, TLR4 Asp299Gly, Thr399Ile, MMP-1 -1607 G1/G2 and MMP-9 -1562 C/T polymorphisms and periodontitis. A total of 32 studies (14 on TLR polymorphisms and 18 on MMP polymorphisms) were considered in the meta-analysis. The meta-analysis showed no association between periodontitis and the TLR2 753Arg allele (Odds ratio [OR]=0.962, 95% confidence interval [CI]=0.662-1.400, p=0.841). Meta-analysis of the TLR4 Asp299Gly and Thr399Ile polymorphisms showed no association between periodontitis and the TLR4 299Asp allele in all study subjects (OR=0.984, 95% CI=0.761-1.271, p=0.900; OR=1.030, 95% CI=0.748-1.418, p=0.854). Meta-analysis showed an association between the MMP-1 -1607 G2G2 genotype and periodontitis in Asians (OR=3.778, 95% CI=1.210-11.80, p=0.022). Meta-analysis containing only studies in Hardy-Weinberg equilibrium revealed no association between chronic periodontitis and the MMP-9 -1562TT genotype (OR=0.638, 95% CI=0.265-1.533, p=0.315). This meta-analysis demonstrates a lack of association between the TLR2 Arg753Gln, TLR4 Asp299Gly, Thr399Ile, MMP-9 -1562 C/T polymorphisms and periodontitis, but shows an association between the MMP-1 -1607 G2G2 genotype and periodontitis in Asians.

Infection and autoimmune disease

Most infectious agents, such as viruses, bacteria and parasites, can trigger autoimmunity via different mechanisms. The development of an autoimmune disorder after infection tends to occur in genetically susceptible individuals. Some parameters, such as genetic predisposition, feature of the infectious agent and sometimes protective effect of the infections, have a significant role in this process. These parameters and various pathogens that could lead to enhancement or exacerbation of autoimmune disease were examined in this review. Recent studies were reviewed from a microbiological perspective.

Association between -1486 T>C and +1174 G>A single nucleotide polymorphisms in TLR9 gene and severity of lupus nephritis

Signaling through Toll-like receptor-9 (TLR9), a mediator of innate immune responses, could have a role in the pathogenesis of systemic lupus erythematosus (SLE). Some studies have shown an association between polymorphisms in the TLR9 gene and disease manifestations. We investigated whether two single nucleotide polymorphisms (-1486 T>C and +1174 G>A) in the TLR9 gene are associated with the risk of renal involvement in SLE. DNA samples from 112 SLE patients (62 with lupus nephritis) and 100 healthy controls were obtained. TLR9 polymorphisms (-1486 T>C and +1174 G>A) were analyzed by polymerase chain reaction–restriction fragment length polymorphism. Genotype and allelic frequencies were compared between lupus patients and healthy controls. Clinical and laboratory manifestations and activity scores on renal biopsy of patients with lupus nephritis were compared between various genotypes. There was no difference in the frequency of genotype or allele distribution at either of the two loci between lupus patients and controls and in lupus patients with or without nephritis. Patients with CC/CT genotype at the -1486 position had higher serum creatinine (P = 0.03) and Austin activity scores (P = 0.015). Patients with AA/AG genotype at +1174 position showed higher serum creatinine (P = 0.04), proteinuria (P = 0.011), anti-dsDNA titers (P < 0.001) and Austin activity scores (P = 0.003) than the GG genotype. Variations at the -1486 and +1174 positions of TLR9 gene are not associated with increased risk of SLE or that of kidney involvement in North Indians. CC/CT genotypes at -1486 and AA/AG at +1174 positions are associated with more severe kidney disease at presentation.

Requirement of myeloid cell-specific Fas expression for prevention of systemic autoimmunity in mice

OBJECTIVE

The death receptor Fas is a critical mediator of the extrinsic apoptotic pathway, and its role in mediating lymphoproliferation has been extensively examined. The present study was undertaken to investigate the impact of myeloid cell-specific loss of Fas.

METHODS

Mice with Fas flanked by loxP sites (Fas(flox/flox) ) were crossed with mice expressing Cre under control of the murine lysozyme M gene promoter (Cre(LysM) ), which functions in mature lysozyme-expressing cells of the myelomonocytic lineage. The genotype for Cre(LysM) Fas(flox/flox) mice was verified by polymerase chain reaction and flow cytometric analysis. Flow cytometric analysis was also used to characterize myeloid, dendritic, and lymphoid cell distribution and activation in bone marrow, blood, and spleen. Luminex-based assays and enzyme-linked immunosorbent assays were used to measure serum cytokine/chemokine and immunoglobulin levels. Renal damage or dysfunction was examined by immunohistochemical and immunofluorescence analysis.

RESULTS

Cre(LysM) Fas(flox/flox) mice exhibited a systemic lupus erythematosus (SLE)-like disease that included leukocytosis, splenomegaly, hypergammaglobulinemia, antinuclear autoantibody and proinflammatory cytokine production, and glomerulonephritis. Loss of Fas in myeloid cells increased levels of both Gr-1(low) and Gr-1(intermediate) blood monocytes and splenic macrophages and, in a paracrine manner, incited activation of conventional dendritic cells and lymphocytes in Cre(LysM) Fas(flox/flox) mice.

CONCLUSION

Taken together, these results suggest that loss of Fas in myeloid cells is sufficient to induce inflammatory phenotypes in mice, reminiscent of an SLE-like disease. Thus, Fas in myeloid cells may be considered a suppressor of systemic autoimmunity.

A model for lupus brain disease

Systemic lupus erythematosus is an autoimmune disease characterized by antibodies that bind target autoantigens in multiple organs in the body. In peripheral organs, immune complexes engage the complement cascade, recruiting blood-borne inflammatory cells and initiating tissue inflammation. Immune complex-mediated activation of Fc receptors on infiltrating blood-borne cells and tissue resident cells amplifies an inflammatory cascade with resulting damage to tissue function, ultimately leading to tissue destruction. This pathophysiology appears to explain tissue injury throughout the body, except in the central nervous system. This review addresses a paradigm we have developed for autoantibody-mediated brain damage. This paradigm suggests that antibody-mediated brain disease does not depend on immune complex formation but rather on antibody-mediated alterations in neuronal activation and survival. Moreover, antibodies only access brain tissue when blood-brain barrier integrity is impaired, leading to a lack of concurrence of brain disease and tissue injury in other organs. We discuss the implications of this model for lupus and for identifying other antibodies that may contribute to brain disease.

Dendritic cells in the circulation of women with preeclampsia demonstrate a pro-inflammatory bias secondary to dysregulation of TLR receptors

Toll-like receptors (TLRs) are central components of the innate immune system that recognize both microbial ligands and host products released during tissue damage. Data from epidemiologic studies and animal models suggest that inappropriate activation of the immune system plays a critical role in the development of preeclampsia. This study evaluates in a systematic fashion the expression and function of TLRs in the circulation of patients with preeclampsia compared to healthy pregnant controls. We evaluated TLR expression and function in primary dendritic cells (DCs) of 30 patients with preeclampsia and 30 gestational age-matched healthy pregnant controls. DCs were stimulated with the different TLR ligands engaging TLR1/2, TLR2/6, TLR3, TLR4, TLR5, TLR7, TLR8 and TLR9. The expression of TLR-induced production of TNF-α, IFN-α, IL-6, and IL-12 were measured by multicolor flow cytometry. Basal expression of TLR3, TLR4 and TLR9 was significantly increased in DCs isolated from women with preeclampsia. Preeclamptic DCs also expressed significantly higher basal levels of cytokines. In contrast, preeclamptic DCs demonstrated a less robust response to stimulation with various TLR ligands as compared with healthy pregnant controls. Under basal conditions, DCs from preeclamptic individuals express higher levels of select TLRs and produce more pro-inflammatory cytokines as compared with healthy controls. As such, the ability of these cells to mount an inflammatory reaction in response to a TLR ligand is limited. These data demonstrate a dysregulated pattern of TLR expression and cytokine production in DCs from PE patients that may limit further activation by TLR engagement.

Mechanisms of tissue injury in lupus nephritis

Systemic lupus erythematosus is a prototypic autoimmune disease characterized by autoantibody production and immune complex formation/deposition in target organs such as the kidney. Resultant local inflammation then leads to organ damage. Nephritis, a major cause of morbidity and mortality in patients with lupus, occurs in approximately 50% of lupus patients. In the present review, we provide an overview of the current research and knowledge concerning mechanisms of renal injury in both lupus-prone mouse models and human lupus patients.

TLR9 in peritoneal B-1b cells is essential for production of protective self-reactive IgM to control Th17 cells and severe autoimmunity

The role of TLR9 in the development of the autoimmune disease systemic lupus erythematosus is controversial. In different mouse models of the disease, loss of TLR9 abolishes the generation of anti-nucleosome IgG autoantibodies but at the same time exacerbates lupus disease. However, the TLR9-dependent tolerance mechanism is unknown. In this study, we show that loss of TLR9 is associated with low peritoneal B-1b cell numbers and low levels of protective self-reactive IgM serum autoantibodies in lupus-prone FcγRIIB-deficient mice leading to the uncontrolled accumulation of proinflammatory CD4(+) cells and exacerbated autoimmunity. TLR7 signaling was not able to compensate for the loss of TLR9 signaling in peritoneal B-1b cells to induce IgM Abs. Transfer of TLR9-expressing peritoneal B-1b cells from FcγRIIB-deficient mice or of recombinant monoclonal self-reactive IgM Abs was sufficient to reduce the frequency of proinflammatory Th17 cells and lupus disease in FcγRIIB/TLR9 double-deficient mice. Taken together, these data provide evidence for a TLR9-dependent tolerance mechanism of peritoneal B-1b cells generating protective self-reactive IgM in lupus-prone mice to control Th17 cell development and severe autoimmunity.

Are Toll-like receptors and decoy receptors involved in the immunopathogenesis of systemic lupus erythematosus and lupus-like syndromes?

In this paper we focus our attention on the role of two families of receptors, Toll-like receptors (TLR) and decoy receptors (DcR) involved in the generation of systemic lupus erythematosus (SLE) and lupus-like syndromes in human and mouse models. To date, these molecules were described in several autoimmune disorders such as rheumatoid arthritis, antiphospholipids syndrome, bowel inflammation, and SLE. Here, we summarize the findings of recent investigations on TLR and DcR and their role in the immunopathogenesis of the SLE.

Essential role for the prolyl isomerase Pin1 in Toll-like receptor signaling and type I interferon-mediated immunity

Toll-like receptors (TLRs) shape innate and adaptive immunity to microorganisms. The enzyme IRAK1 transduces signals from TLRs, but mechanisms for its activation and regulation remain unknown. We found here that TLR7 and TLR9 activated the isomerase Pin1, which then bound to IRAK1; this resulted in activation of IRAK1 and facilitated its release from the receptor complex to activate the transcription factor IRF7 and induce type I interferons. Consequently, Pin1-deficient cells and mice failed to mount TLR-mediated, interferon-dependent innate and adaptive immune responses. Given the critical role of aberrant activation of IRAK1 and type I interferons in various immune diseases, controlling IRAK1 activation via inhibition of Pin1 may represent a useful therapeutic approach.

MicroRNA, a new paradigm for understanding immunoregulation, inflammation, and autoimmune diseases

MicroRNAs (miRNAs) are newly discovered, small, noncoding ribonucleic acids (RNAs) that play critical roles in the regulation of host genome expression at the posttranscriptional level. During last 20 years, miRNAs have emerged as key regulators of various biological processes including immune cell lineage commitment, differentiation, maturation, and maintenance of immune homeostasis and normal function. Thus, it is not surprising that dysregulated miRNA expression patterns now have been documented in a broad range of diseases including cancer as well as inflammatory and autoimmune diseases. This rapidly emerging field has revolutionized our understanding of normal immunoregulation and breakdown of self-tolerance. This review focuses on the current understanding of miRNA biogenesis, the role of miRNAs in the regulation of innate and adaptive immunity, and the association of miRNAs with autoimmune diseases. We have discussed miRNA dysregulation and the potential role of miRNAs in systemic lupus erythematosus (SLE), rheumatoid arthritis, and multiple sclerosis. Given that most autoimmune diseases are female-predominant, we also have discussed sex hormone regulation of miRNAs in inflammatory responses, with an emphasis on estrogen, which now has been shown to regulate miRNAs in the immune system. The field of miRNA regulation of mammalian genes has tremendous potential. The identification of specific miRNA expression patterns in autoimmune diseases as well as a comprehensive understanding of the role of miRNA in disease pathogenesis offers promise of not only novel molecular diagnostic markers but also new gene therapy strategies for treating SLE and other inflammatory autoimmune diseases.

Fungal pathogen recognition by scavenger receptors in nematodes and mammals

Macrophages are important cells in the host resistance to fungal infections, and fungal recognition by macrophages triggers phagocytosis, intracellular killing, induction of inflammatory cytokines and chemokines, and initiation of the adaptive immune response. All of the receptors that mediate binding and engulfment of fungal pathogens and the signaling pathways triggered by fungal pathogens that regulate anti-fungal immunity are not fully understood. Using an RNAi screen we recently demonstrated that the C. elegans receptors CED-1 and C03F11.3, and their mammalian orthologues, the scavenger receptors SCARF1 and CD36 mediate host defense against the fungal pathogen, Cryptococcus neoformans. Finally, SCARF1 and CD36 function as co-receptors by binding and engulfing fungal pathogens to facilitate Toll-like receptor 2 signaling. Here we will summarize and expand upon our previous findings.

Autoimmunity and chronic inflammation - two clearance-related steps in the etiopathogenesis of SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease with very prominent chronic inflammatory aspects that render into multiple symptoms and clinical signs. The precise etiology of SLE remains elusive; however, it is known that its etiopathogenesis is of multifactorial nature. The production of autoantibodies (AAb) targeting double stranded DNA (dsDNA) and other nuclear autoantigens is the main characteristic of this disease. These target antigens are often modified and/or translocated when apoptotic cells undergo secondary necrosis as a consequence of the clearance deficiency in patients with SLE. In healthy individuals, dead and dying cells are rapidly removed by macrophages in an anti-inflammatory context; this does not elicit immune responses. In SLE, apoptotic cells are often not properly cleared; autoantigens leak out, and are subsequently presented to B cells by follicular dendritic cells (FDC) in secondary lymphoid tissues. This defect challenges the peripheral self-tolerance. Autoreactive B cell activation and production of anti-nuclear AAb result as the first step in the etiopathogenesis of SLE. The second step is the formation of immune complexes (IC) with apoptotic cell-derived nuclear remnants either in situ or deposited in various tissues. Nucleic acid-containing IC may also be ingested by phagocytes, which subsequently produce pro-inflammatory cytokines. Both processes result in chronic organ and tissue damage, development and maintenance of the systemic autoimmune disease. In conclusion, clearance deficiency may contribute to SLE in two ways: first, in germinal centres it enables the affinity maturation of autoreactive B cells and second, in peripheral tissues it leads to the accumulation of accessible nuclear autoantigens. Chronic inflammation in SLE is consequently promoted by the persistently binding of AAb with their cognate autoantigens forming a binary weapon: the nucleic acid-containing IC.

Dendritic cell function in lupus: Independent contributors or victims of aberrant immune regulation

Dendritic cells (DCs) represent an important component of the immune system connecting the innate and adaptive immune responses. They are able to trigger strong immunity as well as tolerance against certain antigens, and therefore it is obvious that they have a central role in the expression of immunological diseases. However, because DCs are sparse, heterogeneous and plastic, their exact role in complex autoimmune diseases, such as systemic lupus erythematosus (SLE) remains not well defined. In this review, we make an attempt to summarize critically recent knowledge on the role of conventional DCs in the expression of autoimmunity and pathology in SLE.

Genetic associations in type I interferon related pathways with autoimmunity

Type I interferons play an outstanding role in innate and adaptive immunity by enhancing functions of dendritic cells, inducing differentiation of monocytes, promoting immunoglobulin class switching in B cells and stimulating effector functions of T cells. The increased production of IFNα/β by plasmacytoid dendritic cells could be responsible for not only efficient antiviral defence, but it also may be a pathological factor in the development of various autoimmune disorders. The first evidence of a genetic link between type I interferons and autoimmune diseases was the observation that elevated IFNα activity is frequently detected in the sera of patients with systemic lupus erythematosus, and that this trait shows high heritability and familial aggregation in their first-degree healthy relatives. To date, a number of genes involved in interferon signalling have been associated with various autoimmune diseases. Patients with systemic lupus erythematosus, Sjögren's syndrome, dermatomyositis, psoriasis, and a fraction of patients with rheumatoid arthritis display a specific expression pattern of interferon-dependent genes in their leukocytes, termed the interferon signature. Here, in an attempt to understand the role of type I interferons in the pathogenesis of autoimmunity, we review the recent advances in the genetics of autoimmune diseases focusing on the association of genes involved in type I interferon pathways.

Pathogenesis of human systemic lupus erythematosus: recent advances

Systemic lupus erythematosus (SLE) is an autoimmune disease with manifestations derived from the involvement of multiple organs including the kidneys, joints, nervous system and hematopoietic organs. Immune system aberrations, as well as heritable, hormonal and environmental factors interplay in the expression of organ damage. Recent contributions from different fields have developed our understanding of SLE and reshaped current pathogenic models. Here, we review recent findings that deal with (i) genes associated with disease expression; (ii) immune cell molecular abnormalities that lead to autoimmune pathology; (iii) the role of hormones and sex chromosomes in the development of disease; and (iv) environmental and epigenetic factors thought to contribute to the expression of SLE. Finally, we highlight molecular defects intimately associated with the disease process of SLE that might represent ideal therapeutic targets and disease biomarkers.

The role of toll-like receptors in host defenses and their relevance to dermatologic diseases

The family of toll-like receptors (TLRs) plays a central role in the cutaneous immune defense system. To date, different TLRs have been found on several major cell populations of the skin, such as keratinocytes, fibroblasts, antigen-presenting cells, and melanocytes. Activation of TLRs leads, via different intracellular signaling pathways, to the production of pro-inflammatory stimuli, and is considered a danger signal that should transform the skin in to the functional state of defense. However, TLRs have also been implicated in tissue homeostasis and renewal. Within the group of TLRs, two types have been identified: surface-expressed TLRs, which are predominantly active against bacterial cell wall compounds; and intracellular receptors, which preferentially recognize virus-associated pattern molecules. In addition, surface-expressed receptors trigger phagocytotic and maturation signals, while the intracellular TLRs lead to the induction of antiviral genes. Our review aims to outline the importance of TLRs in the pathogenesis of numerous skin diseases and the potential of TLR agonists as a treatment option for various skin diseases.

Ro60-associated single-stranded RNA links inflammation with fetal cardiac fibrosis via ligation of TLRs: a novel pathway to autoimmune-associated heart block

Activation of TLR by ssRNA after FcgammaR-mediated phagocytosis of immune complexes (IC) may be relevant in autoimmune-associated congenital heart block (CHB) where the obligate factor is a maternal anti-SSA/Ro Ab and the fetal factors, protein/RNA on an apoptotic cardiocyte and infiltrating macrophages. This study addressed the hypothesis that Ro60-associated ssRNAs link macrophage activation to fibrosis via TLR engagement. Both macrophage transfection with noncoding ssRNA that bind Ro60 and an IC generated by incubation of Ro60-ssRNA with an IgG fraction from a CHB mother or affinity purified anti-Ro60 significantly increased TNF-alpha secretion, an effect not observed using control RNAs or normal IgG. Dependence on TLR was supported by the significant inhibition of TNF-alpha release by IRS661 and chloroquine. The requirement for FcgammaRIIIa-mediated delivery was provided by inhibition with an anti-CD16a Ab. Fibrosis markers were noticeably increased in fetal cardiac fibroblasts after incubation with supernatants generated from macrophages transfected with ssRNA or incubated with the IC. Supernatants generated from macrophages with ssRNA in the presence of IRS661 or chloroquine did not cause fibrosis. In a CHB heart, but not a healthy heart, TLR7 immunostaining was localized to a region near the atrioventricular groove at a site enriched in mononuclear cells and fibrosis. These data support a novel injury model in CHB, whereby endogenous ligand, Ro60-associated ssRNA, forges a nexus between TLR ligation and fibrosis instigated by binding of anti-Ro Abs to the target protein likely accessible via apoptosis.

Apo material as a trigger for inflammation in systemic lupus erythematosus

While several characteristics of systemic lupus erythematosus (SLE) have been investigated, the distinct pathogenetic mechanisms leading to autoimmunity and chronic inflammation are not understood yet. A central role for apo has been implicated in the pathogenesis of SLE and an increased rate of apo or a defective clearance of apo cells have repeatedly been described in SLE patients, which show elevated levels of alpha-interferon (alphaIFN) as well as an enhanced expression of alphaIFN-alpha inducible genes referred to as alphaIFN signature. Recent publications link alphaIFN and apo: apo cell-derived microparticles can directly stimulate plasmacytoid dendritic cells to secret alphaIFN. This review highlights the role of apo material as source for AAg and as a trigger for chronic inflammation in the pathogenesis of SLE.

Identification of IRAK1 as a risk gene with critical role in the pathogenesis of systemic lupus erythematosus

A combined forward and reverse genetic approach was undertaken to test the candidacy of IRAK1 (interleukin-1 receptor associated kinase-1) as an X chromosome-encoded risk factor for systemic lupus erythematosus (SLE). In studying approximately 5,000 subjects and healthy controls, 5 SNPs spanning the IRAK1 gene showed disease association (P values reaching 10(-10), odds ratio >1.5) in both adult- and childhood-onset SLE, in 4 different ethnic groups, with a 4 SNP haplotype (GGGG) being strongly associated with the disease. The functional role of IRAK1 was next examined by using congenic mouse models bearing the disease loci: Sle1 or Sle3. IRAK1 deficiency abrogated all lupus-associated phenotypes, including IgM and IgG autoantibodies, lymphocytic activation, and renal disease in both models. In addition, the absence of IRAK1 reversed the dendritic cell "hyperactivity" associated with Sle3. Collectively, the forward genetic studies in human SLE and the mechanistic studies in mouse models establish IRAK1 as a disease gene in lupus, capable of modulating at least 2 key checkpoints in disease development. This demonstration of an X chromosome gene as a disease susceptibility factor in human SLE raises the possibility that the gender difference in SLE may in part be attributed to sex chromosome genes.

Prevention of autoimmune disease by induction of tolerance to Toll-like receptor 7

Activation of Toll-like receptors (TLR) contributes to the initiation and maintenance of chronic inflammation in autoimmune diseases, yet repeated exposure to a TLR agonist can induce hyporesponsiveness to subsequent TLR stimulation. Here, we used a synthetic TLR7 agonist, 9-benzyl-8-hydroxy-2-(2-methoxyethoxy) adenine (SM360320, 1V136) to study TLR7 induced attenuation of inflammatory responses and its application to autoimmune diseases. Repeated low dose administration of this TLR7 agonist induced hyporesponsiveness or tolerance to TLR2, -7, and -9 activators and limited the course of neural inflammation in an experimental allergic encephalomyelitis model. The hyporesponsiveness did not depend on T or B lymphocytes, but did require bone marrow derived cells. In addition, TLR7 tolerance reduced inflammation in a passive antibody mediated arthritis model. TLR7 tolerance did not cause global immunosuppression, because susceptibility to Listeria monocytogenes infection was not altered. The mechanism of TLR7 tolerance involved the up-regulation of 2 inhibitors of TLR signaling: Interleukin 1 Receptor Associated Kinase (IRAK) M, and Src homology 2 domain-containing inositol polyphosphate phosphatase (SHIP)-1. These findings suggest that induction of TLR7 tolerance might be a new therapeutic approach to subdue inflammation in autoimmune diseases.

The contribution of direct TLR signaling to T cell responses

It is well established that Toll-like receptors (TLRs) play a critical role in the generation of innate immune responses and thereby also play an important, indirect role in the initiation of subsequent adaptive T cell responses. However, T cells also express certain TLRs, and we have focused on the physiological importance of direct TLR signaling in T cells. TLRs can function as co-stimulatory receptors that complement TCR-induced signals to enhance effector T cell proliferation, survival and cytokine production. We also found that TLR signaling pathways in T cells are required for the effective clonal expansion of antigen-specific T cells during infection in vivo. Thus, the importance of TLRs in T cell-mediated immunity reflects both T cell-extrinsic and T cell-intrinsic components, which warrants a reconsideration of the dogma that restricts germ-line encoded pattern recognition to cells of the innate immune system.

Antigen-specific responses and ANA production in B6.Sle1b mice: a role for SAP

B6.Sle1b mice, which contain the Sle1b gene interval derived from lupus prone NZM2410 mice on a C57BL/6 background, present with gender-biased, highly penetrant anti-nuclear antibody (ANA) production. To obtain some insight into the possible induction mechanism of autoantibodies in these mice we compared antigen-specific T dependent (TD) and T independent (TI-II) responses between B6.Sle1b and B6 mice before the development of high ANA titers. Our results show that B6.Sle1b mice mount enhanced responses to a TI-II antigen. Additionally, the memory T cell response generated by a TD antigen also increased. This enhancement correlates with the greater ability of B cells from B6.Sle1b mice to present antigen to T cells. The SLAM Associated Protein (SAP) is critical for signaling of many of the molecules encoded by the SLAM/CD2 gene cluster, candidates for mediating the Sle1b phenotype; therefore, we also investigated the effect of sap deletion in these strains on the TD and TI-II responses as well as on ANA production. The results of these studies of responses to non-self-antigens provide further insight into the mechanism by which responses to self-antigens might be initiated in the context of specific genetic alterations.

B cells flying solo

Systemic autoimmunity such as systemic lupus erythematosus (SLE) is associated with the loss of B-cell tolerance, B-cell dysregulation and autoantibody production. While some autoantibodies may contribute to the pathology seen with SLE, numerous studies have shown that dysregulation of T-cell function is another critical aspect driving disease. The positive results obtained in clinical trials using T-cell- or B-cell-specific treatments have suggested that cooperation between T and B cells probably underlies disease progression in many patients. A similar cooperative mechanism seemed to explain SLE developing in mice overexpressing the B-cell-activating factor from the tumor necrosis factor family (BAFF). However, surprisingly, T-cell-deficient BAFF transgenic (Tg) mice develop SLE similar to T-cell-sufficient BAFF Tg mice, and the disease was linked to innate activation of B cells and production of proinflammatory autoantibody isotypes. In conclusion, dysregulated innate activation of B cells alone can drive disease independently of T cells, and as such this aspect represents a new pathogenic mechanism in autoimmunity.

Therapeutic impact of toll-like receptors on inflammatory bowel diseases: a multiple-edged sword

Recent studies have begun to define the mechanisms through which Toll-like receptors (TLRs) regulate intestinal homeostasis in health and disease. Current therapies for inflammatory bowel diseases (IBDs) mostly aim at interrupting the inflammatory cascade through agents that regulate TH1 or TH2 cytokine responses. As recognition grows for TLR dysfunction to play a role in IBD pathogenesis, TLRs could provide another valid interventional target for novel therapy development. However, seemingly contradictory results from studying different murine models of colitis have so far confounded whether therapeutically useful modulation of TLRs is best accomplished by activating, inhibiting, or rather a combination of both at different stages of mucosal disease. This review evaluates potential strategies as well as their rationale and future prospects.