Nephritogenic Antigen Research Articles

Mechanisms that potentially contribute to the development of post-streptococcal glomerulonephritis.

Post-streptococcal glomerulonephritis (PSGN) is primarily associated with preceding Group A streptococcal skin or throat infections, now mainly observed in economically disadvantaged communities. This condition significantly predisposes individuals to later-life chronic kidney disease and concurrent renal complications, with the elderly experiencing increased severity and less favourable outcomes. Streptococcal pyrogenic exotoxin B and nephritis associated plasmin receptor are identified nephritogenic antigens (nephritogens). Pathogenesis of PSGN is multifactorial. It can involve the formation of antigen-antibody immune complexes, causing inflammatory damage to renal glomeruli. Deposition of circulating immune complexes or in situ formation of immune complexes in glomeruli, or both, results in glomerulonephritis. Additionally, molecular mimicry is hypothesised as a mechanism, wherein cross-reactivity between anti-streptococcal antibodies and glomerular intrinsic matrix proteins leads to glomerulonephritis. Besides, as observed in clinical studies, streptococcal inhibitor of complement, a streptococcal-secreted protein, can also be associated with PSGN. However, the interplay between these streptococcal antigens in the pathogenesis of PSGN necessitates further investigation. Despite the clinical significance of PSGN, the lack of credible animal models poses challenges in understanding the association between streptococcal antigens and the disease process. This review outlines the postulated mechanisms implicated in the development of PSGN with possible therapeutic approaches.

Bi-specific autoantigen-T cell engagers as targeted immunotherapy for autoreactive B cell depletion in autoimmune diseases.

In autoimmune diseases, autoreactive B cells comprise only the 0.1-0.5% of total circulating B cells. However, current first-line treatments rely on non-specific and general suppression of the immune system, exposing patients to severe side effects. For this reason, identification of targeted therapies for autoimmune diseases is an unmet clinical need. Here, we designed a novel class of immunotherapeutic molecules, Bi-specific AutoAntigen-T cell Engagers (BiAATEs), as a potential approach for targeting the small subset of autoreactive B cells. To test this approach, we focused on a prototype autoimmune disease of the kidney, membranous nephropathy (MN), in which phospholipase A2 receptor (PLA2R) serves as primary nephritogenic antigen. Specifically, we developed a BiAATE consisting of the immunodominant Cysteine-Rich (CysR) domain of PLA2R and the single-chain variable fragment (scFv) of an antibody against the T cell antigen CD3, connected by a small flexible linker. BiAATE creates an immunological synapse between autoreactive B cells bearing an CysR-specific surface Ig+ and T cells. Ex vivo, the BiAATE successfully induced T cell-dependent depletion of PLA2R-specific B cells isolated form MN patients, sparing normal B cells. Systemic administration of BiAATE to mice transgenic for human CD3 reduced anti-PLA2R antibody levels following active immunization with PLA2R. Should this approach be confirmed for other autoimmune diseases, BiAATEs could represent a promising off-the-shelf therapy for precision medicine in virtually all antibody-mediated autoimmune diseases for which the pathogenic autoantigen is known, leading to a paradigm shift in the treatment of these diseases.

Apoptosis in post-streptococcal glomerulonephritis and mechanisms for failed of inflammation resolution.

Post-streptococcal glomerulonephritis is a condition resulting from infection by group A beta-hemolytic streptococcus. The main mechanism involves the formation of immune complexes formed in the circulation or in situ on the glomerular basement membrane, which activates complement and causes various inflammatory processes. Cellular mechanisms have been reported in the induction of kidney damage represented by the infiltration of innate cells (neutrophils and monocyte/macrophages) and adaptive cells (CD4 + lymphocytes and CD8 + lymphocytes) of the immune system. These cells induce kidney damage through various mechanisms. It has been reported that nephritogenic antigens are capable of inducing inflammatory processes early, even before the formation of immune complexes. Usually, this disease progresses towards clinical and renal normalization; however, in a smaller number of patients, it evolves into chronicity and persistent kidney damage. Hypotheses have been proposed regarding the mechanisms underlying this progression to chronicity including failure to induce apoptosis and failure to phagocytose apoptotic cells, allowing these cells to undergo membrane permeabilization and release pro-inflammatory molecules into the environment, thereby perpetuating renal inflammation. Other mechanisms involved include persistent infection, genetic background of the host's complement system, tubulointerstitial changes, and pre-existing kidney damage due to old age and comorbidities.

Autoimmunity in Acute Poststreptococcal GN: A Neglected Aspect of the Disease.

Acute poststreptococcal GN (APSGN) is the prototype of immune complex GN and is associated with manifestations of autoimmune reactivity that have been neglected as epiphenomena. Recently, studies have demonstrated transient antifactor B autoantibodies that activate the alternative complement pathway, bringing self-immunity to a central position in the pathogenesis of APSGN. Therefore, examining other manifestations of autoimmunity that have been reported in association with poststreptococcal GN is of interest. This article reviews the renal and extrarenal manifestations of autoimmune reactivity in APSGN and considers their potential relevance in modifying the usually benign clinical course of the disease. It also discusses related aspects of the nephritogenic antigens, complement activation, and genetic elements associated with immune reactivity and their potential relevance to the familial incidence of the disease.

MON-046 POST-STREPTOCOCCAL ACUTE PULMONARY RENAL SYNDROME

Pulmonary renal syndrome is a group of disorders where we see rapidly progressive glomerulonephritis and diffuse alveolar syndrome. We present a case of post streptococcal pulmonary renal syndrome A 45 year old Sri Lankan Male, dairy farmer by occupation, presented with hemoptysis and increasing shortness of breath for 2 days. His history included a recent travel to Sri Lanka, where he had been unwell 2 weeks preceding the admission with upper respiratory tract symptoms and was given a course of antibiotics. At the time of presentation, his oxygen saturation was low and hence he was started on non-invasive ventilation. His renal function was impaired and urine microscopy showed dysmorphic red cells. Serology for HIV, Hepatitis B and C and Leptospirosis and cultures for TB were all negative. Because of recent history of upper respiratory tract infection, streptococcal antibody titres were done which was significantly positive for both antistreptolysin O titer and Anti DNAase –B, which would be consistent with recent streptococcus pyogenes infection. Antibody screen for anti GBM, ANCA and ANA were negative. CT scan of the chest showed changes consistent with diffuse alveolar haemorrhage and this was confirmed with bronchoscopy ( see below). He underwent a renal biopsy, which was consistent with Post infectious glomerulonephritis (histology below). Given his presentation and worsening respiratory status, Plasma exchange was performed and he was started on pulse methylprednisone. Patient was switched to oral prednisone, which was slowly weaned over 8 weeks and patient made completely recovery both from a respiratory and renal perspective. Discussion: This is an extremely rare case of pulmonary renal syndrome in the setting of post streptococcal pharyngitis. So far, only 5 such cases have been reported. Post streptococcal glomerulonephritis develops approximately 10 days to 2 weeks after streptococcal pharyngitis. It presents with oliguric renal failure, hematuria and hypertension, however most patients present with mild disease. It is very unusual to develop diffuse alveolar haemorrhage to develop in association with PSGN. Mechanism of diffuse alveolar haemorrhage in relation to streptococcal infection is not clear. Possible theory is patients with haemolytic streptococcal infection, the released nephritogenic antigen include nephritis associated plasmin receptor and streptococcal pyrogenic exotoxin B. These antigens accumulate in the glomeruli, trap and maintain the activity of plasmin and induce the degranulation of glomerular basement membrane. The host immunity generates antibody and there is deposition of immune complexes in the sub-epithelial space. A similar process may occur in lung tissue causing diffuse alveolar haemorrhage. Diffuse Alveolar Haemorrhage is a life threatening condition. When pulmonary capillaritis is the pathology of haemorrhage, as in pauci-immune glomerulonephritis or Good Pastures disease, it responds to plasma exchange and pulse intravenous steroids followed by oral steroids. Consistent with this, our patients hemoptysis and respiratory distress completely resolved and renal impairment improved back to normal levels after therapy. Acute pulmonary renal syndrome can occur in the post streptococcal glomerulonephritis. Timely therapy with Plasma exchange and steroids helps in complete resolution.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

CD8+ cells and glomerular crescent formation: outside-in as well as inside-out.

Crescentic glomerulonephritis, a complication of severe immune glomerular injury, is the pathological correlate of rapidly progressive glomerulonephritis, mediated by both humoral and cellular effectors. In the current issue of the JCI, Chen et al. have implicated Bowman's capsule in functionally isolating potentially immune effectors, specifically antigen-specific CD8+ T lymphocytes, from podocytes. They suggest that, in crescentic glomerulonephritis, immune-mediated glomerular endothelial injury results in inside-out injury to the glomerulus, with subsequent leukocyte migration through a weakened or ruptured Bowman's capsule, resulting in outside-in injury. Effector T cells then recognize nephritogenic antigens presented by podocytes or other cells within the urinary space, enhancing injury and crescent formation.

FMS-like tyrosine kinase 3 ligand treatment does not ameliorate experimental rapidly progressive glomerulonephritis.

Fms-like tyrosine kinase 3-ligand (FL) is a growth factor that may expand dendritic cell and regulatory T cell populations. We hypothesised that FL-induced regulatory T cells would protect mice from experimental rapidly progressive glomerulonephritis. To determine if FL was able to enhance regulatory T cell populations, C57BL/6 mice received 10 days of daily intraperitoneal injections of either FL or phosphate buffered saline. To induce accelerated autologous-phase anti-mouse glomerular basement membrane glomerulonephritis, mice were sensitized to sheep globulin 4 days prior to the induction of glomerulonephritis with sheep anti-mouse glomerular basement membrane globulin, and experiments ended 10 days later. FL was administered before, throughout and during the sensitization phase of this glomerulonephritis model. Renal disease and systemic immunity to the nephritogenic antigen were assessed. FL increased regulatory T cell and plasmacytoid dendritic cell proportions within spleen and lymph nodes. FL administration prior to glomerulonephritis did not protect mice from renal injury. When FL was given throughout the model, FL treated mice had reduced survival, with more interstitial neutrophils and glomerular CD11c+ cells than controls. Systemic immune responses showed increased IL-17A production from splenocytes, with more CD11c+ cells, but reduced plasmacytoid dendritic cell proportions in spleen and lymph nodes, despite increased regulatory T cell proportions. Under homeostatic conditions, FL expanded regulatory T cell and plasmacytoid dendritic cell populations, but FL enhanced systemic inflammatory responses and conventional dendritic cell populations when given during experimental glomerulonephritis, suggesting selective attempts to suppress pathogenic immunity by dendritic cell manipulation may be harmful.

A mouse Col4a4 mutation causing Alport glomerulosclerosis with abnormal collagen α3α4α5(IV) trimers

A spontaneous mutation termed bilateral wasting kidneys (bwk) was identified in a colony of NONcNZO recombinant inbred mice. These mice exhibit a rapid increase of urinary albumin at an early age associated with glomerulosclerosis, interstitial nephritis, and tubular atrophy. The mutation was mapped to a location on Chromosome 1 containing the Col4a3 and Col4a4 genes, for which mutations in the human orthologs cause the hereditary nephritis Alport syndrome. DNA sequencing identified a G to A mutation in the conserved GT splice donor of Col4a4 intron 30, resulting in skipping of exon 30 but maintaining the mRNA reading frame. Protein analyses showed that mutant collagen α3α4α5(IV) trimers were secreted and incorporated into the glomerular basement membrane (GBM), but levels were low, and GBM lesions typical of Alport syndrome were observed. Moving the mutation into the more renal damage-prone DBA/2J and 129S1/SvImJ backgrounds revealed differences in albuminuria and its rate of increase, suggesting an interaction between the Col4a4 mutation and modifier genes. This novel mouse model of Alport syndrome is the only one shown to accumulate abnormal collagen α3α4α5(IV) in the GBM, as also found in a subset of Alport patients. These mice will be valuable for testing potential therapies, for understanding abnormal collagen IV structure and assembly, for gaining better insights into the mechanisms leading to Alport syndrome and to the variability in the age of onset and associated phenotypes.

The NLRP3/ASC inflammasome promotes T-cell-dependent immune complex glomerulonephritis by canonical and noncanonical mechanisms

Interleukin (IL)-1β contributes to renal injury in immune complex glomerulonephritis. However, production of mature IL-1β depends on activation of the inflammasome that cleaves pro-IL-1β into its secretable form. A functional role of the NLRP3-containing inflammasome, which responds to various endogenous danger signals, was found in tubulointerstitial nephropathies, but its function in glomerular disease has not been established. To determine whether NLRP3 and its adapter molecule ASC contribute to glomerulonephritis, we induced T-cell-dependent autologous nephrotoxic serum nephritis in Nlrp3- and Asc-deficient mice. Renal expression of NLRP3/ASC inflammasome components and pro-IL-1β increased during nephrotoxic serum nephritis and was abundant in renal dendritic cells. This was associated with renal production of mature IL-1β, indicating inflammasome activation. Nlrp3 and Asc deficiency significantly attenuated glomerular injury, renal leukocyte infiltration, and T-cell activation. Production of mature IL-1β was abrogated in Asc-deficient mice, consistent with a loss of inflammasome-dependent IL-1β activation. Surprisingly, renal IL-1β secretion remained intact in Nlrp3-deficient mice, indicating noncanonical pro-inflammatory effects of NLRP3 in autologous nephrotoxic serum nephritis. This may include NLRP3-mediated glomerular release of pro-inflammatory high-mobility group box 1 protein as a noncanonical function of NLRP3/ASC in glomerulonephritis. Thus, therapeutic blockade of the NLRP3/ASC/IL-1β axis may be beneficial in glomerulonephritis.

The Role of Nephritis-Associated Plasmin Receptor (NAPlr) in Glomerulonephritis Associated with Streptococcal Infection

It is well known that glomerulonephritis can occur after streptococcal infection, which is classically referred to as acute poststreptococcal glomerulonephritis (APSGN). The pathogenic mechanism of APSGN has been described by so-called immune complex theory, which involves glomerular deposition of nephritogenic streptococcal antigen and subsequent formation of immune complexes in situ and/or the deposition of circulating antigen-antibody complexes. However, the exact entity of the causative antigen has remained a matter of debate. We isolated a nephritogenic antigen for APSGN from the cytoplasmic fractions of group A streptococcus (GAS) depending on the affinity for IgG of APSGN patients. The amino acid and the nucleotide sequences of the isolated protein revealed to be highly identical to those of reported plasmin(ogen) receptor of GAS. Thus, we termed this antigen nephritis-associated plasmin receptor (NAPlr). Immunofluorescence staining of the renal biopsy tissues with anti-NAPlr antibody revealed glomerular NAPlr deposition in essentially all patients with early-phase APSGN. Furthermore, glomerular plasmin activity was detected by in situ zymography in the distribution almost identical to NAPlr deposition in renal biopsy tissues of APSGN patients. These data suggest that NAPlr has a direct, nonimmunologic function as a plasmin receptor and may contribute to the pathogenesis of APSGN by maintaining plasmin activity.

The IL-27 Receptor Has Biphasic Effects in Crescentic Glomerulonephritis Mediated Through Th1 Responses

Despite its initially defined role as a T-helper type 1 cell (Th1)-inducing cytokine, interleukin-27 (IL-27) has complex roles in vivo. The role of IL-27 receptor (IL-27R) was defined in experimental crescentic glomerulonephritis induced by a foreign antigen, sheep globulin, which is planted in glomeruli. This lesion is dependent on a Th1 effector cellular response. Twenty-one days after the administration of sheep anti-mouse glomerular basement membrane antibody, wild-type mice developed histologic and functional inflammatory renal injury. Injury was attenuated in the absence of IL-27R α chain (IL-27Rα), the unique component of the IL-27R complex. In contrast to the attenuated renal injury on day 21, Il27ra(-/-) mice exhibited enhanced systemic immune responses, including Th1 responses, with increased IL-2-dependent interferon-γ (IFN-γ) production. However, earlier in the development of the nephritogenic immune response, IFN-γ production was decreased, with reduced early immune responses translating into attenuated renal injury. Having demonstrated decreased early Th1 systemic immune responses, followed by enhanced nephritogenic Th1 immune responses, renal injury was studied at later time points. On days 28 and 35 after injection of the nephritogenic antigen, renal injury was enhanced in Il27ra(-/-) mice compared with wild-type mice in an at least partially IFN-γ-dependent manner. In Th1-dependent autoinflammatory lesions, IL-27Rα has a biphasic role in vivo, initially pathogenic, but ultimately playing a protective role by regulating immune responses and attenuating disease.

Post-streptococcal acute glomerulonephritis in children: clinical features and pathogenesis

Post-streptococcal acute glomerulonephritis (PSAGN) is one of the most important and intriguing conditions in the discipline of pediatric nephrology. Although the eventual outcome is excellent in most cases, PSAGN remains an important cause of acute renal failure and hospitalization for children in both developed and underdeveloped areas. The purpose of this review is to describe both the typical and less common clinical features of PSAGN, to outline the changes in the epidemiology of PSAGN over the past 50 years, and to explore studies on the pathogenesis of the condition with an emphasis on the search for the elusive nephritogenic antigen.

Localization of nephritis-associated plasmin receptor in acute poststreptococcal glomerulonephritis

The nephritis-associated plasmin receptor is a recently identified nephritogenic antigen associated with acute poststreptococcal glomerulonephritis and proposed to play a pathogenic role, but its precise glomerular localization in acute poststreptococcal glomerulonephritis has not been elucidated. We therefore analyzed renal biopsy sections from 10 acute poststreptococcal glomerulonephritis patients by using immunofluorescence staining with anti-nephritis-associated plasmin receptor antibody and various markers of glomerular components. Nephritis-associated plasmin receptor was detected in the glomeruli of all patients, and double staining for nephritis-associated plasmin receptor and collagen IV showed nephritis-associated plasmin receptor to be predominantly on the inner side of the glomerular tufts. Nephritis-associated plasmin receptor-positive areas within glomerular tufts were further characterized with markers for neutrophils, mesangial cells, endothelial cells, and macrophages. In 6 of the patients, nephritis-associated plasmin receptor staining was seen mainly in neutrophils and to a lesser degree in mesangial and endothelial cells. In the other 4 patients, nephritis-associated plasmin receptor staining was seen mainly in mesangial cells and to a lesser degree in neutrophils and endothelial cells. In all patients, macrophages showed little staining. Elevated plasmin activity in glomerular neutrophils was identified by combining in situ zymography staining for plasmin activity and immunofluorescence staining for neutrophils. The glomerular localizations of nephritis-associated plasmin receptor and another nephritogenic antigen, streptococcal pyrogenic exotoxin B, were compared by double immunofluorescence staining and found to be similar. These findings indicate the nephritogenic potential of nephritis-associated plasmin receptor and offer valuable information with respect to the pathogenic mechanism of acute poststreptococcal glomerulonephritis.

Acute interstitial nephritis

Acute interstitial nephritis (AIN) represents a frequent cause of acute kidney injury, accounting for 15-27% of renal biopsies performed because of this condition. By and large, drug-induced AIN is currently the commonest etiology of AIN, with antimicrobials and nonsteroidal anti-inflammatory drugs being the most frequent offending agents. Pathogenesis is based on an immunologic reaction against endogenous nephritogenic antigens or exogenous antigens processed by tubular cells, with cell-mediated immunity having a major pathogenic role. The characteristic interstitial infiltrates, mostly composed of lymphocytes, macrophages, eosinophils, and plasma cells, experience a rapid transformation into areas of interstitial fibrosis. A significant proportion of AIN has nowadays an oligosymptomatic presentation, although the presence of specific extrarenal symptoms such as fever, skin rash, arthralgias, and peripheral eosinophilia has an important role to orientate clinical diagnosis. Identification and removal of the offending drug are the mainstay of the treatment, but recent studies strongly suggest that early steroid administration (within 7 days after diagnosis) improves the recovery of renal function, decreasing the risk of chronic renal impairment. Delayed steroid treatment, when interstitial fibrosis has taken place, would have a less pronounced or nule therapeutic benefit.

Trafficking of inflammatory macrophages from the kidney to draining lymph nodes during experimental glomerulonephritis.

Macrophage accumulation within the glomerulus and renal interstitium is a prominent feature of most forms of glomerulonephritis, but the fate of these inflammatory cells is unknown. Macrophage trafficking to the draining kidney lymph nodes (KLN) was assessed in a detailed kinetic analysis of accelerated antiglomerular basement membrane (GBM) disease in the rat. Leucocytes draining to KLN via lymphatic vessels were identified within the marginal sinus by MoAb labelling of tissue sections. In anti-GBM disease, there was a significant increase in the weight of the KLN due to both lymphoproliferation within the nodes and increased lymphatic drainage from the inflamed kidney, as evidenced by prominent dilation of the marginal sinus and increased numbers of cells within the sinus. In non-inflamed lymph nodes, few ED1+ macrophages were present within the marginal sinus (3.0 +/- 0.6/100 nucleated cells). However, in anti-GBM disease, macrophages became the major cell type within the dilated marginal sinus of the KLN, as shown by labelling with ED1, ED2 and ED3 MoAbs, peaking at 74 +/- 2.6 ED1+ cells/100 nucleated cells at day 14. These changes were not simply due to systemic antigen administration, since in the axillary lymph node (ALN) there was no obvious dilation of the marginal sinus and macrophages accounted for a maximum of only 15 +/- 4.6 ED1+ cells/100 nucleated cells. In conclusion, this study provides indirect evidence that there is significant trafficking of the renal macrophage infiltrate to the KLN during experimental glomerulonephritis. This may be a mechanism whereby nephritogenic antigens, released as a consequence of the local inflammatory response, may be presented to T and B lymphocytes within lymph nodes, resulting in the amplification of the immune response in glomerulonephritis.

A major pathogenic antigen of Heymann nephritis is present exclusively in the renal proximal tubule brush border--studies with a monoclonal antibody against pronase-digested tubular antigen.

We have isolated a nephritogenic 120-kD antigen from rat renal tubule brush border that induces rat Heymann nephritis. A MoAb that recognized this antigen reacted exclusively with the brush border on indirect immunofluorescence and immunoelectron microscopy. Rabbit antiserum against this antigen also reacted exclusively with the brush border. With the injection of this antiserum, rabbit IgG became detectable along the glomerular basement membrane (GBM) after 3 days. Our 120-kD antigen was shown to have a close relationship with gp330 based on the following: (i) this antigen can induce active Heymann nephritis as gp330; (ii) our MoAb reacted with the immune deposits of nephritic kidneys induced not only by the 120-kD antigen but also by gp330, and conversely, rabbit antiserum against gp330 reacted with those induced by the 120-kD antigen as well as gp330; and (iii) by immunoblotting, polyclonal antibodies against the 120-kD antigen reacted with gp330 and polyclonal antibodies against gp330 reacted with the 120-kD antigen. These observations indicate that antigen present exclusively in the brush border can induce active Heymann nephritis, and the common antigenic determinants shared by brush border and the coated pits of glomerular epithelium may not be a prerequisite to induce nephritis. A more precise relationship between the 120-kD antigen and reported C14 fusion protein or 40-kD alpha 2MRAP remains to be established.

Isolation and characterization of the tubular basement membrane antigen associated with human tubulo-interstitial nephritis

The target antigen, a 54-kD glycoprotein (gp54), reactive with sera from patients with anti-tubular basement membrane (anti-TBM) nephritis, was isolated from collagenase-digested (CD) bovine TBM. The purified gp54 was shown to be non-collagenous by amino acid analysis, and to be a unique basement membrane component by amino-terminal sequencing. The nephritogenicity of gp54 was demonstrated by immunizing strain XIII guineapigs with purified gp54, and producing anti-gp54 antibody and tubulo-interstitial nephritis. Anti-gp54 antibody, affinity-purified from sera of patients with anti-TBM nephritis, bound by immunoblotting to 54-kD and, to a lesser extent, 48-kD components of partially purified human CD-TBM. Indirect immunofluorescence showed that gp54 was present in the basement membrane of proximal tubules of the kidneys of normal human, cow, rabbit, guineapig and Brown-Norway rat but not in Lewis rat. Immunoelectron microscopy revealed localization of gp54 along the interstitial side of the TBM and its association with interstitial collagen fibres. These results indicate that gp54 is the nephritogenic antigen involved in tubulo-interstitial nephritis, and is unique in chemical characteristics and localization in the kidney.

Elevated urinary plasmin activity resistant to 2-antiplasmin in acute poststreptococcal glomerulonephritis

A pathogenic role of intraglomerular plasmin bound to nephritogenic antigen (nephritis-associated plasmin receptor, NAPlr) and resistant to physiologic inhibitors such as alpha(2)-antiplasmin (alpha(2)-AP) has recently been proposed in acute poststreptococcal glomerulonephritis (APSGN). To confirm this concept, we analysed the urinary profile of plasmin cascade in APSGN patients. Urine samples from 10 patients with APSGN, 12 patients with IgA nephropathy (IgAN), 10 patients with streptococcal infection without nephritis (SI) and 10 healthy control subjects were analysed. The alpha(2)-AP-resistant plasmin activity was assessed by a chromogenic assay after alpha(2)-AP was added to each urine sample. Urinary plasminogen activator (PA) and plasmin were further analysed by polyacrylamide gel zymography. Urinary NAPlr was assessed by western blot analysis in selected samples. Urinary alpha(2)-AP-resistant plasmin activity corrected for creatinine concentration (units/g x creatinine) was significantly higher in patients with APSGN (2.99 +/- 0.63) than in patients with IgAN (1.02 +/- 0.20, P < 0.01), SI (0.79 +/- 0.17, P < 0.01), or in healthy control subjects (0.73 +/- 0.18, P < 0.01). This tendency was confirmed by casein gel zymography. However urinary PA activity assessed by plasminogen-casein gel zymography did not differ between groups. NAPlr was detected in the urine of APSGN patients. We found elevated urinary plasmin activity resistant to alpha(2)-AP, which may be due to urinary excretion of NAPlr in patients with APSGN. This result supports the pathogenic role of the NAPlr-plasmin complex in the development of APSGN. Furthermore, alpha(2)-AP-resistant urinary plasmin activity may be useful as a diagnostic marker for APSGN.

T-bet Deficiency Attenuates Renal Injury in Experimental Crescentic Glomerulonephritis

T-bet is a transcription factor that is essential for T helper (Th)1 lineage commitment and optimal IFN-gamma production by CD4(+) T cells. We examined the role of T-bet in the development of experimental crescentic glomerulonephritis, which is induced by Th1-predominant, delayed-type hypersensitivity-like responses directed against a nephritogenic antigen. Anti-glomerular basement membrane (GBM) glomerulonephritis was induced in T-bet(-/-) and wild-type C57BL/6 mice. Compared with wild-type controls, renal injury was attenuated in T-bet(-/-) mice with glomerulonephritis, evidenced by less proteinuria, glomerular crescents, and tubulointerstitial inflammation. Accumulation of glomerular CD4(+) T cells and macrophages was decreased, and was associated with reduced intrarenal expression of the potent Th1 chemoattractants CCL5/RANTES and CXCL9/Mig. Supporting the pro-inflammatory nature of T-bet signaling, assessment of systemic immunity confirmed that T-bet(-/-) mice had a reduction in Th1 immunity. The kinetic profile of T-bet mRNA in wild-type mice supported the hypothesis that T-bet deficiency attenuates renal injury in part by shifting the Th1/Th2 balance away from a Th1 phenotype. Expression of renal and splenic IL-17A, characteristically expressed by the Th17 subset of effector T cells, which have been implicated in the pathogenesis of autoimmune disease, was increased in T-bet(-/-) mice. We conclude that T-bet directs Th1 responses that induce renal injury in experimental crescentic glomerulonephritis.

Streptococcal pyrogenic exotoxin B antibodies in a mouse model of glomerulonephritis

Streptococcal pyrogenic exotoxin B is an extracellular cysteine protease. Only nephritis-associated strains of group A streptococci secrete this protease and this may be involved in the pathogenesis of post-streptococcal glomerulonephritis. Mice were actively immunized with a recombinant protease inactive exotoxin B mutant or passively immunized with exotoxin B antibody. Characteristics of glomerulonephritis were measured using histology, immunoglobulin deposition, complement activation, cell infiltration, and proteinuria. None of the mice given bovine serum albumin or exotoxin A as controls showed any marked changes. Immunoglobulin deposition, complement activation, and leukocyte infiltration occurred only in the glomeruli of exotoxin B-hyperimmunized mice. One particular anti-exotoxin B monoclonal antibody, 10G, was cross-reactive with kidney endothelial cells and it caused kidney injury and proteinuria when infused into mice. This cross-reactivity may be involved in the pathogenesis of glomerulonephritis following group A streptococcal infection.