Overexpression of complement inhibitor Crry does not prevent cryoglobulin-associated membranoproliferative glomerulonephritis

Glomerular Diseases Associated With Hepatitis B and C

Infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are prevalent worldwide. In this review, we discuss the epidemiology, pathogenesis, clinical manifestations, and treatment of HBV- and HCV-related glomerulonephritis (GN). The most common histopathologic presentation of HBV-GN is HBV-associated membranous nephropathy, which usually manifests clinically with varying grades of proteinuria and microscopic hematuria. The pathogenesis is likely to be immune complex mediated; however, other host and viral factors have been implicated. The treatment of HBV-GN revolves around antiviral therapy. Various histologic types of glomerular diseases are reported in association with HCV infection, the most frequent being Type 1 membranoproliferative glomerulonephritis, usually in the context of Type 2 mixed cryoglobulinemia. The pathogenesis of HCV-GN can be attributed to glomerular deposition of cryoglobulins or noncryoglobulin-immune complexes. Cryoglobulins typically comprised immunoglobulin Mκ with rheumatoid factor activity. Clinically, patients may present with proteinuria, microscopic hematuria, hypertension, and acute nephritic and/or nephrotic syndrome. The treatment of HCV-GN, especially cryoglobulinemic membranoproliferative glomerulonephritis, encompasses various options including contemporary antiviral therapy with or without conventional and novel immunomodulatory agents.

Costimulatory molecule VSIG4 exclusively expressed on macrophages alleviates renal tubulointerstitial injury in VSIG4 KO mice

BACKGROUND

Activation and infiltration of T cells and macrophages are key features of renal tubulointerstitial injury. The costimulatory molecule V-set and immunoglobulin domain-containing protein-4 (VSIG4), which is exclusively expressed on macrophages, is capable of inhibiting the T cell response. However, it is unclear whether VSIG4 is involved in renal tubulointerstitial injury. This study was designed to investigate the role of VSIG4 in renal tubulointerstitial injury and the related T cell infiltration.

METHODS

The unilateral ureteric obstruction (UUO) model of renal inflammation and tubulointerstitial fibrosis was established in VSIG4 transgenic knock-out C57BL/6 mice (VSIG4(-/-)) and wild-type C57BL/6 mice (VSIG4(+/+)). Comparative analysis of renal biological indices were assessed by quantitative real-time PCR and immunofluorescence staining.

RESULTS

Both the VSIG4(-/-) and VSIG4(+/+) mice showed UUO-related temporal changes in renal expression of CD3, CD4 and CD8 T cell markers, with the protein levels being significantly lower in the VSIG4(+/+) UUO mice. Moreover, at each time point examined the UUO VSIG4(+/+) mice showed significantly lower renal mRNA levels of the cytokines interleukin (IL)-2, interferon- and tumor necrosis factor-, but significantly higher IL-10, than the UUO VSIG4(-/-) mice.

CONCLUSIONS

The macrophage-expressed VSIG4 may act to alleviate renal tubulointerstitial injury via inhibition of T cell infiltration and secretion of inflammation related factors.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

Deletion of activating Fcgamma receptors does not confer protection in murine cryoglobulinemia-associated membranoproliferative glomerulonephritis

Many types of glomerulonephritis are initiated by the deposition of immune complexes, which induce tissue injury via either engagement of Fc receptors on effector cells or via complement activation. Four murine Fcgamma receptors (FcgammaRs) have been identified at present. Ligand binding to FcgammaRI, III, and IV induces cell activation via the immunoreceptor tyrosine-based activation motif on the common gamma chain (FcRgamma). In this study, FcRgamma chain knockout (FcRgamma(-/-)) mice were crossed with thymic stromal lymphopoietin transgenic (TSLPtg) mice, which develop cryoglobulinemic membranoproliferative glomerulonephritis (MPGN). Female mice were studied at 30 and 50 days of age, when MPGN is in early and fully developed stages, respectively. Both TSLPtg and TSLPtg/FcRgamma(-/-) mice developed MPGN with massive glomerular immune deposits, mesangial cell proliferation, extensive mesangial matrix accumulation, and macrophage influx. TSLPtg/FcRgamma(-/-) mice had more glomerular immune complex deposits and higher levels of circulating cryoglobulins, IgG2a, IgG2b, and IgM, compared with TSLPtg mice. TSLPtg and TSLPtg/FcRgamma(-/-) mice developed similar levels of proteinuria. These results demonstrated that deletion of activating FcgammaRs does not confer protection in this model of immune complex-mediated MPGN. The findings contradict accepted paradigms on the role of activating FcgammaRs in promoting features of glomerulonephritis as seen in other model systems. We speculate engagement of FcgammaRs on cells such as monocytes/macrophages may be important for the clearance of deposited immune complexes and extracellular matrix proteins.

Imatinib suppresses cryoglobulinemia and secondary membranoproliferative glomerulonephritis

Imatinib is a receptor tyrosine kinase inhibitor that blocks the activity of c-Abl, c-Kit, and PDGF receptors. We tested the protective effects of imatinib in thymic stromal lymphopoietin transgenic mice, a model of cryoglobulinemia and associated membranoproliferative glomerulonephritis (MPGN), in which some glomerular manifestations likely result from PDGF receptor activation. Surprising, administration of imatinib beginning at weaning suppressed production of cryoglobulin, attenuating both the renal injury and systemic features of cryoglobulinemia. Flow cytometry suggested that inhibition of B cell development in the bone marrow likely caused the reduction in cryoglobulin production. In addition, administration of imatinib to thymic stromal lymphopoietin transgenic mice with established MPGN also diminished cryoglobulin production and reversed the renal and systemic lesions. These data suggest that treatment with imatinib may be a novel therapeutic approach for cryoglobulinemia and MPGN in humans.

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.

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.

Thymic stromal lymphopoietin transgenic mice develop cryoglobulinemia and hepatitis with similarities to human hepatitis C liver disease

Essential mixed cryoglobulinemia in humans is strongly associated with chronic hepatitis C virus infection. It remains controversial whether liver injury in hepatitis C is primarily attributable to direct viral cytopathic effect or to an immune-mediated response. We characterized the role of cryoglobulinemia in the development of liver disease in thymic stromal lymphopoietin (TSLP) transgenic mice that produce mixed cryoglobulinemia and develop hepatitis. The role of immune complexes in this animal model was evaluated using techniques of light, immunofluorescence, and electron microscopy. To assess the role of Fc receptor engagement in mediation of the disease, TSLP transgenic mice were crossbred with mice deficient for immunoglobulin-binding receptor gamma IIb (FcgammaRIIb). Livers from the TSLP transgenic animals showed mild to moderate liver injury, minimal to mild fibrosis, and deposition of immunoglobulin around the portal tracts. TSLP transgenic mice deficient in inhibitory FcgammaRIIb had more severe hepatitis and accelerated mortality. TSLP-associated hepatitis bears strong similarity to hepatitis C virus-related hepatitis as it occurs in humans, making this a valuable model system of chronic hepatitis and fibrosis to study therapies aimed at manipulating immune responses. Periportal immune complex deposition may play an important role in the pathogenesis of hepatitis occurring in the setting of systemic cryoglobulinemia.

Pathogenic mechanisms in membranoproliferative glomerulonephritis

PURPOSE OF REVIEW

This review considers new information on the pathogenesis of a long recognized and poorly understood form of glomerular injury, membranoproliferative glomerulonephritis. This disease has received growing attention as it is the principal renal manifestation of hepatitis C virus infection, which has become pandemic worldwide.

RECENT FINDINGS

This review briefly describes three murine models of membranoproliferative glomerulonephritis suitable for pathogenesis studies. We consider recent evidence implicating innate immune mechanisms in immune and autoimmune-mediated glomerulonephritis, and recent data pointing to the alternative pathway of complement activation in the amplification of glomerulonephritic injury.

SUMMARY

Understanding the contribution of complement activation and innate immunity to the evolution of membranoproliferative glomerulonephritis promises to provide new therapeutic targets for this disease. Inhibitors of the complement cascade are already being tested in clinical trials as therapeutic interventions for some human glomerular diseases. Successful tests of this approach in membranoproliferative glomerulonephritis are still awaited. Our understanding of how the innate immune system modulates glomerulonephritis is still in an early stage, and future studies should be directed at identifying targets and specific interventions that may also benefit patients with this disease.

The Role of Complement in Cryoglobulin-Induced Immune Complex Glomerulonephritis

Many forms of glomerulonephritis are triggered by Ab localization in the glomerulus, but the mechanisms by which this induces glomerular inflammation are not fully understood. In this study we investigated the role of complement in a mouse model of cryoglobulin-induced immune complex glomerulonephritis. Several complement-deficient mice on a C57BL/6 and BALB/c genetic background were used and compared with strain-matched, wild-type controls. Cryoglobulinemia was induced by i.p. injection of 6-19 hybridoma cells producing an IgG3 cryoglobulin with rheumatoid factor activity against IgG2a of allotype a present in BALB/c, but not C57BL/6, mice. Thus, the cryoprecipitate in C57BL/6 mice consisted of the IgG3 cryoglobulin only (type I cryoglobulinemia) compared with IgG3-IgG2a complexes in BALB/c (type II cryoglobulinemia). The survival of mice was not affected by complement deficiency. Glomerular influx of neutrophils was significantly less in C3-, factor B-, and C5-deficient mice compared with wild-type and C1q-deficient mice. It did not correlate with C3 deposition, but did correlate with the amount of C6 deposited. Deficiency of CD59a, the membrane inhibitor of the membrane attack complex, did not induce an increase in neutrophil infiltration, suggesting that the generation of C5a accounts for the effects observed. There was no apparent difference between cryoglobulinemia types I and II regarding the role of complement. Our results suggest that in this model of cryoglobulin-induced glomerulonephritis the neutrophil influx was mediated by C5 activation with the alternative pathway playing a prominent role in its cleavage. Thus, blocking C5 is a potential therapeutic strategy for preventing renal injury in cryoglobulinemia.

Complement and glomerulonephritis: new insights

PURPOSE OF REVIEW

The last few years have seen a huge increase in our understanding of the role of the complement system and its regulation in glomerular disease. Our aim is to summarize the most important advances in this field.

RECENT FINDINGS

The role of complement in systemic lupus erythematosus continues to be elucidated. Classical pathway components protect from the development of autoimmunity, at least in part, through their role in the clearance of apoptotic cells. In contrast, the alternative pathway plays a direct role in exacerbating glomerular injury. Anti-C1q antibodies are related to activity in lupus nephritis and recent studies have shown that they are directly pathogenic in animal models. Proteinuria, whatever the cause, may lead to tubulointerstitial injury and complement activation adds to this process. In particular, deposition of terminal components of complement in the tubular lumen contributes to interstitial myofibroblast activation. There is increasing evidence for the role of complement regulatory proteins in glomerular injury. In particular, abnormalities of factor H or of CD46 may predispose to atypical haemolytic uraemic syndrome. The control proteins also protect against injury in immune complex glomerulonephritis.

SUMMARY

Advances in our understanding of the role of complement in glomerular injury point to the likely therapeutic benefits of targeting the complement system. Many new drugs are becoming available. Careful dissection of the pro and antiinflammatory effects of the complement system which the experimental models allow will assist in designing directed therapy that will avoid the detrimental effects of nonspecific systemic complement inhibition.

Gene expression profiles of peripheral and cord blood mononuclear cells altered by thymic stromal lymphopoietin

Thymic stromal lymphopoietin (TSLP) was reported to induce dendritic cells to produce Th2-attracting chemokines, followed by allergic inflammation through stimulating not only CD4-positive T cells but also CD8-positive T cells. Therefore, in this experiment, GeneChip and hierarchical clustering were applied to screen the molecules in whole immunity triggered by TSLP directly and indirectly using both adult peripheral and cord blood mononuclear cells as well as isolated monocytes. Gene expression profiles screened a variety of molecules that are triggered by TSLP with or without CD40 ligation. In the profile, RNA expressions of indoleamine 2,3-dioxygenase, that is known to induce anergy of T cells and natural killer cells in protecting fetal rejection; many kinds of proteasomes that were reported to trigger cytokine production by inhibiting suppressors of NF-kappaB; and several kinds of chemokines increased, whereas RNA expression of superoxide dismutase 1 decreased, which was unexpected but considered worthy of notice. Expression of chemokines at protein levels and enzymatic activity of indoleamine 2,3-dioxygenase was further confirmed to increase in the presence of TSLP using ELISA and HPLC, respectively. These results suggest that the advent of microarray technology may enable us to screen novel molecular targets to treat TSLP-related allergic inflammation.