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The Potential Role of Th17 in Mediating the Transition from Acute to Chronic Autoimmune Inflammation: Rheumatoid Arthritis as a Model


Does Periodontopathic Bacterial Infection Contribute to the Etiopathogenesis of the Autoimmune Disease Rheumatoid Arthritis?

Abstract: There is a significant association between rheumatoid arthritis (RA) and periodontal disease (PD). Patients with longstanding active RA have been found to have a substantially increased frequency of PD compared with healthy subjects. Further, patients with PD have been shown to have a higher prevalence of RA than patients without periodontitis. Antibodies to Gram-negative, anaerobic periodontal pathogens such as Porphyromonas gingivalis, Prevotella intermedia, Prevotella melaninogenica, and Tannerella forsythia have been detected in the serum and synovial fluid of RA patients. These pathogens have also been identified in the synovial fluid of RA patients, with higher levels of bacterial DNA in RA patients than in controls. This review examines the association between periodontopathic bacteria and the etiology of RA. ... Read more

Targeting B Cells for the Treatment of SLE: The Beginning of the End or the End of the Beginning?

Abstract: Systemic Lupus Erythematosus (SLE) is a systemic autoimmune disease for which therapeutic advances in immunosuppressive and support therapy have significantly improved survival over the last 5 decades. Unfortunately, SLE still carries substantially increased rates of mortality and end stage renal disease which are even more elevated in younger patients. No new drugs have been approved for SLE in over 50 years. Hence, a lot of hope and excitement has been generated by the development of biological agents designed to eliminate B cells either through direct killing (anti-B cell antibodies such as rituximab) or attrition by inhibition of survival (anti-BLyS/BAFF agents such as belimumab). Indeed a strong rationale for targeting B cells in SLE is supported by the major pathogenic roles they play in SLE through both autoantibody production and multiple antibody-independent functions. These hopes, however, have been darted by the failure of two different phase III randomized placebo-controlled trials of rituximab. Yet, clinicians continue to use rituximab off-label with the belief that it provides significant benefit and can rescue patients with disease that is refractory to current modalities. Moreover, recent positive results of two large controlled trials of belimumab have restored confidence that B cell targeting may after all be of benefit in SLE. In this review we discuss the background and rationale for the use of anti-B cell agents in SLE, review the available results, and provide models that could help reconcile the opposing results observed in different studies. These models could also help frame the design and evaluation of current and future B cell therapies. ... Read more

Role of the IL-23/IL-17 Axis in Crohn's Disease

Abstract: Crohn's disease is an immune-mediated disease that is characterized by chronic intestinal inflammation. Effector CD4+ T-lymphocytes are expanded in Crohn's disease-associated inflammatory lesions and play a critical role in the pathogenesis of this condition. Recently, a novel population of effector T-lymphocytes has been identified, which is clearly separated from the traditional Th1 and Th2 lineages and is characterized by the secretion of IL-17, hence its designation as Th17. The development of this population has been closely linked to IL-23, a member of the IL-12 family of cytokines. Converging lines of evidence support the hypothesis that the IL-23/Th17 axis is of pathogenic relevance for Crohn's disease. Protein and mRNA levels of IL-23, IL-17, and other Th17 effector cytokines, such as IL-21 and IL-22, are elevated in areas with active Crohn's disease-related inflammation, whereas lamina propria mononuclear cells from patients with Crohn's disease secrete increased amounts of IL-17 upon T-cell receptor-specific stimulation. Genome-wide association studies have identified several Crohn's disease-associated polymorphisms in genes that encode for proteins of the IL-23/Th17 pathway. Functional studies have shown that Th17-related effector cytokines induce pro-inflammatory responses that are components of the pathogenetic mechanisms of Crohn's disease, including recruitment of neutrophils via IL-8 induction, upregulation of inflammatory mediators such as TNF-α, IL-1β, and IL-6, and secretion of metalloproteinases by intestinal fibroblasts. Finally, in several animal models of intestinal inflammation, disease severity is ameliorated when the IL-23/Th17 pathway is rendered deficient. These findings point to a critically important role for IL-23/Th17-mediated immune responses in Crohn's disease pathogenesis and may offer unique therapeutic opportunities for patients. ... Read more

Macrophage Subpopulations in Systemic Lupus Erythematosus

Abstract: Systemic lupus erythematosus (SLE) is a heterogeneous group of autoimmune disorders defined by a consensus of clinical and laboratory criteria. Much of the pathophysiology and therapy of SLE has focused on autoimmune B and T cells of the adaptive immune system. Recently, the role of macrophages, part of the innate immune system, in SLE pathogenesis has gained attention. The field of immunology in general has recently changed in the way that it approaches macrophages. Rather than viewing them as a single, concrete whole, it has become clear that different subpopulations of macrophages contribute to various immune and non-immune processes. Such a nomenclature may provide an ideal framework from which to study macrophage pathogenesis in SLE. Studies suggest that M1 subtype macrophages play an important inflammatory role in SLE pathogenesis. Further, apparently reduced populations of M2a and M2c subtype macrophages may contribute to the lack of anti-inflammatory activity apparent in the disease. M2b subtype macrophages may actually have a role in causing disease directly. Regulatory macrophages have yet to be explored thoroughly in SLE, though the presence of a few of their markers may mean that they are active in suppressing SLE-related inflammation. ... Read more

Understanding Autoimmunity in the Eye: From Animal Models to Novel Therapies

Abstract: In recent years considerable headway has been made on understanding the mechanisms underlying inflammatory diseases of the eye. This includes the role of the innate vs. adaptive arms of the immune systems in disease, the concept that distinct immune pathways can drive end-organ pathology, and the role as well as limitations of immune privilege in controlling the innate and adaptive effector responses that lead to eye pathology and loss of vision. These insights have largely been derived from basic studies in established and in newly developed animal models of uveitis. The increased understanding of disease mechanisms has the potential to guide development of rational therapies for human uveitis. Many novel biologics currently in use or being evaluated have been developed, or validated, in animal models of autoimmune and inflammatory disease, including experimental uveitis. Paradoxically, and fueled in part by dwindling research budgets, a campaign has been gathering momentum against use of animal models in preclinical research, as being poorly representative of responses in humans. Given the extensive genetic similarity between humans and laboratory rodents as revealed by the Human, Mouse and Rat Genome Projects, and the finding that almost all known disease-associated genes have orthologs in mice and rats, perhaps the problem is our still-insufficient understanding of mechanisms and inadequate knowledge of species differences, resulting in poor choice of models, rather than in an inherent unsuitability of animal models to represent human disease. ... Read more

B-cell Lymphomagenesis in Autoimmune Diseases: the Missing Links

Abstract: Patients with autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome have an increased risk of developing B-cell non-Hodgkin's lymphomas but the mechanisms behind this phenomenon remain unknown. By focusing on recent research reports we explore and discuss some of the proposed mechanisms that contribute to this link. The complexity is enormous and can involve genetic and environmental factors, chronic immune stimulation by antigens, and even the treatment for these autoimmune diseases. These mechanisms can be combined in different ways causing great variability in one's predisposition to lymphomagenesis. Knowing more about these pathways is urgent. The more we know about autoimmune diseases the better we can treat our patients effectively and the more we can prevent lymphomas from developing. ... Read more

T Cell Chemokine Receptor Patterns as Pathogenic Signatures in Autoimmunity

Abstract: Autoimmune diseases arise from aberrant activation of immune cells directed against endogenous autoantigens expressed throughout the human body. While the initiating triggers remain poorly understood, the self-perpetuating phase of these diseases is directly linked to the ongoing recruitment of inflammatory cells that traffic to the affected anatomical sites. T lymphocytes are prominent drivers of many autoimmune diseases and the targeted trafficking of these cells to infiltrate the affected organs is often a common denominator. The regulation of T cell trafficking involves the coordinated expression of specific patterns of chemokines and the reciprocal expression of cognate chemokine receptors on T cell membranes. Thereby, chemokines direct the specific trafficking of a wide array of responsive activated immune cells. Specific patterns of chemokine receptor expression can correlate with disease activity in an autoimmune disease, confirming the importance of further characterizing the T cells that infiltrate specific sites of autoimmunity. Herein, we will review our current understanding of the roles of chemokines in two common autoimmune diseases: rheumatoid arthritis and multiple sclerosis. We also discuss the implications for chemokine receptor signatures in autoimmune pathogenesis, and how these may provide novel targets for therapeutic intervention. ... Read more

Immune Mechanisms in Atherosclerosis and Potential for an Atherosclerosis Vaccine

Abstract: A large body of evidence implicates the immune system in the pathogenesis and modulation of atherosclerosis. Dendritic cells and lymphocytes are among the many components of the immune system that are involved in modulating atherogenesis. This review focuses on the current knowledge of the complex role of the dendritic cells and lymphocytes in atherogenesis and the potential for immune-modulation therapies for atherosclerosis. ... Read more

A Role for Lysophosphatidic Acid and Sphingosine 1-Phosphate in the Pathogenesis of Systemic Sclerosis

Abstract: Systemic sclerosis (SSc) is a complex fibrosing autoimmune disease that has variable clinical manifestations and morbidity/mortality secondary to organ damage due to vasculopathy and/or fibrosis. Initial events in the pathogenesis are manifested by fibroproliferative vasculopathy that compromises delivery of blood to critical organs. There is evidence of autoimmunity early in the disease which persists and is accompanied by fibrotic processes that leave large accumulations of collagen and other matrix components in the intima of blood vessels and extracellularly in the connective tissue of organs affected by the disease. It has recently been realized that the lysophospholipids -- lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), which are elevated in sera of SSc patients, are capable of producing many of the abnormalities observed in the vasculature, immune system, and connective tissue of patients with this disease. This article reviews key abnormalities of the vasculature, immune system, and connective tissue in SSc that could be mediated by LPA/S1P. ... Read more

New Insight in the Mechanism of Action of Rituximab: The Interferon Signature Towards Personalized Medicine

Abstract: Rheumatoid arthritis (RA) is the most common chronic inflammatory disorder of the musculoskeletal system that may cause permanent joint damage. The disease has a major impact on the quality of life of affected individuals, costs for the health care system, and society. Currently, no curative treatment is available, and patients are subjected to a prolonged course of treatment. Due to their role in the pathogenesis of RA, B cells have become an attractive target for therapy. Rituximab (Mabthera®/Rituxan®) is a therapeutic monoclonal antibody against CD20 expressed on B cells, which is effective in depleting B cells and approved worldwide for the treatment of RA. Rituximab was shown to be highly beneficial in decreasing clinical symptoms, safe, and well tolerated. However, clinical experience revealed that approximately 30-40% of RA patients do not respond to it. Given the destructive nature of RA, the risk of adverse effects, and considerable costs for therapy, there is a strong need to make predictions on the clinical outcome before the start of therapy. Since nearly all treated patients experience an effective depletion of circulating B cells, questions have been raised concerning the mechanism of action. In this review, novel developments, in particular the findings on the role of the interferon system, will be highlighted. This may add new and important information to our understanding of the mechanism that underlies the clinical outcome of rituximab treatment and may lead to the identification of biomarkers to predict the response. ... Read more

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