Intravenously applied IgG stimulates complement attenuation in a complement-dependent autoimmune disease at the amplifying C3 convertase level

Complement activation negatively affects the platelet response to thrombopoietin receptor agonists in patients with immune thrombocytopenia: a prospective cohort study

Increased platelet destruction is central in the pathogenesis of immune thrombocytopenia. However, impaired platelet production is also relevant and its significance underlies the rationale for treatment with thrombopoietin receptor agonists (TPO-RAs). Previous studies have associated enhanced complement activation with increased disease severity. Additionally, treatment refractoriness has been demonstrated to resolve by the administration of complement-targeted therapeutics in a subset of patients. The association between complement activation and the platelet response to TPO-RA therapy has previously not been investigated. In this study, blood samples from patients with immune thrombocytopenia (n = 15) were prospectively collected before and two, six and 12 weeks after the initiation of TPO-RA therapy. Plasma levels of complement degradation product C4d and soluble terminal complement complexes were assessed. Patients with significantly elevated baseline levels of terminal complement complexes exhibited more often an inadequate platelet response (p = .04), were exclusively subjected to rescue therapy with intravenous immunoglobulin (p = .02), and did not respond with a significant platelet count increase during the study period. C4d showed a significant (p = .01) ability to distinguish samples with significant terminal complement activation, implying engagement of the classical complement pathway. In conclusion, elevated levels of complement biomarkers were associated with a worse TPO-RA treatment response. Larger studies are needed to confirm these results. Biomarkers of complement activation may prove valuable as a prognostic tool to predict which patients that potentially could benefit from complement-inhibiting therapy in the future.

Intravenous Immunoglobulin: Mechanism of Action in Autoimmune and Inflammatory Conditions

Intravenous immunoglobulin (IVIG) is the mainstay of therapy for humoral immune deficiencies and numerous inflammatory disorders. Although the use of IVIG may be supplanted by several targeted therapies to cytokines, the ability of polyclonal normal IgG to act as an effector molecule as well as a regulatory molecule is a clear example of the polyfunctionality of IVIG. This article will address the mechanism of action of IVIG in a number of important conditions that are otherwise resistant to treatment. In this commentary, we will highlight mechanistic studies that shed light on the action of IVIG. This will be approached by identifying effects that are both common and disease-specific, targeting actions that have been demonstrated on cells and processes that represent both innate and adaptive immune responses.

Efficacy of intravenous immunoglobulin (IVIg) on COVID-19-related neurological disorders over the last 2 years: an up-to-date narrative review

Introduction

Among the clinical manifestations of SARS-CoV-2 infection, neurological features have been commonly reported and the state-of-the-art technique suggests several mechanisms of action providing a pathophysiological rationale for central and peripheral neurological system involvement. However, during the 1st months of the pandemic, clinicians were challenged to find the best therapeutic options to treat COVID-19-related neurological conditions.

Methods

We explored the indexed medical literature in order to answer the question of whether IVIg could be included as a valid weapon in the therapeutic arsenal against COVID-19-induced neurological disorders.

Results

Virtually, all reviewed studies were in agreement of detecting an acceptable to great efficacy upon IVIg employment in neurological diseases, with no or mild adverse effects. In the first part of this narrative review, the interaction of SARS-CoV-2 with the nervous system has been discussed and the IVIg mechanisms of action were reviewed. In the second part, we collected scientific literature data over the last 2 years to discuss the use of IVIg therapy in different neuro-COVID conditions, thus providing a summary of the treatment strategies and key findings.

Discussion

Intravenous immunoglobulin (IVIg) therapy is a versatile tool with multiple molecular targets and mechanisms of action that might respond to some of the suggested effects of infection through inflammatory and autoimmune responses. As such, IVIg therapy has been used in several COVID-19-related neurological diseases, including polyneuropathies, encephalitis, and status epilepticus, and results have often shown improvement of symptoms, thus suggesting IVIg treatment to be safe and effective.

Serum C3 complement levels predict prognosis and monitor disease activity in Guillain-Barré syndrome

OBJECTIVE

Biomarkers are needed to predict prognosis and disease activity in patients with Guillain-Barré syndrome (GBS). The complement system is a key player in the pathogenesis of GBS. This study aimed to assess the potential utility of serum complement proteins as novel biomarkers in GBS.

METHODS

We reviewed the medical records of 76 GBS patients with C3 and C4 measurements during hospitalization between 2010 and 2021. Clinical outcomes were correlated with baseline serum C3, C4, and seven additional predictors: four existing biomarkers (GM1, albumin, immunoglobulin G, neutrophil-lymphocyte ratio) and three clinical factors from the modified Erasmus GBS outcome score model. Five complement activation products (C3a, C4a, C5a, soluble C5b-9, factor Bb) were measured in 35 patients and were compared with C3 and C4 levels. Longitudinal changes in C3 and C4 levels were compared with the disease course in 12 patients.

RESULTS

Higher C3, but not C4, was associated with poorer outcomes: lower Medical Research Council sum scores (MRCSS), higher GBS disability score (GBSDS), longer hospitalization, and more frequent treatment-related fluctuations. Age, MRCSS at admission, and baseline serum C3 were significant independent indicators of 1- and 3-month GBSDS. We found that C3 was positively correlated with C3a (r = 0.32) and C5a (r = 0.37), which indicates an activated complement cascade with high C3. Longitudinal change of C3 coincided with clinical severity of the disease course.

INTERPRETATION

This study highlights the use of serum C3 as a novel mechanistic biomarker in GBS. Larger prospective studies are needed to validate our findings.

Evidence, detailed characterization and clinical context of complement activation in acute multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a rare, life-threatening complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. MIS-C develops with high fever, marked inflammation and shock-like picture several weeks after exposure to, or mild infection with SARS-CoV-2. Deep immune profiling identified activated macrophages, neutrophils, B-plasmablasts and CD8 + T cells as key determinants of pathogenesis together with multiple inflammatory markers. The disease rapidly responds to intravenous immunoglobulin (IVIG) treatment with clear changes of immune features. Here we present the results of a comprehensive analysis of the complement system in the context of MIS-C activity and describe characteristic changes during IVIG treatment. We show that activation markers of the classical, alternative and terminal pathways are highly elevated, that the activation is largely independent of anti-SARS-CoV-2 humoral immune response, but is strongly associated with markers of macrophage activation. Decrease of complement activation is closely associated with rapid improvement of MIS-C after IVIG treatment.

The role of the complement system in Multiple Sclerosis: A review

The complement system has been involved in the pathogenesis of multiple neuroinflammatory and neurodegenerative conditions. In this review, we evaluated the possible role of complement activation in multiple sclerosis (MS) with a focus in progressive MS, where the disease pathogenesis remains to be fully elucidated and treatment options are limited. The evidence for the involvement of the complement system in the white matter plaques and gray matter lesions of MS stems from immunohistochemical analysis of post-mortem MS brains, in vivo serum and cerebrospinal fluid biomarker studies, and animal models of Experimental Autoimmune Encephalomyelitis (EAE). Complement knock-out studies in these animal models have revealed that this system may have a “double-edge sword” effect in MS. On the one hand, complement proteins may aid in promoting the clearance of myelin degradation products and other debris through myeloid cell-mediated phagocytosis. On the other, its aberrant activation may lead to demyelination at the rim of progressive MS white matter lesions as well as synapse loss in the gray matter. The complement system may also interact with known risk factors of MS, including as Epstein Barr Virus (EBV) infection, and perpetuate the activation of CNS self-reactive B cell populations. With the mounting evidence for the involvement of complement in MS, the development of complement modulating therapies for this condition is appealing. Herein, we also reviewed the pharmacological complement inhibitors that have been tested in MS animal models as well as in clinical trials for other neurologic diseases. The potential use of these agents, such as the C5-binding antibody eculizumab in MS will require a detailed understanding of the role of the different complement effectors in this disease and the development of better CNS delivery strategies for these compounds.

Antibody Therapies in Autoimmune Inflammatory Myopathies: Promising Treatment Options

Inflammatory myopathies, including polymyositis (PM), dermatomyositis (DM), inclusion body myositis (IBM), necrotizing myopathy (NM), antisynthetase syndrome (ASS) and overlap myositis (OM), in short myositis, are rare diseases. All forms of myositis have progressive muscle weakness in common, with each subtype characterized by different autoantibody profiles, histological findings and extramuscular manifestations. Due to better understanding of the pathogenesis of the muscle inflammation in myositis, new molecular pathways for targeted therapy have been discovered. Current therapies aim at different components of the innate or the adaptive immune response. Additionally, non-inflammatory mechanisms in myositis have come into focus as possible treatment targets. The use of therapeutical antibodies in myositis has been examined in various clinical studies, several of them randomized controlled ones: Depletion of B-cells by rituximab has been established as treatment of refractory myositis. IVIG, an antibody therapy in the wider sense, has now been licensed for DM following a recent positive clinical trial. Negative study results were reported in randomized trials with infliximab, sifalimumab and bimagrumab. Studies on basiliximab and eculizumab are currently underway, and are expected to yield results in a couple of years. Despite some promising results of clinical studies with antibody therapy in myositis, further research is crucial to optimize the treatment for this debilitating disease and to find treatment alternatives for treatment-refractory patients.

[The efficacy of eculizumab against post-thymectomy exacerbations in thymoma associated myasthenia gravis (MG)]

We report a 62-year-old woman with thymoma associated myasthenia gravis (MG). She had significant dysphagia and was treated with corticosteroids, intravenous immunoglobulin (IVIG), immunoadsorption plasmapheresis (IAPP), and immunosuppressive drugs, and the extended thymectomy. Her symptoms gradually improved, but 3 weeks after thymectomy, her bulbar symptoms recurred. Although she was treated with repeated IVIG and IAPP, her symptom remained. Finally, after starting eculizumab did her symptoms go into complete remission. This case suggests the efficacy of anti-complement therapy for postoperative exacerbation of MG.

Vaccine-Associated Thrombocytopenia and Thrombosis: Venous Endotheliopathy Leading to Venous Combined Micro-Macrothrombosis

Serious vaccine-associated side effects are very rare. Major complications of vaccines are thrombocytopenia and thrombosis in which pathogenetic mechanism is consistent with endotheliopathy characterized by "attenuated" sepsis-like syndrome, leading to the activation of inflammatory and microthrombotic pathway. In the COVID-19 pandemic, acute respiratory distress syndrome caused by microthrombosis has been the major clinical phenotype from the viral sepsis in association with endotheliopathy-associated vascular microthrombotic disease (EA-VMTD), sometimes presenting with thrombotic thrombocytopenic purpura (TTP)-like syndrome. Often, venous thromboembolism has coexisted due to additional vascular injury. In contrast, clinical phenotypes of vaccine complication have included "silent" immune thrombocytopenic purpura (ITP-like syndrome), multiorgan inflammatory syndrome, and deep venous thrombosis (DVT), cerebral venous sinus thrombosis (CVST) in particular. These findings are consistent with venous (v) EA-VMTD. In vEA-VMTD promoted by activated complement system following vaccination, "consumptive" thrombocytopenia develops as ITP-like syndrome due to activated unusually large von Willebrand factor (ULVWF) path of hemostasis via microthrombogenesis. Thus, the pathologic phenotype of ITP-like syndrome is venous microthrombosis. Myocarditis/pericarditis and other rare cases of inflammatory organ syndrome are promoted by inflammatory cytokines released from activated inflammatory pathway, leading to various organ endotheliitis. Vaccine-associated CVST is a form of venous combined "micro-macrothrombosis" composed of binary components of "microthrombi strings" from vEA-VMTD and "fibrin meshes" from vaccine-unrelated incidental vascular injury perhaps such as unreported head trauma. This mechanism is identified based on "two-path unifying theory" of in vivo hemostasis. Venous combined micro-macrothrombosis due to vaccine is much more serious thrombosis than isolated distal DVT made of macrothrombus. This paradigm changing novel concept of combined micro-macrothrombosis implies the need of combined therapy of a complement inhibitor and anticoagulant for CVST and other complex forms of DVT.

The Dual Role of a Polyvalent IgM/IgA-Enriched Immunoglobulin Preparation in Activating and Inhibiting the Complement System

Activation of the complement system is important for efficient clearance of a wide variety of pathogens via opsonophagocytosis, or by direct lysis via complement-dependent cytotoxicity (CDC). However, in severe infections dysregulation of the complement system contributes to hyperinflammation. The influence of the novel IgM/IgA-enriched immunoglobulin preparation trimodulin on the complement pathway was investigated in in vitro opsonophagocytosis, binding and CDC assays. Immunoglobulin levels before and after trimodulin treatment were placed in relation to complement assessments in humans. In vitro, trimodulin activates complement and induces opsonophagocytosis, but also interacts with opsonins C3b, C4b and anaphylatoxin C5a in a concentration-dependent manner. This was not observed for standard intravenous IgG preparation (IVIg). Accordingly, trimodulin, but not IVIg, inhibited the downstream CDC pathway and target cell lysis. If applied at a similar concentration range in healthy subjects, trimodulin treatment resulted in C3 and C4 consumption in a concentration-dependent manner, which was extended in patients with severe community-acquired pneumonia. Complement consumption is found to be dependent on underlying immunoglobulin levels, particularly IgM, pinpointing their regulative function in humans. IgM/IgA provide a balancing effect on the complement system. Trimodulin may enhance phagocytosis and opsonophagocytosis in patients with severe infections and prevent excessive pathogen lysis and release of harmful anaphylatoxins.

Emerging New Approaches in Desensitization: Targeted Therapies for HLA Sensitization

There is an urgent need for therapeutic interventions for desensitization and antibody-mediated rejection (AMR) in sensitized patients with preformed or de novo donor-specific HLA antibodies (DSA). The risk of AMR and allograft loss in sensitized patients is increased due to preformed DSA detected at time of transplant or the reactivation of HLA memory after transplantation, causing acute and chronic AMR. Alternatively, de novo DSA that develops post-transplant due to inadequate immunosuppression and again may lead to acute and chronic AMR or even allograft loss. Circulating antibody, the final product of the humoral immune response, has been the primary target of desensitization and AMR treatment. However, in many cases these protocols fail to achieve efficient removal of all DSA and long-term outcomes of patients with persistent DSA are far worse when compared to non-sensitized patients. We believe that targeting multiple components of humoral immunity will lead to improved outcomes for such patients. In this review, we will briefly discuss conventional desensitization methods targeting antibody or B cell removal and then present a mechanistically designed desensitization regimen targeting plasma cells and the humoral response.

Antibody Therapy: From Diphtheria to Cancer, COVID-19, and Beyond

The dawn of the 20th century saw the formative years of developments in immunology. In particular, immunochemistry, specifically pertaining to antibodies, was extensively studied. These studies laid the foundations for employing antibodies in a variety of ways. Not surprisingly, antibodies have been used for applications ranging from biomedical research to disease diagnostics and therapeutics to evaluation of immune responses during natural infection and those elicited by vaccines. Despite recent advancements in cellular immunology and the excitement of T cell therapy, use of antibodies represents a large proportion of immunotherapeutic approaches as well as clinical interventions. Polyclonal antibodies in the form of plasma or sera continue to be used to treat a number of diseases, including autoimmune disorders, cancers, and infectious diseases. Historically, antisera to toxins have been the longest serving biotherapeutics. In addition, intravenous immunoglobulins (IVIg) have been extensively used to treat not only immunodeficiency conditions but also autoimmune disorders. Beyond the simplistic suppositions of their action, the IVIg have also unraveled the immune regulatory and homeostatic ramifications of their use. The advent of monoclonal antibodies (MAbs), on the other hand, has provided a clear pathway for their development as drug molecules. MAbs have found a clear place in the treatment of cancers and extending lives and have been used in a variety of other conditions. In this review, we capture the important developments in the therapeutic applications of antibodies to alleviate disease, with a focus on some of the recent developments.

Complement in neurological disorders and emerging complement-targeted therapeutics

The complement system consists of a network of plasma and membrane proteins that modulate tissue homeostasis and contribute to immune surveillance by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement components contribute to the pathogenesis of some autoimmune neurological disorders and could even contribute to neurodegenerative diseases. In this Review, we summarize current knowledge about the main functions of the complement pathways and the involvement of complement in neurological disorders. We describe the complex network of complement proteins that target muscle, the neuromuscular junction, peripheral nerves, the spinal cord or the brain and discuss the autoimmune mechanisms of complement-mediated myopathies, myasthenia, peripheral neuropathies, neuromyelitis and other CNS disorders. We also consider the emerging role of complement in some neurodegenerative diseases, such as Alzheimer disease, amyotrophic lateral sclerosis and even schizophrenia. Finally, we provide an overview of the latest complement-targeted immunotherapies including monoclonal antibodies, fusion proteins and peptidomimetics that have been approved, that are undergoing phase I–III clinical trials or that show promise for the treatment of neurological conditions that respond poorly to existing immunotherapies.

In this Review, Dalakas et al. discuss the complement system, the role it plays in autoimmune neurological disease and neurodegenerative disease, and provide an overview of the latest therapeutics that target complement and that can be used for or have potential in neurological disorders.

Complement has an important physiological role in host immune defences and tissue remodelling.

The physiological role of complement extends to the regulation of synaptic development.

Complement has a key pathophysiological role in autoimmune neurological diseases and mediates the actions of pathogenic autoantibodies, such as acetylcholine receptor antibodies and aquaporin 4 antibodies.

For some autoimmune neurological diseases, such as myasthenia gravis and neuromyelitis optica spectrum disorders, approved complement-targeted treatments are now available.

Complement also seems to be of pathogenic relevance in neurodegenerative diseases such as Alzheimer disease, in which innate immune-driven inflammation is receiving increasing attention.

The field of complement-targeted therapeutics is rapidly expanding, with several FDA-approved agents and others currently in phase II and phase III clinical trials.

COVID-19: A collision of complement, coagulation and inflammatory pathways

COVID-19 is frequently accompanied by a hypercoagulable inflammatory state with microangiopathic pulmonary changes that can precede the diffuse alveolar damage characteristic of typical acute respiratory distress syndrome (ARDS) seen in other severe pathogenic infections. Parallels with systemic inflammatory disorders such as atypical hemolytic uremic syndrome (aHUS) have implicated the complement pathway in the pathogenesis of COVID-19, and particularly the anaphylatoxins C3a and C5a released from cleavage of C3 and C5, respectively. C5a is a potent cell signalling protein that activates a cytokine storm-a hyper-inflammatory phenomenon-within hours of infection and the innate immune response. However, excess C5a can result in a pro-inflammatory environment orchestrated through a plethora of mechanisms that propagate lung injury, lymphocyte exhaustion, and an immune paresis. Furthermore, disruption of the homeostatic interactions between complement and extrinsic and intrinsic coagulation pathways contributes to a net pro-coagulant state in the microvasculature of critical organs. Fatal COVID-19 has been associated with a systemic inflammatory response accompanied by a pro-coagulant state and organ damage, particularly microvascular thrombi in the lungs and kidneys. Pathologic studies report strong evidence of complement activation. C5 blockade reduces inflammatory cytokines and their manifestations in animal studies, and has shown benefits in patients with aHUS, prompting investigation of this approach in the treatment of COVID-19. This review describes the role of the complement pathway and particularly C5a and its aberrations in highly pathogenic virus infections, and therefore its potential as a therapeutic target in COVID-19.

High-Dose Intravenous Immunoglobulins in the Treatment of Severe Acute Viral Pneumonia: The Known Mechanisms and Clinical Effects

The current outbreak of viral pneumonia, caused by novel coronavirus SARS-CoV-2, is the focus of worldwide attention. The WHO declared the COVID-19 outbreak a pandemic event on Mar 12, 2020, and the number of confirmed cases is still on the rise worldwide. While most infected individuals only experience mild symptoms or may even be asymptomatic, some patients rapidly progress to severe acute respiratory failure with substantial mortality, making it imperative to develop an efficient treatment for severe SARS-CoV-2 pneumonia alongside supportive care. So far, the optimal treatment strategy for severe COVID-19 remains unknown. Intravenous immunoglobulin (IVIg) is a blood product pooled from healthy donors with high concentrations of immunoglobulin G (IgG) and has been used in patients with autoimmune and inflammatory diseases for more than 30 years. In this review, we aim to highlight the known mechanisms of immunomodulatory effects of high-dose IVIg therapy, the immunopathological hypothesis of viral pneumonia, and the clinical evidence of IVIg therapy in viral pneumonia. We then make cautious therapeutic inferences about high-dose IVIg therapy in treating severe COVID-19. These inferences may provide relevant and useful insights in order to aid treatment for COVID-19.

Content of anti-β-amyloid42 oligomers antibodies in multiple batches from different immunoglobulin preparations

Immunoglobulin preparations are one of the promising drugs for Alzheimer's disease (AD). Anti-β-amyloid (Aβ) oligomers antibodies in immunoglobulin preparations are considered to be critical for the therapeutic effect against Alzheimer's disease. However, the antibodies content in immunoglobulin preparations varies greatly. In order to determine which factor contributes to the difference of the antibodies content, the content of anti-Aβ oligomers antibodies in multiple batches of immunoglobulin preparations from two manufacturers were measured by enzyme-linked immunosorbent assay. The results showed that no significant difference was found in the antibodies content among different bathes of normal immunoglobulin preparations prepared by the same process from the same manufacturer, whereas significant difference was found in the antibodies content between normal immunoglobulin preparations prepared by ethanol fractionation and those by chromatography process from the same manufacturer. In addition, significant variation existed in the antibodies content between normal immunoglobulin preparations and specific immunoglobulin preparations that are produced by plasma pool of immunized donors. Based on analysis of these results, the preparation process and raw plasma could be the main contributing factors affecting the content of anti-Aβ oligomers antibodies in immunoglobulin preparations. This finding might help to develop AD-specific immunoglobulin preparation containing higher content of anti-Aβ oligomers antibodies.

Intravenous immunoglobulin mediates anti-inflammatory effects in peripheral blood mononuclear cells by inducing autophagy

Autophagy plays an important role in the regulation of autoimmune and autoinflammatory responses of the immune cells. Defective autophagy process is associated with various autoimmune and inflammatory diseases. Moreover, in many of these diseases, the therapeutic use of normal immunoglobulin G or intravenous immunoglobulin (IVIG), a pooled normal IgG preparation, is well documented. Therefore, we explored if IVIG immunotherapy exerts therapeutic benefits via induction of autophagy in the immune cells. Here we show that IVIG induces autophagy in peripheral blood mononuclear cells (PBMCs). Further dissection of this process revealed that IVIG-induced autophagy is restricted to inflammatory cells like monocytes, dendritic cells, and M1 macrophages but not in cells associated with Th2 immune response like M2 macrophages. IVIG induces autophagy by activating AMP-dependent protein kinase, beclin-1, class III phosphoinositide 3-kinase and p38 mitogen-activated protein kinase and by inhibiting mammalian target of rapamycin. Mechanistically, IVIG-induced autophagy is F(ab')₂-dependent but sialylation independent, and requires endocytosis of IgG by innate cells. Inhibition of autophagy compromised the ability of IVIG to suppress the inflammatory cytokines in innate immune cells. Moreover, IVIG therapy in inflammatory myopathies such as dermatomyositis, antisynthetase syndrome and immune-mediated necrotizing myopathy induced autophagy in PBMCs and reduced inflammatory cytokines in the circulation, thus validating the translational importance of these results. Our data provide insight on how circulating normal immunoglobulins maintain immune homeostasis and explain in part the mechanism by which IVIG therapy benefits patients with autoimmune and inflammatory diseases.

Haemophagocytic lymphohisticytosis-an underrecognized hyperinflammatory syndrome

Haemophagocytic lymphohisticytosis (HLH) is a syndrome of uncontrolled, severe systemic inflammation (hyperinflammation) arising either from a genetic immune system defect [primary (pHLH)] or triggered as a complication of malignancy, infection, or rheumatologic disease [secondary (sHLH)]. Patients with HLH often have non-specific symptoms and become progressively and critically unwell, with fever, cytopenia and multi-organ failure. Untreated, HLH is almost universally fatal, but even when treated, mortality is high, particularly when HLH complicates malignancy. HLH is managed with immunosuppression, and this can seem difficult to justify in such unwell patients. This review aims to examine the diagnostic and treatment challenges posed by sHLH and to improve recognition among rheumatologists who, being expert in the management of multisystem diseases and in the use of immunosuppression, are ideally placed to deliver care and build an evidence base for better disease characterization and treatment.

Role of complement and potential of complement inhibitors in myasthenia gravis and neuromyelitis optica spectrum disorders: a brief review

The complement system is a powerful member of the innate immune system. It is highly adept at protecting against pathogens, but exists in a delicate balance between its protective functions and overactivity, which can result in autoimmune disease. A cascade of complement proteins that requires sequential activation, and numerous complement regulators, exists to regulate a proportionate response to pathogens. In spite of these mechanisms there is significant evidence for involvement of the complement system in driving the pathogenesis of variety of diseases including neuromyelitis optica spectrum disorders (NMOSD) and myasthenia gravis (MG). As an amplification cascade, there are an abundance of molecular targets that could be utilized for therapeutic intervention. Clinical trials assessing complement pathway inhibition in both these conditions have recently been completed and include the first randomized placebo-controlled trial in NMOSD showing positive results. This review aims to review and update the reader on the complement system and the evolution of complement-based therapeutics in these two disorders.

Targeted Therapies for Autoimmune Bullous Diseases: Current Status

Autoimmune bullous skin disorders are rare but meaningful chronic inflammatory diseases, many of which had a poor or devastating prognosis prior to the advent of immunosuppressive drugs such as systemic corticosteroids, which down-regulate the immune pathogenesis in these disorders. Glucocorticoids and adjuvant immunosuppressive drugs have been of major benefit for the fast control of most of these disorders, but their long-term use is limited by major side effects such as blood cytopenia, osteoporosis, diabetes mellitus, hypertension, and gastrointestinal ulcers. In recent years, major efforts were made to identify key elements in the pathogenesis of autoimmune bullous disorders, leading to the identification of their autoantigens, which are mainly located in desmosomes (pemphigus) and the basement membrane zone (pemphigoids). In the majority of cases, immunoglobulin G, and to a lesser extent, immunoglobulin A autoantibodies directed against distinct cutaneous adhesion molecules are directly responsible for the loss of cell-cell and cell-basement membrane adhesion, which is clinically related to the formation of blisters and/or erosions of the skin and mucous membranes. We describe and discuss novel therapeutic strategies that directly interfere with the production and regulation of pathogenic autoantibodies (rituximab), their catabolism (intravenous immunoglobulins), and their presence in the circulation and extravascular tissues such as the skin (immunoadsorption), leading to a significant amelioration of disease. Moreover, we show that these novel therapies have pleiotropic effects on various proinflammatory cells and cytokines. Recent studies in bullous pemphigoid suggest that targeting of immunoglobulin E autoantibodies (omalizumab) may be also beneficial. In summary, the introduction of targeted therapies in pemphigus and pemphigoid holds major promise because of the high efficacy and fewer side effects compared with conventional global immunosuppressive therapy.

A recombinant human IgG1 Fc multimer designed to mimic the active fraction of IVIG in autoimmunity

The antiinflammatory effects of i.v. Ig (IVIG) in the treatment of autoimmune disease are due, in part, to the Fc fragments of Ig aggregates. In order to capitalize on the known antiinflammatory and tolerogenic properties of Ig Fc aggregates, we created a recombinant human IgG1 Fc multimer, GL-2045. In vitro, GL-2045 demonstrated high-avidity binding to Fc receptors, blocked the binding of circulating immune complexes from patients with rheumatoid arthritis to human Fcγ receptors (FcγRs), and inhibited antibody-mediated phagocytosis at log order-lower concentrations than IVIG. In vivo, administration of GL-2045 conferred partial protection against antibody-mediated platelet loss in a murine immune thrombocytopenic purpura (ITP) model. GL-2045 also suppressed disease activity in a therapeutic model of murine collagen-induced arthritis (CIA), which was associated with reduced circulating levels of IL-6. Furthermore, GL-2045 administration to nonhuman primates (NHPs) transiently increased systemic levels of the antiinflammatory cytokines IL-10 and IL-1RA, reduced the proinflammatory cytokine IL-8, and decreased surface expression of CD14 and HLA-DR on monocytes. These findings demonstrate the immunomodulatory properties of GL-2045 and suggest that it has potential as a treatment for autoimmune and inflammatory diseases, as a recombinant alternative to IVIG.

IVIG-mediated effector functions in autoimmune and inflammatory diseases

Intravenous immunoglobulin (IVIG) is a pooled preparation of normal IgG obtained from several thousand healthy donors. It is widely used in the immunotherapy of a large number of autoimmune and inflammatory diseases. The mechanisms of action of IVIG are complex and, as discussed in this review, experimental and clinical data provide an indicator that the therapeutic benefit of IVIG therapy is due to several mutually non-exclusive mechanisms affecting soluble mediators as well as cellular components of the immune system. These mechanisms depend on Fc and/or F(ab')2 fragments. A better understanding of the effector functions of IVIG should help in identification of biomarkers of responses to IVIG in autoimmune patients.

Myasthenia gravis: the role of complement at the neuromuscular junction

Generalized myasthenia gravis (gMG) is a rare autoimmune disorder characterized by skeletal muscle weakness caused by disrupted neurotransmission at the neuromuscular junction (NMJ). Approximately 74-88% of patients with gMG have acetylcholine receptor (AChR) autoantibodies. Complement plays an important role in innate and antibody-mediated immunity, and activation and amplification of complement results in the formation of membrane attack complexes (MACs), lipophilic proteins that damage cell membranes. The role of complement in gMG has been demonstrated in animal models and patients. Studies in animals lacking specific complement proteins have confirmed that MAC formation is required to induce experimental autoimmune MG (EAMG) and NMJ damage. Complement inhibition in EAMG models can prevent disease induction and reverse its progression. Patients with anti-AChR⁺ MG have autoantibodies and MACs present at NMJs. Damaged NMJs are associated with more severe disease, fewer AChRs, and MACs in synaptic debris. Current MG therapies do not target complement directly. Eculizumab is a humanized monoclonal antibody that inhibits cleavage of complement protein C5, preventing MAC formation. Eculizumab treatment improved symptoms compared with placebo in a phase II study in patients with refractory gMG. Direct complement inhibition could preserve NMJ physiology and muscle function in patients with anti-AChR⁺ gMG.

[Therapeutic administration of immunoglobulins]

BACKGROUND

Intravenously administered immunoglobulins have multiple modes of action that are anti-inflammatory. They can therefore be beneficial in a number of autoimmune disorders.

OBJECTIVE

The aim of this article is to analyze and summarize studies on the administration of intravenous immunoglobulins in rheumatological diseases.

METHODS

A selective search and analysis of the literature was carried out related to the mode of action and efficacy of intravenous immunoglobulins in rheumatological diseases.

RESULTS AND CONCLUSION

Intravenous immunoglobulins have a broad mode of action and can therefore be beneficial in almost all autoimmune diseases. Conditions in which they are of special benefit include immunothrombopenia (ITP), Kawasaki disease and idiopathic inflammatory myopathies. In rare situations, they may also be indicated in systemic lupus erythematosus (SLE), Sjögren's syndrome and neuropathies, catastrophic antiphospholipid syndrome (APS), scleroderma, antineutrophil cytoplasmic antibody (ANCA) associated vasculitis, pyoderma gangrenosum and scleromyxedema. Severe adverse events are rare. In view of the high costs of the therapy, intravenous immunoglobulins are mostly applied in emergency situations, as salvage therapy when other standard therapies have failed or when severe infections are a contraindication to the administration of immunosuppressants.

A fully recombinant human IgG1 Fc multimer (GL-2045) inhibits complement-mediated cytotoxicity and induces iC3b

GL-2045 is a recombinant human immunoglobulin G1 (IgG1)-based Fc multimer designed to recapitulate the anti-inflammatory activities of intravenous immunoglobulin (IVIG) on the innate and adaptive immune responses. We used functional in vitro studies to determine if GL-2045 could mimic the modulatory activity of IVIG on complement activation. GL-2045, at log-order lower concentrations than heat-aggregated IgG (HAGG) and IVIG, protected antibody-opsonized cells from complement-dependent cytotoxicity. These protective effects were completely mediated by the higher order multimer fractions of GL-2045 and were partially dependent upon sequestration of C1q. Exposure of serum to GL-2045 and, to a lesser extent, IVIG, resulted in high levels of C4a, limited levels of C3a, and no C5a. In contrast, HAGG induced high levels of C4a, C3a, and C5a. The means by which GL-2045 governed complement activation was dependent on its ability to augment the function of factor H, alone and in combination with factor I, to indirectly limit the alternative form of C3 convertase, with resultant increases in the anti-inflammatory molecule, the "inactive" form of C3b, called iC3b. Although IVIG, like GL-2045, potentiated factor H function, it also directly inhibited the alternative form of C3 convertase. Our findings help elucidate how IVIG, GL-2045, and HAGG regulate complement function. Furthermore, the capacity of GL-2045 to sequester C1q and augment factor H activity, in combination with its ability to generate activation-induced immunomodulatory complement split products, such as iC3b, make it a viable drug candidate for the treatment of diverse complement-mediated diseases.

Therapeutic complement inhibition: a promising approach for treatment of neuroimmunological diseases

INTRODUCTION

Autoimmunity is an important cause of disease both in the central and peripheral nervous systems. Aetiologies and clinical manifestations are complex and heterogeneous. Inappropriate control of complement activation at inappropriate sites has been recognized as a major determinant in several neurological conditions, including Guillain-Barré syndrome and neuromyelitis optica. In each case pathogenesis is thought to be associated with generation of autoantibodies which upon binding guide activation of the complement system to self-tissue. Areas covered: Modulation of the complement system activation at such sites may represent a novel therapeutic approach for treatment of immune-mediated inflammatory conditions. In this review we focus on the therapeutic effects of complement inhibitors in Guillain-Barré syndrome and neuromyelitis optica and highlight recent developments within the field. Expert Commentary: Conventional first line treatment strategies in GBS and NMO have the potential disadvantage of causing widespread immunosuppressive effects. A more targeted approach may therefore be more effective and less disruptive to the immune system, especially in the case of NMO, which requires long term immunosuppression. Modulation of the complement system may hold the key and has already been shown to be of clinical benefit in other non-neurological conditions, including paroxysmal nocturnal hemoglobinuria and hereditary angioedema.

Dose-dependent inhibition of demyelination and microglia activation by IVIG

Objective

Intravenous immunoglobulin (IVIG) is an established treatment for numerous autoimmune conditions. Clinical trials of IVIG for multiple sclerosis, using diverse dose regimens, yielded controversial results. The aim of this study is to dissect IVIG effector mechanisms on demyelination in an ex vivo model of the central nervous system (CNS)‐immune interface.

Methods

Using organotypic cerebellar slice cultures (OSC) from transgenic mice expressing green fluorescent protein (GFP) in oligodendrocytes/myelin, we induced extensive immune‐mediated demyelination and oligodendrocyte loss with an antibody specific for myelin oligodendrocyte glycoprotein (MOG) and complement. Protective IVIG effects were assessed by live imaging of GFP expression, confocal microscopy, immunohistochemistry, gene expression analysis and flow cytometry.

Results

IVIG protected OSC from demyelination in a dose‐dependent manner, which was at least partly attributed to interference with complement‐mediated oligodendroglia damage, while binding of the anti‐MOG antibody was not prevented. Staining with anti‐CD68 antibodies and flow cytometry confirmed that IVIG prevented microglia activation and oligodendrocyte death, respectively. Equimolar IVIG‐derived Fab fragments or monoclonal IgG did not protect OSC, while Fc fragments derived from a polyclonal mixture of human IgG were at least as potent as intact IVIG.

Interpretation

Both intact IVIG and Fc fragments exert a dose‐dependent protective effect on antibody‐mediated CNS demyelination and microglia activation by interfering with the complement cascade and, presumably, interacting with local immune cells. Although this experimental model lacks blood–brain barrier and peripheral immune components, our findings warrant further studies on optimal dose finding and alternative modes of application to enhance local IVIG concentrations at the site of tissue damage.

Intravenous Immunoglobulins: Mode of Action and Indications in Autoimmune and Inflammatory Dermatoses

Intravenous immunoglobulins (IVIGs), a mixture of variable amounts of proteins (albumin, IgG, IgM, IgA, and IgE antibodies), as well as salt, sugar, solvents, and detergents, are successfully used to treat a variety of dermatological disorders. For decades, IVIGs have been administered for treatment of infectious diseases and immune deficiencies, since they contain natural antibodies that represent a first-line defense against pathogens. Today their indication has expanded, including the off-label therapy for a variety of autoimmune and inflammatory diseases. In dermatology, IVIGs are administered for treatment of different disorders at different therapeutic regimens, mostly with higher doses then those administered for treatment of infectious diseases. The aim of this prospective review is to highlight the indications, effectiveness, side effects, and perspectives of the systemic treatment with IVIGs for patients with severe, life-threatening, and resistant to conventional therapies autoimmune or inflammatory dermatoses.

Complement activity is associated with disease severity in multifocal motor neuropathy

Objective:

To investigate whether high innate activity of the classical and lectin pathways of complement is associated with multifocal motor neuropathy (MMN) and whether levels of innate complement activity or the potential of anti-GM1 antibodies to activate the complement system correlate with disease severity.

Methods:

We performed a case-control study including 79 patients with MMN and 79 matched healthy controls. Muscle weakness was documented with Medical Research Council scale sum score and axonal loss with nerve conduction studies. Activity of the classical and lectin pathways of complement was assessed by ELISA. We also determined serum mannose-binding lectin (MBL) concentrations and polymorphisms in the MBL gene (MBL2) and quantified complement-activating properties of anti-GM1 IgM antibodies by ELISA.

Results:

Activity of the classical and lectin pathways, MBL2 genotypes, and serum MBL concentrations did not differ between patients and controls. Complement activation by anti-GM1 IgM antibodies was exclusively mediated through the classical pathway and correlated with antibody titers (p < 0.001). Logistic regression analysis showed that both high innate activity of the classical pathway of complement and high complement-activating capacity of anti-GM1 IgM antibodies were significantly associated with more severe muscle weakness and axonal loss.

Conclusion:

High innate activity of the classical pathway of complement and efficient complement-activating properties of anti-GM1 IgM antibodies are determinants of disease severity in patients with MMN. These findings underline the importance of anti-GM1 antibody–mediated complement activation in the pathogenesis and clinical course of MMN.

Contributions of T lymphocyte abnormalities to therapeutic outcomes in newly diagnosed patients with immune thrombocytopenia

T cell abnormalities have been reported to play an important role in pathogenesis of immune thrombocytopenia (ITP) besides specific autoantibodies towards platelet. The aim of this study was to explore the clinical importance of T lymphocyte subsets in adult patients with newly diagnosed ITP before and after first-line treatment. Elderly ITP patients were also studied and we tried to analyze the relationships between these items and therapeutic outcomes. The patients were treated with intravenous immunoglobulin (IVIG) plus corticosteroids and therapeutic responses were evaluated. As a result, compared with the controls, absolute lymphocyte counts in ITP patients decreased significantly before treatment. After treatment, lymphocyte counts restored to control level regardless of their treatment outcomes. In addition, we observed increased IgG and CD19+ cell expression and decreased CD4+/CD8+ cell ratio in both whole ITP group and elderly group before treatment. After treatment, the increased IgG and CD19+ cell expression could be reduced in both respond and non-respond group regardless of patient age, while CD4+/CD8+ cell ratio could not be corrected in non-respond ITP patients. In non-respond ITP patients, increased CD8+ cell expression was noticed and could not be corrected by first-line treatment. Furthermore, even lower NK cell expression was found in non-respond elderly patients after treatment when compared with that in controls. Our findings suggest that ITP patients usually had less numbers of peripheral lymphocytes and patients with higher levels of CD8+ cells or lower levels of CD4+/CD8+ cell ratio were less likely to respond to first-line treatment. Lower levels of NK cells made therapies in elderly ITP patients even more difficult.

Interference of therapeutic antibodies used in desensitization protocols on lymphocytotoxicity crossmatch results

BACKGROUND

Therapeutic antibodies used to desensitize patients awaiting a human leukocyte antigen (HLA) or ABO-mismatched graft are suspected to interfere with the lymphocytotoxicity crossmatch (LCT-XM) test when they are present in the tested sera because of their potential ability to activate or inhibit the complement.

METHODS

The most frequent therapeutic antibodies (Abs) used in desensitization protocols (intravenous immunoglobulins, rituximab, basiliximab, eculizumab, antithymocyte globulin) were added to a negative- or a positive-control serum at various concentrations, and tested in vitro in a LCT-XM test.

RESULTS

Rituximab turned the LCT-XM positive on B cells at 0.2 μg/mL and antithymocyte globulin turned the LCT-XM positive with T and B cells at 20 μg/mL and 200 μg/mL, respectively. Treatment with dithiothreitol sera, supplemented with rituximab (0.2 and 2 μg/mL) and antithymocyte globulins (20 and 200 μg/mL), partially or totally reduced this positive interference. Intravenous immunoglobulin, eculizumab, and basiliximab did not trigger any interference with the negative control serum. In a positive LCT-XM, eculizumab did not annihilate activation of the rabbit complement. Intravenous immunoglobulins (25 g/L) could partially or totally reduced lysis score of positive crossmatch with weak lysis scores.

CONCLUSION

If eculizumab within the serum did not annihilate rabbit complement activation and basiliximab did not interfere with the crossmatch reaction, treatments based on rituximab, antithymocyte globulin and intravenous immunoglobulins need to be taken into account when interpreting a positive or negative crossmatch test.

On the dark side of therapies with immunoglobulin concentrates: the adverse events

Therapy by human immunoglobulin G (IgG) concentrates is a success story ongoing for decades with an ever increasing demand for this plasma product. The success of IgG concentrates on a clinical level is documented by the slowly increasing number of registered indication and the more rapid increase of the off-label uses, a topic dealt with in another contribution to this special issue of Frontiers in Immunology. A part of the success is the adverse event (AE) profile of IgG concentrates which is, even at life-long need for therapy, excellent. Transmission of pathogens in the last decade could be entirely controlled through the antecedent introduction by authorities of a regulatory network and installing quality standards by the plasma fractionation industry. The cornerstone of the regulatory network is current good manufacturing practice. Non-infectious AEs occur rarely and mainly are mild to moderate. However, in recent times, the increase in frequency of hemolytic and thrombotic AEs raised worrying questions on the possible background for these AEs. Below, we review elements of non-infectious AEs, and particularly focus on hemolysis and thrombosis. We discuss how the introduction of plasma fractionation by ion-exchange chromatography and polishing by immunoaffinity chromatographic steps might alter repertoire of specificities and influence AE profiles and efficacy of IgG concentrates.

Should development of Alzheimer's disease-specific intravenous immunoglobulin be considered?

Recent phase II and III studies with intravenous immunoglobulin (IVIG) in patients with Alzheimer's disease (AD) did not find evidence for the slowing of AD progression compared to placebo-treated patients, in contrast to encouraging results in pilot studies. An additional phase III trial is ongoing. If negative results are found, then further AD studies with IVIG are unlikely unless a manufacturer opts for a trial with high-dose IVIG, which would increase its anti-inflammatory effects but also the risk for adverse events. An alternative approach could be an AD-specific IVIG, supplementing IVIG with higher concentrations of selected antibodies purified from it or produced via recombinant polyclonal antibody technology. These antibodies could include those to amyloid-beta (Aβ, tau protein, inflammatory cytokines, complement activation proteins, and the receptor for advanced glycation end products. IgG fragment crystallizable (Fc) fragments containing terminal sialic acid could be added to increase anti-inflammatory effects. While this product might be more effective in slowing AD clinical progression than current IVIG, there are difficulties with this approach. Preclinical studies would be required to determine which of the antibodies of interest for supplementing current IVIG (for example, antibodies to phosphorylated or oligomeric tau) are actually present (and, therefore, available for purification) in IVIG, and the effects of the product in mouse models of AD. An Investigational New Drug application for an AD-specific IVIG would require United States Food and Drug Administration approval. If the drug would be found to benefit AD patients, meeting the increased demand for IVIG would be challenging.

S100A8-S100A9 protein complex mediates psoriasis by regulating the expression of complement factor C3

Psoriasis is a common heterogeneous inflammatory skin disease with a complex pathophysiology and limited treatment options. Here we performed proteomic analyses of human psoriatic epidermis and found S100A8-S100A9, also called calprotectin, as the most upregulated proteins, followed by the complement component C3. Both S100A8-S100A9 and C3 are specifically expressed in lesional psoriatic skin. S100A9 is shown here to function as a chromatin component modulating C3 expression in mouse and human cells by binding to a region upstream of the C3 start site. When S100A9 was genetically deleted in mouse models of skin inflammation, the psoriasis-like skin disease and inflammation were strongly attenuated, with a mild immune infiltrate and decreased amounts of C3. In addition, inhibition of C3 in the mouse model strongly reduced the inflammatory skin disease. Thus, S100A8-S100A9 can regulate C3 at the nuclear level and present potential new therapeutic targets for psoriasis.

Treatment update of sensitized pediatric kidney transplant recipients: a review

Sensitization of recipients is an increasing problem in children. Some case series in children exist comparing the diverse desensitizing protocols. These protocols include intravenous immunoglobulin, cytomegalovirus immune globulin, plasmapheresis, and some adjunctive therapies such as rituximab. Desensitizing protocols have advantages and disadvantages. Clinical trials are required to determine suitable protocols for sensitized pediatric recipients. We performed a systematic review of these protocols in children. A massive search was done in PubMed, Embase, and the Cochrane library system. The results of these studies are compared.

Dense deposit disease in Korean children: a multicenter clinicopathologic study

The purpose of this study was to investigate the clinical, laboratory, and pathologic characteristics of dense deposit disease (DDD) in Korean children and to determine whether these characteristics differ between Korean and American children with DDD. In 2010, we sent a structured protocol about DDD to pediatric nephrologists throughout Korea. The data collected were compared with previously published data on 14 American children with DDD. Korean children had lower 24-hr urine protein excretion and higher serum albumin levels than American children. The light microscopic findings revealed that a higher percentage of Korean children had membranoproliferative glomerulonephritis patterns (Korean, 77.8%; American, 28.6%, P = 0.036), whereas a higher percentage of American children had crescents (Korean, 0%; American, 78.6%, P < 0.001). The findings from the electron microscopy revealed that Korean children were more likely to have segmental electron dense deposits in the lamina densa of the glomerular basement membrane (Korean, 100%; American, 28.6%, P = 0.002); mesangial deposit was more frequent in American children (Korean, 66.7%; American, 100%, P = 0.047). The histological findings revealed that Korean children with DDD were more likely to show membranoproliferative glomerulonephritis patterns than American children. The degree of proteinuria and hypoalbuminemia was milder in Korean children than American children.

Intravenous immunoglobulin in the management of lupus nephritis

The occurrence of nephritis in patients with systemic lupus erythematosus is associated with increased morbidity and mortality. The pathogenesis of lupus nephritis is complex, involving innate and adaptive cellular and humoral immune responses. Autoantibodies in particular have been shown to be critical in the initiation and progression of renal injury, via interactions with both Fc-receptors and complement. One approach in the management of patients with lupus nephritis has been the use of intravenous immunoglobulin. This therapy has shown benefit in the setting of many forms of autoantibody-mediated injury; however, the mechanisms of efficacy are not fully understood. In this paper, the data supporting the use of immunoglobulin therapy in lupus nephritis will be evaluated. In addition, the potential mechanisms of action will be discussed with respect to the known involvement of complement and Fc-receptors in the kidney parenchyma. Results are provocative and warrant additional clinical trials.

Cardiac antibody-mediated rejection

Many factors limit short- and long-term survival after pediatric heart transplantation. Historically, attention had been directed toward T-cell responses and acute cellular rejection. Presence of pretransplant antibodies against HLA is associated with increased donor wait times and poor post-transplant outcomes. Therapies aimed to mitigate circulating antibodies include plasmapheresis, protein A immunoadsorption columns, intravenous immune globulin, rituximab, and bortezomib. The negative effects of B cells, HLA antibodies, and AMR and potential interventions are the focus of this review article.

Antifibrosis: to reverse the irreversible

Fibrosis is a pathological process that includes scar formation and overproduction of extracellular matrix by the connective tissue as a response to tissue damage. The fibrotic process involves multiple organs and results in progressive life-threatening diseases. Today, we know more about the molecular mechanism that leads to fibrosis involving different type of cells, cytokines, chemokines, and tissue enzymes. Fibrosis was considered an irreversible process, at least clinically, and is still usually treated by anti-inflammatory and immunosuppressive agents. No proven antifibrotic therapy has shown efficacy in ameliorating the clinical course of fibrotic diseases, but our current understanding led to the development of different drugs with promising results, like: mycophenolate mofetil, interferon, relaxin, and intravenous immunoglobulin. This review will provide a glance to this heavily investigated subject.

Natural antibodies and complement modulate intimal thickening after arterial injury

Immune factors are involved in modulating neointimal response to arterial wall injury, but the role of individual immune effectors in this response remains unclear. Using a carotid cuff injury model in mice, we tested the role of immunoglobulin isotypes in modulating intimal thickening by using adoptive transfer of splenocytes from WT mice, or the direct administration of IgG or IgM into immune-deficient Rag-1-/- [Rag-1 knockout (Rag-1KO)] mice. The direct role of complement was also tested by depletion of complement. Splenocytes from WT mice were isolated and adoptively transferred to Rag-1KO mice subjected to carotid cuff arterial injury. Transfer of splenocytes to Rag-1KO mice resulted in increased serum IgM and IgG within 48 h and were comparable to WT levels by 21 days after injury. Splenocyte transfer in Rag-1KO decreased intimal area by 40% compared with Rag-1KO mice without cell transfer. To further differentiate the relative contribution of IgM or IgG in reducing intimal thickening, additional groups of Rag-1KO mice were subjected to injury and given intravenous injections of pooled mouse IgG or IgM. Both IgG and IgM treatment significantly reduced intimal thickening compared with untreated Rag-1KO mice. Immunoglobulin treatments modified serum complement C3 profile and decreased C3 presence in injured arteries. Depletion of C3 using cobra venom factor in Rag-1KO mice significantly decreased intimal thickening. Our results identify the direct role of natural IgG and IgM, and complement in the modulation of neointimal response to arterial injury.

Intravenous immunoglobulins induce potentially synergistic immunomodulations in autoimmune disorders

The increase in platelets in patients with immune thrombocytopenia (ITP) by intravenous administration of human immunoglobulin concentrates (IVIG) reflects a therapeutic immunomodulatory intervention targeted at the disturbed immune response in many inflammatory and autoimmune disorders. These immunoglobulin concentrates contain large numbers of antibodies as well as trace levels of various other immunologically active molecules. Clinical and laboratory studies have documented various mechanisms of action of IVIG. The complex network of immunological reactions resulting from the infusion of IVIG includes changes in several cytokines, interactions with dendritic cells, T- and B- lymphocyte effects, macrophage effects, mediated by distinct Fc-gamma receptors. In addition, effects on complement components and apoptosis have also been observed. Synergism between the different elements of the immune response characterizes the beneficial effects of IVIG in inflammatory and autoimmune disorders. They have immunopathogeneses and clinical manifestations which are difficult to define and therefore IVIG treatment indications remain heterogeneous. Dose finding studies are missing for most of the indications of the drug. In future research, defining the appropriate subgroups of patients should be undertaken. This may be accomplished by prospective registries collecting data on large numbers of patients with long-term follow-up. Controlled clinical and laboratory studies may follow based on new, validated patient selection criteria and focused on mechanisms of action, leading to more evidence-based indications.