The Role of Complement in Cryoglobulin-Induced Immune Complex Glomerulonephritis

Novel aspects in the pathophysiology and diagnosis of glomerular diseases

Immune deposits/complexes are detected in a multitude of tissues in autoimmune disorders, but no organ has attracted as much attention as the kidney. Several kidney diseases are characterised by the presence of specific configurations of such deposits, and many of them are under a 'shared care' between rheumatologists and nephrologists. This review focuses on five different diseases commonly encountered in rheumatological and nephrological practice, namely IgA vasculitis, lupus nephritis, cryoglobulinaemia, anti-glomerular basement membrane disease and anti-neutrophil cytoplasm-antibody glomerulonephritis. They differ in disease aetiopathogenesis, but also the potential speed of kidney function decline, the responsiveness to immunosuppression/immunomodulation and the deposition of immune deposits/complexes. To date, it remains unclear if deposits are causing a specific disease or aim to abrogate inflammatory cascades responsible for tissue damage, such as neutrophil extracellular traps or the complement system. In principle, immunosuppressive therapies have not been developed to tackle immune deposits/complexes, and repeated kidney biopsy studies found persistence of deposits despite reduction of active inflammation, again highlighting the uncertainty about their involvement in tissue damage. In these studies, a progression of active lesions to chronic changes such as glomerulosclerosis was frequently reported. Novel therapeutic approaches aim to mitigate these changes more efficiently and rapidly. Several new agents, such as avacopan, an oral C5aR1 inhibitor, or imlifidase, that dissolves IgG within minutes, are more specifically reducing inflammatory cascades in the kidney and repeat tissue sampling might help to understand their impact on immune cell deposition and finally kidney function recovery and potential impact of immune complexes/deposits.

C1q as a target molecule to treat human disease: What do mouse studies teach us?

The complement system is a field of growing interest for pharmacological intervention. Complement protein C1q, the pattern recognition molecule at the start of the classical pathway of the complement cascade, is a versatile molecule with additional non-canonical actions affecting numerous cellular processes. Based on observations made in patients with hereditary C1q deficiency, C1q is protective against systemic autoimmunity and bacterial infections. Accordingly, C1q deficient mice reproduce this phenotype with susceptibility to autoimmunity and infections. At the same time, beneficial effects of C1q deficiency on disease entities such as neurodegenerative diseases have also been described in murine disease models. This systematic review provides an overview of all currently available literature on the C1q knockout mouse in disease models to identify potential target diseases for treatment strategies focusing on C1q, and discusses potential side-effects when depleting and/or inhibiting C1q.

The rational use of complement inhibitors in kidney diseases

The development of complement inhibitors represented one of the major breakthroughs in clinical nephrology in the last decade. Complement inhibition has dramatically transformed the outcome of one of the most severe kidney diseases, the atypical hemolytic uremic syndrome (aHUS), a prototypic complement-mediated disorder. The availability of complement inhibitors has also opened new promising perspectives for the management of several other kidney diseases in which complement activation is involved to a variable extent. With the rapidly growing number of complement inhibitors tested in a rapidly increasing number of indications, a rational use of this innovative and expensive new therapeutic class has become crucial. The present review aims to summarize what we know, and what we still ignore, regarding complement activation and therapeutic inhibition in kidney diseases. It also provides some clues and elements of thoughts for a rational approach of complement modulation in kidney diseases.

Role of ADCC, CDC, and CDCC in Vaccine-Mediated Protection against Her2 Mammary Carcinogenesis

Amplification or mutation of the Her2 oncoantigen in human mammary glands leads to the development of an aggressive breast carcinoma. Several features of this breast carcinoma are reproduced in mammary carcinomas that spontaneously arise in female transgenic mice bearing the activated rat Her2 oncogene under transcriptional control of the mouse mammary tumor virus promoter-BALB-neuT (neuT) mice. We previously demonstrated that carcinoma progression in neuT mice can be prevented by DNA vaccination with RHuT, a plasmid coding for a chimeric rat/human Her2 protein. RHuT vaccination exerts an antitumor effect, mostly mediated by the induction of a strong anti-rat Her2 antibody response. IgG induced by RHuT vaccine mainly acts by blocking Her2 signaling, thus impairing cell cycle progression and inducing apoptosis of cancer cells, but other indirect effector mechanisms could be involved in the antibody-mediated protection. The recruitment of cells with perforin-dependent cytotoxic activity, able to perform antibody-dependent cellular cytotoxicity, has already been investigated. Less is known about the role of the complement system in sustaining antitumor response through complement-dependent cytotoxicity and cellular cytotoxicity in vaccinated mice. This work highlights that the weight of such mechanisms in RHuT-induced cancer protection is different in transplantable versus autochthonous Her2⁺ tumor models. These results may shed new light on the effector mechanisms involved in antibody-dependent anti-cancer responses, which might be exploited to ameliorate the therapy of Her2⁺ breast cancer.

The Successful Treatment of a Case of HCV-associated Cryoglobulinemic Glomerulonephritis with Rituximab, Direct-acting Antiviral Agents, Plasmapheresis and Long-term Steroid Despite Serologically Persistent Cryoglobulinemia

Novel treatments with rituximab or direct-acting antiviral agents (DAAs) were expected to improve the clinical outcomes of hepatitis C virus (HCV)-associated cryoglobulinemia in the last decade. Recently, however, persistent cases of cryoglobulinemia have been reported, and the ideal approach to treating such cases has not been established. We herein report a case of the successful treatment of HCV-associated cryoglobulinemic glomerulonephritis with rituximab, DAAs, occasional plasmapheresis and long-term steroid, with the patient's renal function and proteinuria improving over the long term despite serologically persistent cryoglobulinemia. This case suggests the efficacy of combination treatment with rituximab, DAAs, occasional plasmapheresis and long-term steroid for persistent cryoglobulinemia.

Liver-Specific siRNA-Mediated Stat3 or C3 Knockdown Improves the Outcome of Experimental Autoimmune Myocarditis

Myocarditis can lead to autoimmune disease, dilated cardiomyopathy, and heart failure, which is modeled in the mouse by cardiac myosin immunization (experimental autoimmune myocarditis [EAM]). Signal transducer and activator of transcription 3 (STAT3) systemic inhibition exerts both preventive and therapeutic effects in EAM, and STAT3 constitutive activation elicits immune-mediated myocarditis dependent on complement C3 and correlating with activation of the STAT3-interleukin 6 (IL-6) axis in the liver. Thus, liver-specific STAT3 inhibition may represent a therapeutic option, allowing to bypass the heart toxicity, predicted by systemic STAT3 inhibition. We therefore decided to explore the effectiveness of silencing liver Stat3 and C3 in preventing EAM onset and/or the recovery of cardiac functions. We first show that complement C3 and C5 genetic depletion significantly prevents the onset of spontaneous myocarditis, supporting the complement cascade as a viable target. In order to interfere with complement production and STAT3 activity specifically in the liver, we took advantage of liver-specific Stat3 or C3 small interfering (si)RNA nanoparticles, demonstrating that both siRNAs can significantly prevent myocarditis onset and improve the recovery of heart functions in EAM. Our data demonstrate that liver-specific Stat3/C3 siRNAs may represent a therapeutic option for autoimmune myocarditis and suggest that complement levels and activation might be predictive of progression to dilated cardiomyopathy.

Cryoglobulinemic Glomerulonephritis Associated With Nodal and Renal Infiltration by T-Cell Lymphoma of T-Follicular Helper Phenotype: A Case Report

We present a unique case of cryoglobulinemic glomerulonephritis associated with nodal and renal infiltration by T-cell lymphoma of T-follicular helper phenotype. The patient presented with transient neurologic symptoms, severe nephritic syndrome with nephrotic-range proteinuria, and acute kidney injury. He had elevated double-stranded DNA levels, low complement levels, detectable cryoglobulin, and detectable immunoglobulin M (IgM) paraprotein. The kidney biopsy showed cryoglobulinemic glomerulonephritis with a membranoproliferative pattern and diffuse interstitial infiltrates on light microscopy; IgM, C3 but weak IgG, C1q, and negative C4d staining on immunofluorescence; and deposits with organized substructures on electron microscopy. Positron emission tomography showed diffuse uptake in bilaterally enlarged kidneys and a localized group of lymph nodes. Subsequent lymph node biopsy revealed Epstein-Barr virus-negative nodal T-cell lymphoma, which was also proven in renal tissue. The association between T-cell lymphoma, autoantibodies, and cryoglobulinemia may represent a paraneoplastic phenomenon. His renal prognosis has been excellent, but overall prognosis and survival is dictated by the clinical course of T-cell lymphoma.

[Renal involvement of cryoglobulinemia]

Cryoglobulins are immunoglobulins that undergo reversible precipitation at low temperatures. They can induce systemic vasculitis, characterized by purpuric cutaneous lesions, arthritis, peripheral neuropathy, hypocomplementemia and glomerular disease. Renal pathology reveals membranoproliferative glomerulonephritis, with particularly intense mesangial cell proliferation and infiltration by macrophages, associated with intracapillary thrombi. This renal disease presents as a nephritic syndrome, with heavy proteinuria, haematuria severe hypertension and rapidly progressive kidney failure that can lead to end-stage renal disease. Hepatitis C is the main cause of mixed (type 2 or 3) cryoglobulinemia and requires the initiation of a specific antiviral therapy, together with immunosuppressive drugs. Rituximab is now considered as the best immunosuppressive therapy in this situation, inducing B-cell depletion, clearance of circulating cryoglobulin and resolution of renal symptoms. Monoclonal (type 1) cryoglobulinemia, is a rare condition, but it usually reveals an B-cell or a plasma cell proliferation, that require a specific hematological treatment to obtain remission of the renal disease.

Re-Examining Neutrophil Participation in GN

Significant advances in understanding the pathogenesis of GN have occurred in recent decades. Among those advances is the finding that both innate and adaptive immune cells contribute to the development of GN. Neutrophils were recognized as key contributors in early animal models of GN, at a time when the prevailing view considered neutrophils to function as nonspecific effector cells that die quickly after performing antimicrobial functions. However, advances over the past two decades have shown that neutrophil functions are more complex and sophisticated. Specifically, research has revealed that neutrophil survival is regulated by the inflammatory milieu and that neutrophils demonstrate plasticity, mediate microbial killing through previously unrecognized mechanisms, demonstrate transcriptional activity leading to the release of cytokines and chemokines, interact with and regulate cells of the innate and adaptive immune systems, and contribute to the resolution of inflammation. Therefore, neutrophil participation in glomerular diseases deserves re-evaluation. In this review, we describe advances in understanding classic neutrophil functions, review the expanded roles of neutrophils in innate and adaptive immune responses, and summarize current knowledge of neutrophil contributions to GN.

The non-inflammatory role of C1q during Her2/neu-driven mammary carcinogenesis

There is an ever increasing amount of evidence to support the hypothesis that complement C1q, the first component of the classical complement pathway, is involved in the regulation of cancer growth, in addition to its role in fighting infections. It has been demonstrated that C1q is expressed in the microenvironment of various types of human tumors, including breast adenocarcinomas. This study compares carcinogenesis progression in C1q deficient (neuT-C1KO) and C1q competent neuT mice in order to investigate the role of C1q in mammary carcinogenesis. Significantly accelerated autochthonous neu⁺ carcinoma progression was paralleled by accelerated spontaneous lung metastases occurrence in C1q deficient mice. Surprisingly, this effect was not caused by differences in the tumor-infiltrating cells or in the activation of the complement classical pathway, since neuT-C1KO mice did not display a reduction in C3 fragment deposition at the tumor site. By contrast, a significant higher number of intratumor blood vessels and a decrease in the activation of the tumor suppressor WW domain containing oxidoreductase (WWOX) were observed in tumors from neuT-C1KO as compare with neuT mice. In parallel, an increase in Her2/neu expression was observed on the membrane of tumor cells. Taken together, our findings suggest that C1q plays a direct role both on halting tumor angiogenesis and on inducing apoptosis in mammary cancer cells by coordinating the signal transduction pathways linked to WWOX and, furthermore, highlight the role of C1q in mammary tumor immune surveillance regardless of complement system activation.

Coagulation disorders and their cutaneous presentations: Pathophysiology

Hypercoagulable states are inherited or acquired predispositions to venous or arterial thromboses that are best understood in the context of the coagulation cascade. Dermatologists can play a critical role in diagnosing and treating patients with hypercoagulable states because cutaneous symptoms may be a presenting manifestation, thereby reducing morbidity and mortality related to these conditions. This review focuses on the epidemiology and pathophysiology of hypercoagulable states, while the accompanying article iterates the basic clinical features, diagnostic testing, and management of patients who have these conditions.

Diagnostics and treatment of cryoglobulinaemia: it takes two to tango

Cryoglobulins are immunoglobulins that reversibly precipitate in the cold. They come in different flavours and, as such, are differentially associated with lymphoproliferative diseases (type I), or systemic autoimmune diseases, and/or infectious diseases (type II/III). The clinical manifestations of cryoglobulinaemia result from either hyper-viscosity or small vessel vasculitis. Hepatitis C virus (HCV) is a well-known factor in the aetiology of cryoglobulinaemia, but substantial geographical differences exist in the association between cryoglobulins and HCV. In the absence of any underlying disease, cryoglobulinaemia is referred to as 'idiopathic' or 'essential'. Detection of cryoglobulins in the laboratory is hampered by several pitfalls, in particular in the pre-analytical stage as well as in the quantification. In addition, our personal experience reveals that the detection of rheumatoid factor, most often present in high concentrations in patients with mixed cryoglobulinaemia, relies on the choice of the test system. Hence, interpretation of the laboratory results in relation to the clinical manifestations requires a partnership between the clinician and the laboratory specialist in order to make a correct diagnosis. Treatment options are primarily directed by identification of underlying diseases, i.e. infections or systemic autoimmune diseases. Idiopathic cryoglobulinaemia is treated with corticosteroids and immunosuppression, or B cell depleting anti-CD20 biologicals. In this overview, the recent literature on current laboratory and clinical practice of cryoglobulinaemia is discussed from a personal perspective.

IgG1 deficiency exacerbates experimental autoimmune myasthenia gravis in BALB/c mice

Myasthenia gravis is an autoimmune disease characterized by muscle weakness due to neuromuscular junction (NMJ) damage by anti-acetylcholine receptor (AChR) auto-antibodies and complement. In experimental autoimmune myasthenia gravis (EAMG), which is induced by immunization with Torpedo AChR in CFA, anti-AChR IgG2b and IgG1 are the predominant isotypes in the circulation. Complement activation by isotypes such as IgG2b plays a crucial role in EAMG pathogenesis; this suggested the possibility that IgG1, which does not activate complement through the classical pathway, may suppress EAMG. In this study, we show that AChR-immunized BALB/c mice genetically deficient for IgG1 produce higher levels of complement-activating isotypes of anti-AChR, especially IgG3 and IgG2a, and develop increased IgG3/IgG2a deposits at the NMJ, as compared to wild type (WT) BALB/c mice. Consistent with this, AChR-immunized IgG1(-/-) BALB/c mice lose muscle strength and muscle AChR to a greater extent than AChR-immunized WT mice. These observations demonstrate that IgG1 deficiency leads to increased severity of EAMG associated with an increase in complement activating IgG isotypes. Further studies are needed to dissect the specific role or mechanism of IgG1 in limiting EAMG and that of EAMG exacerbating role of complement activating IgG3 and IgG2a in IgG1 deficiency.

Expression of macrophage markers in cryoglobulinemic glomerulonephritis - a possible role of CXCL9

PURPOSE

Cryoglobulinemic glomerulonephritis (CGGN) is a type of membranoproliferative glomerulonephritis (MPGN) that develops in patients with systemic cryoglobulinemia. To date the exact pathogenesis of CGGN remains unclear. It has been suggested that macrophages may be significant contributors to the glomerular injury in this disease. In our study we attempt to characterize the macrophages in human CGGN using classical activation and regulatory macrophage markers.

MATERIAL AND METHOD

We searched our database for renal biopsy cases of CGGN. Macrophages were detected using a monoclonal anti-CD68 antibody. Two groups of macrophage markers were used: classical activation markers, including iNOS, CXCL9 and CCL20, and regulatory markers: SPHK1 and LIGHT. The stains were performed using immunohistochemical method.

RESULTS

Five patients with CGGN were identified. Four patients had systemic cryoglobulinemia and two had a serological evidence of hepatitis C virus infection. In all cases the glomeruli contained numerous macrophages. Staining for activatory macrophage markers revealed a strong nuclear staining for CXCL9 in numerous cells, including those corresponding to the macrophage location. Staining for the other activatory markers, as well as staining for regulatory markers, was not significant.

CONCLUSION

In this study of human CGGN we showed a striking expression of cytokine CXCL9, a classical macrophage activation marker, by the macrophages and possibly other cell types within the glomeruli. This observation points to the possible role of classically activated macrophages in the pathogenesis of MPGN. If this observation is confirmed on a larger group of patients, the cytokine CXCL9 could become a potential therapeutic target for human CGGN.

O-linked glycosylation determines the nephritogenic potential of IgA rheumatoid factor

Deficient glycosylation of O-linked glycans in the IgA1 hinge region is associated with IgA nephropathy in humans, but the pathogenic contribution of the underlying structural aberrations remains incompletely understood. We previously showed that mice implanted with cells secreting the class-switch variant 6-19 IgA anti-IgG2a rheumatoid factor, but not 46-42 IgA anti-IgG2a rheumatoid factor, develop glomerular lesions resembling IgA nephropathy. Because the levels of O-linked glycosylation in the hinge region and the structures of N-linked glycans in the CH1 domain differ in 6-19 IgA and 46-42 IgA, we determined the respective contributions of O- and N-linked glycans to the nephritogenic potential of the 6-19 IgA rheumatoid factor in mice. Wild-type 6-19 IgA secreted by implanted cells induced significant formation of glomerular lesions, whereas poorly O-glycosylated 6-19 IgA glycovariants or a 6-19 IgA hinge mutant lacking O-linked glycans did not. However, we observed no apparent heterogeneity in the structure of N-linked glycans attached to three different sites of the Fc regions of nephritogenic and non-nephritogenic 6-19 IgAs. Collectively, our data suggest a critical role of O-linked glycans attached to the hinge region in the development of IgA nephropathy-like GN induced by 6-19 IgA rheumatoid factor in mice.

Early onset and enhanced growth of autochthonous mammary carcinomas in C3-deficient Her2/neu transgenic mice

Aside from its classical role in fighting infections, complement is an important, although poorly understood, component of the tumor microenvironment. In particular, the tumor growth-regulatory activities of complement remain under debate. To assess the role of the complement system in the progression of autochthonous mammary carcinomas, we have crossed complement component 3 (C3)-deficient (C3^−/−) BALB/c male mice with BALB/c females expressing the activated rat Her2/neu oncogene (neuT). Although neuT transgenic mice develop spontaneous mammary cancers with 100% penetrance, a significantly shorter tumor latency (i.e., earlier onset of the first palpable tumor), a higher frequency of multiple tumors (multiplicity), and a dramatic increase in the tumor growth rate were found in neuT-C3^−/− animals. The accelerated tumor onset observed in neuT-C3^−/− mice was paralleled by an earlier onset of spontaneous lung metastases and by an increase in Her2 expression levels, primarily on the surface of tumor cells. The percentage of immune cells infiltrating neuT carcinomas was similar in C3-deficient and C3-proficient mice, with the exception of a significant increase in the frequency of regulatory T cells in neuT-C3^−/− tumors. Of particular interest, the enhanced immunosuppression imparted by C3 deficiency clearly influenced the immunogenic phenotype of autochthonous mammary tumors as neuT-C3^−/− malignant cells transplanted into syngeneic immunocompetent hosts gave rise to lesions with a significantly delayed kinetics and reduced incidence as compared with cells obtained from neuT C3-proficient tumors. Finally, increased blood vessel permeability was evident in neuT-C3^−/− tumors, although a similar number of tumor vessels was found in neuT and neuT-C3^−/− lesions. Altogether, these data suggest that complement plays a crucial role in the immunosurveillance and, possibly, the immunoediting of Her2-driven autochthonous mammary tumors.

Renal involvement in HCV-related vasculitis

Renal involvement has been frequently reported in the setting of hepatitis C virus (HCV) infection. The most common renal pathology associated with chronic HCV infection is type I membranoproliferative glomerulonephritis associated with type II mixed cryoglobulinemia, while membranoproliferative glomerulonephritis without cryoglobulinemia and membranous nephropathy were less frequently reported. Rarely, focal segmental glomerulosclerosis, fibrillary and immunotactoid glomerulopathies, and thrombotic microangiopathies were described during the course of HCV infection. In the present review, we have focused on renal involvement in HCV-related vasculitis.

Hepatitis C virus infection, mixed cryoglobulinemia, and kidney disease

Hepatitis C virus (HCV) may instigate mixed cryoglobulinemia; the most significant accompanying kidney lesion is type I membranoproliferative glomerulonephritis, usually occurring in the context of type II mixed cryoglobulinemia. Additionally, recent data support a link between HCV infection and proteinuria in population-based studies, raising the possibility that kidney diseases associated with HCV may be more common than previously thought. A number of strategies have been used to treat HCV-related glomerulonephritis, including antiviral agents, immunosuppressive therapies such as corticosteroids and cytotoxic agents, and plasma exchange. Limited but encouraging data about the utility of antiviral treatment in the setting of HCV-associated glomerulonephritis exist, with one pooled analysis noting a sustained viral response of 42%, albeit with significant heterogeneity. Immunosuppressive therapy may be most useful for cryoglobulinemic kidney disease, with individualized approaches considered for the treatment of HCV-associated cryoglobulinemic glomerulonephritis based on the level of proteinuria and kidney failure. Of note, rituximab, a chimeric monoclonal antibody that blocks CD20 receptors on B cells, has been reported to be effective for the treatment of mixed cryoglobulinemia symptoms, including glomerulonephritis.

A trial of complement inhibition in a patient with cryoglobulin-induced glomerulonephritis

Cryoglobulinemia induces an immune complex-mediated glomerulonephritis that is characterized by the presence of large immune deposits, including complement C3 and C5b-9, marked macrophage influx and mesangial cell proliferation. The precise role of complement in cryoglobulin-induced glomerulonephritis in humans remains unclear, whereas in mice there has been evidence that complement activation might be a central factor favoring glomerular inflammation, particularly by the recruitment of neutrophils. We report on an exceptional case of cryoglobulin-induced glomerulonephritis in a patient with mixed essential cryoglobulinemia type II. The clinical features included relapsing proteinuria and renal function impairment that were controlled by plasmapheresis. Complement was low in plasma and two renal biopsies at 1-year interval showed prominent immunoglobulin and complement deposits, with unusual high numbers of neutrophils. In a 1-patient clinical trial, we tested whether the monoclonal anti-C5 antibody eculizumab would be sufficient to control renal function at the time of a relapse. Although during the initial weeks renal function was stabilized, slow increase in creatinine could not be controlled by this treatment, so that plasmapheresis was reinstituted. This result suggests that despite evidence for a role of complement in enhancing renal damage in this patient, other inflammatory processes dominated.

O-glycosylated IgA rheumatoid factor induces IgA deposits and glomerulonephritis

Structural aberrations of O-linked glycans present in the IgA1 hinge region are associated with IgA nephropathy, but their contribution to its pathogenesis remains incompletely understood. In this study, mice implanted with hybridoma secreting 6-19 IgA anti-IgG2a rheumatoid factor, but not 46-42 IgA rheumatoid factor bearing the same IgA allotype, developed mesangial deposits consisting of IgA, IgG2a, and C3. Studies in immunoglobulin- and C3-deficient mice revealed that the development of these glomerular lesions required the formation of IgA-IgG2a immune complexes and subsequent activation of complement. The proportion of polymeric and monomeric forms, the IgG2a-binding affinity, and the serum levels of IgA-IgG2a immune complexes were similar between 6-19 IgA- and 46-42 IgA-injected mice. In contrast, the analysis of oligosaccharide structures revealed highly galactosylated O-linked glycans in the hinge region of 6-19 IgA and poorly O-glycosylated in the hinge region of 46-42 IgA. Furthermore, the structure of N-linked glycans in the CH1 domain was the complex type in 6-19 IgA and the hybrid type in 46-42 IgA. In summary, this study demonstrates the presence of O-linked glycans in the hinge region of mouse IgA and suggests that 6-19 IgA rheumatoid factor-induced GN could serve as an experimental model for IgA nephropathy.

Proliferative glomerulonephritis secondary to dysfunction of the alternative pathway of complement

BACKGROUND AND OBJECTIVES

dense deposit disease (DDD) is the prototypical membranoproliferative glomerulonephritis (MPGN), in which fluid-phase dysregulation of the alternative pathway (AP) of complement results in the accumulation of complement debris in the glomeruli, often producing an MPGN pattern of injury in the absence of immune complexes. A recently described entity referred to as GN with C3 deposition (GN-C3) bears many similarities to DDD. The purpose of this study was to evaluate AP function in cases of GN-C3.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Five recent cases of MPGN with extensive C3 deposition were studied. Renal biopsy in one case exhibited the classic findings of DDD. Three cases showed GN-C3 in the absence of significant Ig deposition; however, the classic hallmark of DDD-dense deposits along the glomerular basement membranes and mesangium-was absent. The remaining case exhibited features of both DDD and GN-C3.

RESULTS

Evidence of AP activation was demonstrable in all cases and included increased levels of soluble membrane attack complex (all cases), positive AP functional assays (four cases), and a positive hemolytic assay (one case). Autoantibodies were found to C3 convertase (two cases) and to factor H (one case). Factor H mutation screening identified the H402 allele (all cases) and a c.C2867T p.T956M missence mutation (one case). Laser microdissection and mass spectrometry of glomeruli of GN-C3 (two cases) showed a proteomic profile very similar to DDD.

CONCLUSIONS

These studies implicate AP dysregulation in a spectrum of rare renal diseases that includes GN-C3 and DDD.

Rituximab may form a complex with IgMkappa mixed cryoglobulin and induce severe systemic reactions in patients with hepatitis C virus-induced vasculitis

OBJECTIVE

To report on 6 cases of hepatitis C virus (HCV)-induced mixed cryoglobulinemia (MC) vasculitis in patients who developed severe systemic reactions after rituximab infusion, and to report the results of the in vitro analysis of the underlying immunologic mechanisms.

METHODS

Twenty-two HCV-infected patients with MC vasculitis received rituximab infusions (a low-dose protocol cycle with 375 mg/m2/week for 4 consecutive weeks in 18 patients and a high-dose protocol cycle with 1,000 mg on days 1 and 15 in 4 patients). Systemic drug reactions following rituximab infusion were recorded and analyzed clinically and immunochemically.

RESULTS

Six of 22 patients (27.3%) experienced systemic drug reactions after rituximab infusion. Four patients developed a severe flare of MC vasculitis 1 or 2 days after rituximab infusion. Two patients developed serum sickness syndrome 7 and 9 days after the first 1,000 mg rituximab infusion. Compared with patients without drug reactions, those with drug reactions had higher mixed cryoglobulin levels (mean+/-SD 1.4+/-0.82 gm/liter versus 0.71+/-0.77 gm/liter; P=0.0475) and lower C4 levels (mean+/-SD 0.02+/-0.006 gm/liter versus 0.07+/-0.07 gm/liter; P=0.02), and more of them received 1,000 mg high-dose rituximab protocol (50% versus 6.25%; P=0.046). In vitro immunochemical assays showed that rituximab formed a complex with the cryoprecipitating IgMkappa that had rheumatoid factor (RF) activity. Moreover, the in vitro addition of rituximab to serum containing an RF-positive IgMkappa type II mixed cryoglobulin was associated with visibly accelerated cryoprecipitation.

CONCLUSION

In HCV-associated MC vasculitis, rituximab may form a complex with RF-positive IgMkappa, leading to accelerated cryoprecipitation and to severe systemic reactions. Rituximab should be administered with caution in MC vasculitis, with use of the 375 mg protocol and plasma exchanges prior to rituximab infusion in patients with high baseline levels of mixed cryoglobulin.

Autoantibodies against C1q in systemic lupus erythematosus are antigen-driven

Autoantibodies against complement C1q (anti-C1q Abs) were shown to strongly correlate with the occurrence of severe nephritis in patients with systemic lupus erythematosus (SLE), suggesting a potential pathogenic role by interfering with the complement cascade. To analyze the humoral immune response against C1q at the molecular level, we screened a bone marrow-derived IgGkappa/IgGlambda Fab phage display library from a SLE patient with high anti-C1q Ab titer against purified human C1q. Six Fabs that exhibited strong binding to C1q in ELISA were isolated. The anti-C1q Fabs recognized neoepitopes that were only exposed on bound C1q and not present on soluble C1q mapping to different regions of the collagen-like region of C1q. Analysis of the genes encoding the variable H and L chains of the IgG-derived anti-C1q Fab revealed that all the variable H and L chain regions were highly mutated, with nucleotide and amino acid homologies to the closest germline in the range of 71-97% (average 85 +/- 4) and 72-92% (average 88 +/- 6), respectively. In addition, the variable region of the Fabs exhibited high replacement to silent ratios. The six anti-C1q Fabs were shown to be of high affinity, with a K(d) ranging from of 8.4 x 10(-8) M to 1.4 x 10(-7) M, comparable to an antiviral immune response. Our data underlines the notion that the development of anti-C1q Abs in SLE is the consequence of an Ag-driven, affinity-matured immune response. Those anti-C1q Fabs are unique tools to address how complement C1q is implicated in the pathogenesis of SLE.

Murine IgG1 and IgG3 isotype switch variants promote phagocytosis of Cryptococcus neoformans through different receptors

Almost 3 decades ago, murine IgG3 was proposed to interact with a different receptor than the other IgG subclasses, but the issue remains unresolved. The question of whether a specific receptor exists for IgG3 is critically important for understanding Ab-mediated immunity against Cryptococcus neoformans, where the different isotypes manifest profound differences in protective efficacy. In this study, we revisited this question by analyzing IgG1- and IgG3-mediated phagocytosis with variable region-identical mAbs using mouse macrophages deficient in various receptors and in conditions of FcgammaR and complement receptor blockage with specific Abs. IgG3 was an efficient opsonin for C. neoformans in FcgammaR- and CD18-deficient cells and in the presence of blocking Abs to FcgammaR and complement receptor. Like IgG1, IgG3-mediated phagocytosis was associated with fungal residence in a mature phagosome that was followed by intracellular replication and exocytosis events. We conclude that a specific receptor for IgG3 exists in mice that is structurally different from the known FcgammaRs.

Both complement and IgG fc receptors are required for development of attenuated antiglomerular basement membrane nephritis in mice

To elucidate the mechanisms of glomerulonephritis, including Goodpasture's syndrome, mouse models are used that use heterologous Abs against the glomerular basement membrane (GBM) with or without preimmunization with foreign IgG from the same species. These studies have revealed the requirement of either FcgammaR or complement, depending on the experimental model used. In this study, we provide evidence that both FcgammaR and complement are obligatory for a full-blown inflammation in a novel attenuated passive model of anti-GBM disease. We demonstrate that administration of subnephritogenic doses of rabbit anti-GBM Abs followed by a fixed dose of mouse mAbs to rabbit IgG, allowing timing and dosing for the induction of glomerulonephritis, resulted in reproducible complement activation via the classical pathway of complement and albuminuria in wild-type mice. Because albuminuria was absent in FcR-gamma-chain(-/-) mice and reduced in C3(-/-) mice, a role for both FcgammaR and complement is postulated. Because C1q(-/-) and C4(-/-) mice lacking a functional classical and lectin pathway did develop albuminuria, we suggest involvement of the alternative pathway of complement. Anti-GBM glomerulonephritis occurs acutely following the administration of mouse anti-rabbit IgG, and proceeds in a chronic fashion dependent on both FcgammaR and complement. This novel attenuated model allows elucidating the relative contribution of different mediator systems of the immune system to the development of renal injury, and also provides a platform for the assessment of different treatment protocols and evaluation of drugs that ultimately may be beneficial for the treatment of anti-GBM mediated glomerulonephritides.

Salmonella flagellins are potent adjuvants for intranasally administered whole inactivated influenza vaccine

Bacterial flagellins are potent inducers of innate immune responses in the mouse lung because they bind to TLR5 expressed on the apical surfaces of airway epithelial cells. TLR engagement leads to the initiation of a signaling cascade that results in a pro-inflammatory response with subsequent up-regulation of several cytokines and leads to adaptive immune responses. We examined the ability of two soluble flagellins, a monomeric flagellin expressed in Escherichia coli and a highly purified polymeric flagellin directly isolated from Salmonella, to enhance the efficacy of influenza vaccines in mice. Here we demonstrate that both flagellins co-administered intranasally with inactivated A/PR/8/34 (PR8) virus induced robust increases of systemic influenza-specific IgA and IgG titers and resulted in a more comprehensive humoral response as indicated by the increase of IgG2a and IgG2b subclass responses. Groups immunized with the adjuvanted vaccines were fully protected against high dose lethal challenge by homologous virus whereas inactivated PR8 alone conferred only partial protection. Finally we show that shortly after immunization the adjuvanted vaccines induced a dramatic increase in pro-inflammatory cytokines in the lung, resulting in extensive lung infiltration by granulocytes and monocytes/macrophages. Our results reveal a promising perspective for the use of both soluble monomeric and polymeric flagellin as mucosal vaccine adjuvants to improve protection against influenza epidemics as well as a range of other infectious diseases.

New insights into intra- and intermolecular interactions of immunoglobulins: crystal structure of mouse IgG2b-Fc at 2.1-A resolution

The structure of the Fc fragment of monoclonal antibody IgG2b from hybridom M75 of Mus musculus has been determined by single crystal X-ray diffraction. This is the first report of the structure of the murine immunoglobulin isotype IgG2b. The structure refined at 2.1 A resolution provides more detailed structural information about native oligosaccharides than was previously available. High-quality Fourier maps provide a clear identification of alpha-l-fucose with partial occupancy in the first branch of the antennary oligosaccharides. A unique Fc:Fc interaction was observed at the C(H)2-C(H)3 interface.

Peanuts can contribute to anaphylactic shock by activating complement

BACKGROUND

Peanut allergy is the most common food-related cause of lethal anaphylaxis and, unlike other food allergies, typically persists into adulthood. Resistance to digestion and dendritic cell activation by the major peanut allergen Ara h 1 are reported to contribute to its allergenicity.

OBJECTIVE

We sought to evaluate whether peanut molecules might also promote anaphylaxis through an innate immune mechanism.

METHODS

Naive mice were treated with a beta-adrenergic receptor antagonist and long-acting IL-4 to increase sensitivity to vasoactive mediators and injected with peanut extract (PE). Shock was detected and quantified by means of rectal thermometry. Gene-deficient mice and specific antagonists were used to determine the roles of specific cell types, complement, Fc receptors, and vasoactive mediators in shock pathogenesis.

RESULTS

PE induces dose-dependent shock. PE activates complement in vivo in mice and in vitro in mice and human subjects. C3a and, to a lesser extent, stimulatory immunoglobulin receptors contribute to PE-induced shock. PE-induced shock depends more on macrophages and basophils than on mast cells. Platelet-activating factor and, to a lesser extent, histamine contribute to PE-induced shock. PE induces shock in the absence of the adaptive immune system. LPS contamination is not responsible for PE-induced shock. PE and IgE-mediated mast cell degranulation synergistically induce shock. Tree nuts have similar effects to PE, and skim milk and egg white do not.

CONCLUSION

Peanuts can contribute to shock by causing production of C3a, which stimulates macrophages, basophils, and mast cells to produce platelet-activating factor and histamine.

Cryoglobulinemia and renal disease

PURPOSE OF REVIEW

Cryoglobulinemia occurs in a variety of clinical settings including lymphoproliferative disorders, infection and autoimmune disease. The worldwide pandemic of hepatitis C virus infection has resulted in a significant increase in its extrahepatic complications including cryoglobulinemia and renal disease. Here we review the types of cryoglobulins, mechanisms of cryoglobulin formation, links between hepatitis C virus and renal disease, and current approaches to therapy.

RECENT FINDINGS

The prevalence of cryoglobulinemia in hepatitis C virus-infected individuals is surprisingly large and may be found in more than 50% of some infected subpopulations. Most of these patients will not have overt renal disease, but there is a population of unknown size of patients with subclinical glomerular disease that has the potential to become clinically significant. In cases of hepatitis C virus-associated cryoglobulinemia, treatment remains focused on eradication of viremia, but interventions directed at B lymphocytes are increasingly utilized. The mechanisms of cryoglobulin formation and renal injury remain largely obscure, but recent evidence implicates the innate immune system in the initiation of disease.

SUMMARY

The most common renal injury associated with hepatitis C virus infection, in patients both with and without evidence of cryoglobulinemia, is membranoproliferative glomerulonephritis. There has been increasing focus on defining the mechanisms that link these processes and the evolution of renal injury in all clinical settings of cryoglobulinemia.

Analysis of C4 and the C4 binding protein in the MRL/lpr mouse

Systemic lupus erythematosus is a complement-mediated autoimmune disease. While genetic deficiencies of classical pathway components lead to an increased risk of developing systemic lupus erythematosus, end organ damage is associated with complement activation and immune complex deposition. The role of classical pathway regulators in systemic lupus erythematosus is unknown. C4 binding protein (C4bp) is a major negative regulator of the classical pathway. In order to study the role of C4bp deficiency in an established murine model of lupus nephritis, mice with a targeted deletion in the gene encoding C4bp were backcrossed into the MRL/lpr genetic background. Compared with control MRL/lpr mice, C4bp knockout MLR/lpr mice had similar mortality and similar degrees of lymphoproliferation. There were no differences in the extent of proteinuria or renal inflammation. Staining for complement proteins and immunoglobulins in the kidneys of diseased mice revealed no significant strain differences. Moreover, there was no difference in autoantibody production or in levels of circulating immune complexes. In comparison with C57BL/6 mice, MRL/lpr mice had depressed C4 levels as early as 3 weeks of age. The absence of C4bp did not impact serum C4 levels or alter classical pathway hemolytic activity. Given that immune complex renal injury in the MRL/lpr mouse is independent of Fc receptors as well as the major negative regulator of the classical pathway, new mechanisms for immune-complex-mediated renal injury need to be considered.

Complement in glomerular injury

In recent years, research into the role of complement in the immunopathogenesis of renal disease has broadened our understanding of the fragile balance between the protective and harmful functions of the complement system. Interventions into the complement system in various models of immune-mediated renal disease have resulted in both favourable and unfavourable effects and will allow us to precisely define the level of the complement cascade at which a therapeutic intervention will result in an optimal effect. The discovery of mutations of complement regulatory molecules has established a role of complement in the haemolytic uremic syndrome and membranoproliferative glomerulonephritis, and genotyping for mutations of the complement system are already leaving the research laboratory and have entered clinical practice. These clinical discoveries have resulted in the creation of relevant animal models which may provide crucial information for the development of highly specific therapeutic agents. Research into the role of complement in proteinuria has helped to understand pathways of inflammation which ultimately lead to renal failure irrespective of the underlying renal disease and is of major importance for the majority of renal patients. Complement science is a highly exciting area of translational research and hopefully will result in meaningful therapeutic advances in the near future.

The pathophysiology of HCV induced B-cell clonal disorders

Hepatitis C virus (HCV) has been shown in epidemiologic studies to be associated with immune system disorders. Primarily disorders that stem from B-cell regulatory control disturbance, such as mixed cryoglobulinemia (MC) and non-Hodgkin's lymphoma (NHL). The causative role of HCV in these disorders is supported by the response to anti-viral treatment. The understanding of the pathophysiological process leading from HCV infection to B-cell clonal expansion has improved significantly. Data supports an antigen-driven indirect stimulation of clonal expansion model, leading from oligoclonal to monoclonal expansion and in some instances to frank malignancy. HCV-E2 antigen has been suggested as a candidate antigen as well as NS3. Binding of the B-cell receptor by viral antigens coupled with direct binding of CD-81 by HCV-E2 has been shown to provide a strong proliferative signal. Additional regulatory elements are also affected in HCV-related B-cell clonal expansion, including the Fas and BLyS signaling mechanisms. Finally, genetic events such as bcl-2 rearrangement may also be involved in clonal expansion. In this review, evidence linking HCV with MC and NHL, as well as known events in the pathophysiological process are described.

Emerging Paradigms in the Renal Pathology of Viral Diseases

This review considers recent information that illuminates pathogenetic mechanisms that involve three of the major viral infections that cause renal injury in the form of HIV-associated nephropathy, polyoma virus nephropathy, and hepatitis C virus-associated glomerulonephritis.

The Alternative Pathway of Complement Activation Is Critical for Blister Induction in Experimental Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita is a subepidermal blistering disease associated with tissue-bound and circulating autoantibodies against type VII collagen, a major constituent of the dermal-epidermal junction. The passive transfer of Abs against type VII collagen into mice induces a subepidermal blistering disease dependent upon activation of terminal complement components. To further dissect the role of the different complement activation pathways in this model, we injected C1q-deficient, mannan-binding lectin-deficient, and factor B-deficient mice with rabbit Abs against murine type VII collagen. The development and evolution of blistering had a similar pattern in mannan-binding lectin-deficient and control mice and was initially only marginally less extensive in C1q-deficient mice compared with controls. Importantly, factor B-deficient mice developed a delayed and significantly less severe blistering disease compared with factor B-sufficient mice. A significantly lower neutrophilic infiltration was observed in factor B-deficient mice compared with controls and local reconstitution with granulocytes restored the blistering disease in factor B-deficient mice. Our study provides the first direct evidence for the involvement of the alternative pathway in an autoantibody-induced blistering disease and should facilitate the development of new therapeutic strategies for epidermolysis bullosa acquisita and related autoimmune diseases.

The Many Effects of Complement C3- and C5-Binding Proteins in Renal Injury

The complement system is an important component of the innate immune system and a modulator of adaptive immunity. The entire complement system is focused on C3 and C5. Thus, there are proteins that activate C3 and C5, those that regulate this activation, and those that transduce the effects of C3 and C5 activation products; each can affect the kidney in renal injury. The normal kidney has the inherent capacity to protect itself from complement activation through cellular expression of decay-accelerating factor, membrane cofactor protein (in human beings), and Crry (in rodents). In addition, plasma factor H protects vascular spaces in the kidney. Although the main function of these proteins is to limit complement activation, there is now considerable evidence that they can transduce signals on engagement in immune cells. The G-protein-coupled 7-span transmembrane receptors for C3a and C5a, and the integral membrane complement receptors (CR) for C3b, iC3b, and C3dg, are expressed outside the kidney, particularly in cells of hematopoietic and immune lineage. These are important in renal injury through their infiltration of the kidney and/or by affecting kidney-directed immune responses. There is mounting evidence that intrinsic glomerular and tubular cell C3aR and C5aR expression and activation also can affect renal injury. CR1 on podocytes and the beta2 integrins CR3 and CR4 in kidney dendritic cells have functions that remain poorly defined. Cells of the kidney also have the capacity to produce and activate their own complement proteins. Thus, intrinsic renal cells express decay-accelerating factor, membrane cofactor protein, Crry, C3aR, C5aR, CR1, CR3, and CR4. These can be engaged by C3 and C5 activation products derived from systemic and local pools in renal injury. Given their capacity to provide signals that influence kidney cellular behavior, their activation can have substantial effects in renal injury. Defining these in a cell- and disease-specific fashion is an exciting challenge for future research.

Inhibition of complement factor C5 protects against anti-myeloperoxidase antibody-mediated glomerulonephritis in mice

In mice, administration of murine anti-myeloperoxidase (MPO) IgG induces pauci-immune necrotizing crescentic glomerulonephritis. Recent studies in this model indicate a crucial role for complement activation in disease induction. Here, we investigated the effect of pretreatment or intervention with a C5-inhibiting monoclonal antibody (BB5.1) in the mouse model of anti-MPO IgG-induced glomerulonephritis. Mice received BB5.1 8 h before or 1 day after disease induction with anti-MPO IgG and lipopolysaccharide. Mice were killed after 1 or 7 days. Control antibody-pretreated mice developed hematuria, leukocyturia and albuminuria, and glomerulonephritis with a mean of 21.0+/-8.8% glomerular crescents and 12.8+/-5.5% glomerular capillary necrosis. BB5.1 pretreatment prevented disease development, as evidenced by the absence of urinary abnormalities, a marked reduction in glomerular neutrophil influx at day 1 and normal renal morphology at day 7. Importantly, BB5.1 administration 1 day after disease induction also resulted in a marked attenuation of urinary abnormalities and a more than 80% reduction in glomerular crescent formation. In conclusion, inhibition of C5 activation attenuates disease development in a mouse model of anti-MPO IgG-induced glomerulonephritis. These results favor further investigations into the role of complement activation in human MPO-anti-neutrophil cytoplasmic autoantibody-mediated glomerulonephritis, and indicate that inhibition of C5 activation is a potential therapeutic approach in this disease.

Cryoglobulinaemic vasculitis: classification and clinical and therapeutic aspects

Cryoglobulinaemia may cause cutaneous vasculitis and glomerulonephritis, potentially leading to end stage renal failure. An important proportion of cryoglobulinaemias are secondary to hepatitis C virus infection. Emerging antiviral treatment options offer a chance for causal therapy of these cases of cryoglobulinaemia. This review summarises the classification and clinical and therapeutic aspects of cryoglobulinaemic vasculitis and glomerulonephritis.

Cross-talk between the complement system and endothelial cells in physiologic conditions and in vascular diseases

The endothelial layer represents a continuous physical barrier that controls coagulation and allows selective passage of soluble molecules and circulating cells across the vessel wall into the tissue. The functional activity of the endothelial cells may be influenced by their interaction with components of the complement system. In this review we shall discuss the complex interplay that can be established between the endothelium and complement proteins or activation products. Endothelial cells may also secrete several complement components which contribute to the circulating pool. This process can be regulated by cytokines and other pro-inflammatory stimuli. In addition, complement activation products stimulate endothelial cells to acquire a pro-inflammatory and pro-coagulant status. Expression of regulatory molecules on the cell surface provides protection against an undesired attack by complement activation products. Unrestricted complement activation under pathological conditions may lead to structural and functional changes of the endothelium resulting in vascular disease.