Epileptic syndrome in systemic lupus erythematosus and neuronal autoantibody associations.

We investigated systemic lupus erythematosus (SLE) patients with epilepsy, a major and organic neurological symptom. Our aim was to test patients for the autoimmune epilepsy-associated antibodies anti-GAD, anti-NMDAR, anti-AMPAR1/2, anti-GABABR and anti-VGKC. We tested sera from ten SLE patients with current or previous episodes of epileptic seizures. In addition, sera were tested for staining on primary hippocampal neurons. The patients' clinical and neuroimaging profile, disease activity and accumulated damage scores and therapeutic regimens administered were recorded, and correlations were evaluated. Patients were negative for all anti-neuronal autoantibodies tested, and showed no staining on primary hippocampal cells, which suggests the absence of autoantibodies against neuronal cell surface antigens. Epileptic seizures were all tonic-clonic, and all patients had high disease activity (mean SLE Damage Acticity Index score 19.3 ± 7.3). Six patients had minor or no brain magnetic resonance imaging findings, and three had major findings. 9/10 patients received immunosuppression for 5 ± 4 months, while anti-convulsive treatment was administered to all patients (4.2 ± 3 years). Our results suggest that the majority of SLE-related epileptic seizures cannot be attributed to the action of a single antibody against neuronal antigens. Studies with larger neuropsychiatric SLE populations and stricter inclusion criteria are necessary to verify these findings.

7th International Immunoglobulin Conference: Interlaken Leadership Awards.

The Interlaken Leadership Awards (ILAs), established in 2010, are monetary grants pledged annually by CSL Behring to fund research into the use of immunoglobulin (Ig) therapy, especially into its use in neurological disorders. Five recipients of the 2011/2012 Awards were invited to present their research at the 7th International Immunoglobulin Conference. Dr Honnorat reports on paraneoplastic neurological syndromes (PNS). His multi-centre Phase II trial, currently under way, will assess the efficacy of IVIg therapy in treating PNS in the first 3 months of treatment. Dr Geis shows improved disease scores after IVIg treatment in a mouse model of neuromyelitis optica (NMO). It is hoped that these promising results will translate well into human NMO. Dr Schmidt studied IVIg therapy in an mdx mouse model for Duchenne muscular dystrophy (DMD). He reports that motor function improved and myopathic changes in skeletal muscles and creatine kinase release were decreased. Dr Gamez presents the design and rationale for a Phase II clinical trial investigating the preoperative use of IVIg therapy in myasthenia gravis patients to prevent post-operative myasthenic crisis. Dr Goebel reports results from studies elucidating the immune-mediated pathogenesis of complex regional pain syndrome (CRPS), the successful IVIg therapy in a proportion of CRPS patients, and the development of a model for predicting which patients are more likely to respond to Ig therapy.

7th International Immunoglobulin Conference: Interlaken Leadership Awards.

The research presented in this section explores novel applications of immunoglobulin (Ig) therapy in neurological disorders. The results from the upcoming and ongoing trials of Drs Honnorat and Gamez are expected to provide meaningful insights into the treatment of two serious and disabling diseases. The results already being reported from the work of Drs Schmidt and Geis in animal models seem promising, but further proof-of-concept research is warranted to translate their significance to human diseases. Dr Goebel's work in developing animal models of complex regional pain syndrome (CRPS) may provide new insights into predicting which CRPS patients could respond to Ig therapy or other immunotherapies. The work being made possible by a number of the Interlaken Leadership Awards may provide fundamental insights in understanding neurological disorders and improving quality of life for the patients who suffer from them.

Vigorimeter grip strength in CIDP: a responsive tool that rapidly measures the effect of IVIG--the ICE study.

BACKGROUND AND PURPOSE: In a recent trial in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the ICE study, grip strength measurement captured significantly more improvement in patients receiving immune globulin (IGIV-C) intravenously than in those receiving placebo. METHODS: We conducted a systematic analysis to determine the sensitivity of grip strength as an indicator of meaningful clinical changes in CIDP. RESULTS: A randomized double-blind trial was undertaken in 117 CIDP patients who received IGIV-C or placebo every 3 weeks for up to 24 weeks. Grip strength and inflammatory neuropathy cause and treatment (INCAT) disability scores were assessed at each visit, and the responsiveness of each scale was compared. A minimum clinically important difference cut-off value for grip strength (>8 kPa) and INCAT score (>1 point) was applied to assess the proportion of responders to IGIV-C versus placebo. This analysis showed that grip strength demonstrated significant improvement earlier (as early as day 16) than the INCAT disability scale in patients receiving IGIV-C compared with placebo. A significantly higher proportion of improvers were seen in the IGIV-C group (37.5%-50.9%) than in the placebo group (21.1%-25.9%) for grip strength at day 16, week 3, week 6 and the end of the first period. Also, grip strength showed within the first 6 weeks in the placebo group significantly more patients with a clinically meaningful deterioration (>8 kPa), compared with the INCAT (>1-point deterioration) findings. CONCLUSIONS: Grip strength can be considered a sensitive tool for assessing clinically relevant changes in patients with CIDP. Its use in daily practice is suggested.

Mutations in either the essential or regulatory light chains of myosin are associated with a rare myopathy in human heart and skeletal muscle.

The muscle myosins and hexomeric proteins consisting of two heavy chains and two pairs of light chains, the latter called essential (ELC) and regulatory (RLC). The light chains stabilize the long alpha helical neck of the myosin head. Their function in striated muscle, however, is only partially understood. We report here the identification of distinct missense mutations in a skeletal/ventricular ELC and RLC, each of which are associated with a rare variant of cardiac hypertrophy as well as abnormal skeletal muscle. We show that myosin containing the mutant ELC has abnormal function, map the mutant residues on the three-dimensional structure of myosin and suggest that the mutations disrupt the stretch activation response of the cardiac papillary muscles.

Missense mutations in desmin associated with familial cardiac and skeletal myopathy.

Desmin-related myopathy (OMIM 601419) is a familial disorder characterized by skeletal muscle weakness associated with cardiac conduction blocks, arrhythmias and restrictive heart failure, and by intracytoplasmic accumulation of desmin-reactive deposits in cardiac and skeletal muscle cells. The underlying molecular mechanisms are unknown. Involvement of the desmin gene (DES) has been excluded in three families diagnosed with desmin-related myopathy. We report two new families with desmin-related cardioskeletal myopathy associated with mutations in the highly conserved carboxy-terminal end of the desmin rod domain. A heterozygous A337P mutation was identified in a family with an adult-onset skeletal myopathy and mild cardiac involvement. Compound heterozygosity for two other mutations, A360P and N393I, was detected in a second family characterized by childhood-onset aggressive course of cardiac and skeletal myopathy.

Peripheral neuropathies in Sjögren's syndrome: a critical update on clinical features and pathogenetic mechanisms.

Sjögren's syndrome is a systemic autoimmune disease that, apart from exocrine glands, may affect every organ or system. Involvement of different sections of the peripheral nervous system results in a wide spectrum of neuropathic manifestations. Based on distinct clinical, electrophysiological and histological criteria, the types of neuropathies seen in Sjögren's syndrome include: a) pure sensory which presents with distal symmetric sensory loss due to axonal degeneration of sensory fibers; sensory ataxia due to loss of proprioceptive large fibers (ganglionopathy); or with painful dysethesias (small fiber sensory neuropathy) due to degeneration of cutaneous axons. The latter appears to be the most common neuropathy in Sjögren's syndrome and requires skin biopsy for diagnosis to document loss or reduction of nerve fiber density; b) sensorimotor polyneuropathy affecting sensory and motor axons, often associated with severe systemic or pro-lymhomatous manifestations, such as palpable purpura and cryoglobulinemia, and c) rare types that include autoimmune demyelinating neuropathy, mononeuropathy, mononeuropathy multiplex and autonomic neuropathy. In this review, the frequency, prevalence and diagnostic criteria for each neuropathy subset are discussed and possible pathogenetic mechanisms are outlined.

The effect of intravenous immunoglobulin (IVIG) treatment on patients with dermatomyositis: a 4-year follow-up study.

OBJECTIVES: The aim of this study is to evaluate the short- and long-term outcome of patients with dermatomyositis treated with IVIG. METHODS: Forty-two dermatomyositis patients (43 ± 19 yrs, 40.5% males) were studied; 24 of them received IVIG as an add-on treatment, while the rest received conventional immunosupression. The first follow-up point was 6 months following the initiation of treatment. Muscular and cutaneous involvement, as well as demographical and baseline data of the IVIG treated patients, were documented for a median period of 76 months (1st, 3rd quartiles 48, 108). RESULTS: Muscular remission rate was higher for IVIG treated patients at 6 months after the onset of treatment (p=0.007). During long-term follow-up, IVIG treated patients presented with low muscular and cutaneous involvement, as well as low percentages of muscular relapses. The total number of muscular relapses was inversely associated with the number of pulses (p=0.03). CONCLUSIONS: This study is a retrospective one, consisting of a small patient sample, and both muscle and skin involvement scores were developed on the basis of the clinical data provided in the patients' records. Nevertheless, it manages to demonstrate that IVIG may improve the short-term prognosis of dermatomyositis patients as compared to the classical therapies. During long-term follow-up, IVIG treated patients experienced relapses, but their muscular and cutaneous involvement scores were significantly better than their pre-treatment ones. A larger number of IVIG infusions could maintain disease remission for a longer period of time, reducing the total number of muscular relapses.

Fine specificity of antibodies against AQP4: epitope mapping reveals intracellular epitopes.

The autoantibody to aquaporin-4 (AQP4) is a marker and a pathogenetic factor in Neuromyelitis Optica (NMO) (Devic's syndrome). Our aim was to identify B-cell antigenic linear epitopes of the AQP4 protein and investigate similarities with other molecules. To this end, we screened sera from 21 patients positive for anti-AQP4 antibodies (study group), from 23 SLE and 23 pSS patients without neurologic involvement (disease controls) and from 28 healthy individuals (normal controls). Eleven peptides, spanning the entire intracellular and extracellular domains of the AQP4 molecule, were synthesized, and all sera were screened for anti-peptide antibodies by ELISA. Specificity was evaluated by homologous inhibition assays. NMO positive sera exhibited reactivity against 3 different peptides spanning the sequences aa1-22 (AQPpep1) (42.9% of patients), aa88-113 (AQPpep4) (33%) and aa252-275 (AQPpep8) (23.8%). All epitopes were localized in the intracellular domains of AQP4. Homologous inhibition rates were ranging from 71.1% to 84.3%. A 73% sequence homology was observed between AQPpep8' aa257-271, a 15-mer peptide part of the AQPpep8 aa252-275, and the aa219-233 domain of the Tax1-HTLV-1 binding protein (TAX1BP1), a host protein associated with replication of the Human T-Lymphotropic Virus 1 (HTLV-1). Antibodies against the AQP4 and the TAX1BP1 15-mer peptides were detected in 26.3% (N = 5) and 31.6% (N = 6) of NMO positive sera (r(s) = 0.81, P < 0.0001). Healthy controls did not react with these peptides, while homologous and cross-inhibition assays confirmed binding specificity. This first epitope mapping for AQP4 reveals that a significant proportion of anti-AQP4 antibodies target linear epitopes localized in the intracellular domains of the channel. One of the epitopes displays high similarity with a portion of TAX1BP1 protein.

Review: An update on inflammatory and autoimmune myopathies.

The review provides an update on the diagnosis of the main subtypes of inflammatory myopathies including dermatomyositis (DM), polymyositis (PM), necrotizing autoimmune myositis (NAM) and sporadic inclusion body myositis (sIBM). The fundamental aspects on muscle pathology and the unique pathomechanisms of each subset are outlined and the diagnostic dilemmas concerning the distinction of PM from sIBM and NAM are addressed. Dermatomyositis is a complement-mediated microangiopathy leading to destruction of capillaries, hypoperfusion and inflammatory cell stress on the perifascicular regions. NAM, is an increasingly recognized subacute myopathy triggered by statins, viral infections, cancer or autoimmuity with macrophages as the final effector cells causing fibre injury. In PM and sIBM cytotoxic CD8-positive T cells clonally expand in situ and invade major histocompatibility-I-expressing muscle fibres. The pathology of sporadic inclusion body myositis is complex because, in addition to the inflammatory mechanisms, there are degenerative features characterized by vacuolization and the accumulation of stressor and amyloid-related misfolded proteins. Inducible pro-inflammatory molecules, such as interleukin 1-ß, may enhance the accumulation of stressor proteins. The principles for more effective treatment strategies are discussed.

Mitochondrial toxicity of antiviral drugs.

Long-term treatment with antiviral nucleoside analogue drugs, such as AZT, can give rise to delayed and at times severe mitochondrial toxicity. Although these toxic effects are manifest in many tissues, a common disease mechanism can explain the diverse clinical events. A better understanding of these disorders will shed light on genetic mitochondrial diseases and lead to the design of safer and more effective antiviral drugs.

A study of the interferon antiviral mechanism: apoptosis activation by the 2-5A system.

The 2-5A system contributes to the antiviral effect of interferons through the synthesis of 2-5A and its activation of the ribonuclease, RNase L. RNase L degrades viral and cellular RNA after activation by unique, 2'-5' phosphodiester-linked, oligoadenylates [2-5A, (pp)p5' A2'(P5'A2')]n, n >=2. Because both the 2-5A system and apoptosis can serve as viral defense mechanisms and RNA degradation occurs during both processes, we investigated the potential role of RNase L in apoptosis. Overexpression of human RNase L by an inducible promoter in NIH3T3 fibroblasts decreased cell viability and triggered apoptosis. Activation of endogenous RNase L, specifically with 2-5A or with dsRNA, induced apoptosis. Inhibition of RNase L with a dominant negative mutant suppressed poly (I).poly (C)-induced apoptosis in interferon-primed fibroblasts. Moreover, inhibition of RNase L suppressed apoptosis induced by poliovirus. Thus, increased RNase L levels induced apoptosis and inhibition of RNase L activity blocked viral-induced apoptosis. Apoptosis may be one of the antiviral mechanisms regulated by the 2-5A system.

EULAR recommendations for the management of systemic lupus erythematosus with neuropsychiatric manifestations: report of a task force of the EULAR standing committee for clinical affairs.

OBJECTIVES: To develop recommendations for the diagnosis, prevention and treatment of neuropsychiatric systemic lupus erythematosus (NPSLE) manifestations. METHODS: The authors compiled questions on prevalence and risk factors, diagnosis and monitoring, therapy and prognosis of NPSLE. A systematic literature search was performed and evidence was categorised based on sample size and study design. RESULTS: Systemic lupus erythematosus (SLE) patients are at increased risk of several neuropsychiatric manifestations. Common (cumulative incidence > 5%) manifestations include cerebrovascular disease (CVD) and seizures; relatively uncommon (1-5%) are severe cognitive dysfunction, major depression, acute confusional state (ACS), peripheral nervous disorders psychosis. Strong risk factors (at least fivefold increased risk) are previous or concurrent severe NPSLE (for cognitive dysfunction, seizures) and antiphospholipid antibodies (for CVD, seizures, chorea). The diagnostic work-up of suspected NPSLE is comparable to that in patients without SLE who present with the same manifestations, and aims to exclude causes unrelated to SLE. Investigations include cerebrospinal fluid analysis (to exclude central nervous system infection), EEG (to diagnose seizure disorder), neuropsychological tests (to assess cognitive dysfunction), nerve conduction studies (for peripheral neuropathy) and MRI (T1/T2, fluid-attenuating inversion recovery, diffusion-weighted imaging, enhanced T1 sequence). Glucocorticoids and immunosuppressive therapy are indicated when NPSLE is thought to reflect an inflammatory process (optic neuritis, transverse myelitis, peripheral neuropathy, refractory seizures, psychosis, ACS) and in the presence of generalised lupus activity. Antiplatelet/anticoagulation therapy is indicated when manifestations are related to antiphospholipid antibodies, particularly thrombotic CVD. CONCLUSIONS: Neuropsychiatric manifestations in SLE patients should be first evaluated and treated as in patients without SLE, and secondarily attributed to SLE and treated accordingly.

Clinical applications of intravenous immunoglobulins in neurology.

Intravenous immunoglobulin (IVIg) is used increasingly in the management of patients with neurological conditions. The efficacy and safety of IVIg treatment in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and Guillain-Barré syndrome (GBS) have been established clearly in randomized controlled trials and summarized in Cochrane systematic reviews. However, questions remain regarding the dose, timing and duration of IVIg treatment in both disorders. Reports about successful IVIg treatment in other neurological conditions exist, but its use remains investigational. IVIg has been shown to be efficacious as second-line therapy in patients with dermatomyositis and suggested to be of benefit in some patients with polymyositis. In patients with inclusion body myositis, IVIg was not shown to be effective. IVIg is also a treatment option in exacerbations of myasthenia gravis. Studies with IVIg in patients with Alzheimer's disease have reported increased plasma anti-Abeta antibody titres associated with decreased Abeta peptide levels in the cerebrospinal fluid following IVIg treatment. These changes at the molecular level were accompanied by improved cognitive function, and large-scale randomized trials are under way.

Toxic and drug-induced myopathies.

Drugs used for therapeutic interventions either alone or in combination may sometimes cause unexpected toxicity to the muscles, resulting in a varying degree of symptomatology, from mild discomfort and inconvenience to permanent damage and disability. The clinician should suspect a toxic myopathy when a patient without a pre-existing muscle disease develops myalgia, fatigue, weakness or myoglobinuria, temporally connected to the administration of a drug or exposure to a myotoxic substance. This review provides an update on the drugs with well-documented myocytoxicity and cautions the clinicians to be alert for the potential toxicity of newly marketed drugs; highlights the clinical features and pathomechanisms of the induced muscle disease; and offers guidance on how best to treat and distinguish toxic myopathies from other acquired or hereditary muscle disorders. Practical issues regarding the diagnosis and management of statin-induced myopathies are emphasized. Myotoxicity resulting from direct insertion of transgenes to the muscle, an exciting new tool currently tested for treatment of muscular dystrophies, is also discussed.

Proinflammatory cell stress in sporadic inclusion body myositis muscle: overexpression of alphaB-crystallin is associated with amyloid precursor protein and accumulation of beta-amyloid.

BACKGROUND: In the pathology of sporadic inclusion body myositis (sIBM), the relevance of cell stress molecules such as the heat shock protein alphaB-crystallin, particularly in healthy appearing muscle fibres, has remained elusive. METHODS: 10 muscle biopsies from sIBM patients were serially stained for haematoxylin-eosin, trichrome and multi-immunohistochemistry for neural cell adhesion molecule (NCAM), alphaB-crystallin, amyloid precursor protein (APP), desmin, major histocompatibility complex I, beta-amyloid and ubiquitin. Corresponding areas of all biopsies were quantitatively analysed for all markers. Primary myotube cultures were exposed to the proinflammatory cytokines interleukin (IL)-1beta and interferon (IFN)-gamma. RESULTS: In human myotubes exposed to IL-1beta+IFN-gamma, overexpression of APP was accompanied by upregulation of alphaB-crystallin. In sIBM muscle biopsies, over 20% of all fibres displayed accumulation of beta-amyloid or vacuoles/inclusions. A clearly larger fraction of the fibres were positive for alphaB-crystallin or APP. In contrast with the accumulation of beta-amyloid in atrophic fibres, a major part of fibres positive for APP or alphaB-crystallin showed no morphological abnormalities. Expression of APP and alphaB-crystallin significantly correlated with each other and most double positive fibres displayed accumulation of beta-amyloid, vacuoles or an atrophic morphology. In almost all of these fibres, other markers of degeneration/regeneration such as NCAM and desmin were evident as additional indicators of a cell stress response. Some fibres double positive for APP and alphaB-crystallin displayed infiltration by inflammatory cells. CONCLUSION: Our results suggest that alphaB-crystallin is associated with overexpression of APP in sIBM muscle and that upregulation of alphaB-crystallin precedes accumulation of beta-amyloid. The data help to better understand early pathological changes and underscore the fact that a network of cell stress, inflammation and degeneration is relevant to sIBM.

Transmission of simian acquired immunodeficiency syndrome (SAIDS) with blood or filtered plasma.

Simian acquired immunodeficiency syndrome (SAIDS), a disease clinically and pathologically similar to acquired immunodeficiency syndrome in humans, was transmitted from diseased rhesus monkeys (Macaca mulatta) to normal monkeys by inoculation with heparinized whole blood or plasma that had been passed through filters of 0.45 micrometer pore size. This suggests that the causative agent is small and most probably a virus. No viruses, however, were isolated by standard cell culture techniques from the blood or filtered plasma which caused SAIDS. Both cellular and humoral immunity were markedly depressed in animals with advanced SAIDS.

[Targeting B cells in multiple sclerosis. Current concepts and strategies]. / B-Zell-gerichtete Multiple-Sklerose-Therapie. Aktueller Stand.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating autoimmune disease of the CNS and a leading cause of lasting neurological disability in younger adults. In the last decade our knowledge of its immunopathogenesis expanded vastly. It is now widely appreciated that B cells are key players in the autoreactive immune network. They exert far more functions than merely being the precursors of antibody-producing plasma cells. B cells act as efficient antigen-presenting cells and may stimulate an autoreactive immune response through secretion of proinflammatory cytokines. It is thus only logical to test therapeutic strategies targeting B cells in MS. Rituximab is a depleting chimeric monoclonal antibody directed against CD20 and expressed on developing, naïve, and memory B cells but not stem or plasma cells. Several smaller studies have been conducted that led to a placebo controlled, double blind phase II study on efficacy which was reported recently. The results are very promising, meeting not only the primary endpoint of reduction of the surrogate MRI marker of contrast-enhancing lesions but also showing a reduction in clinical relapse rate of patients treated with rituximab. This review discusses the role of autoreactive B cells in the context of MS, analyzes the B-cell-depleting treatment studies reported, and provides information on planned and future B-cell-directed therapeutic strategies in MS.

Induction of experimental ataxic sensory neuronopathy in cats by immunization with purified SGPG.

IgM paraproteins in about 50% of the patients with neuropathy associated with IgM gammopathy react with carbohydrate moieties in myelin-associated glycoprotein (MAG) and in sulfated glucuronic glycolipids (SGGLs) in human peripheral nerves. However, the role of anti-MAG/SGGL antibodies in the pathogenesis of neuropathy remains unclear. In order to induce an animal model of neuropathy associated with anti-MAG/SGGL antibodies, cats were immunized with sulfoglucuronyl paragloboside (SGPG). All four cats immunized with SGPG developed clinical signs of sensory neuronopathy within 11 months after initial immunization, characterized by unsteadiness, falling, hind limb weakness and ataxia. In two cats the ataxia and hind limb paralysis were so severe that the animals had to be euthanized. Pathological examination revealed sensory ganglionitis with inflammatory infiltrates in the dorsal root ganglia. No overt signs of pathology were noted in the examined roots or nerves. High titer anti-SGPG/MAG antibodies were detected in all 4 cats immunized with SGPG but not in 3 control cats. Our data demonstrate that immunization of cats with SGPG induced anti-SGPG antibodies and sensory neuronopathy clinically resembling the sensory ataxia of patients with monoclonal IgM anti-MAG/SGPG antibodies. This study suggests that these anti-MAG/SGPG antibodies play a role in the pathogenesis of this neuropathy.

High-dose intravenous immunoglobulin exerts its beneficial effect in patients with dermatomyositis by blocking endomysial deposition of activated complement fragments.

In patients with dermatomyositis (DM) the earliest lesion is microvasculopathy mediated by deposition of C5b-C9 membranolytic attack complex (MAC) on intramuscular capillaries. This leads sequentially to muscle ischemia, necrosis of muscle fibers, and muscle weakness. High-dose intravenous immunoglobulin (IVIG), which can modulate complement-dependent tissue damage in animal models, has been shown to be effective in the treatment of patients with DM. We used an in vitro C3 uptake assay to examine 55 coded sera from 13 patients with DM and 5 patients with other non-complement-mediated neuromuscular diseases, before and after treatment with IVIG or placebo. Patients with active DM had a significantly higher baseline C3 uptake compared with the others (geometric mean 12,190 vs 3,090 cpm). Post-IVIG but not post-placebo sera inhibited the C3 uptake, without depleting the complement components, by 70.6-93.4%. The maximum inhibition of C3 uptake occurred within hours after IVIG infusion, started to rebound 2 d later, and reached pretreatment levels after 30 d. The serum levels of SC5b-9 complex production were high at baseline but normalized after IVIG therapy. Repeat biopsies from muscles of improved patients showed disappearance of C3b NEO and MAC deposits from the endomysial capillaries and restoration of the capillary network. We conclude that IVIG exerts its beneficial clinical effect by intercepting the assembly and deposition of MAC on the endomysial capillaries through the formation of complexes between the infused immunoglobulins and C3b, thereby preventing the incorporation of activated C3 molecules into C5 convertase. These findings provide the first serological and in situ evidence that IVIG modulates complement attack in a human disease.