An acute model for IgA-mediated glomerular inflammation in rats induced by monoclonal polymeric rat IgA antibodies

The complement system in the pathogenesis and progression of kidney diseases: What doesn't kill you makes you older

The Complement System is an evolutionarily conserved component of immunity that plays a key role in host defense against infections and tissue homeostasis. However, the dysfunction of the Complement System can result in tissue damage and inflammation, thereby contributing to the development and progression of various renal diseases, ranging from atypical Hemolytic Uremic Syndrome to glomerulonephritis. Therapeutic interventions targeting the complement system have demonstrated promising results in both preclinical and clinical studies. Currently, several complement inhibitors are being developed for the treatment of complement-mediated renal diseases. This review aims to summarize the most recent insights into complement activation and therapeutic inhibition in renal diseases. Furthermore, it offers potential directions for the future rational use of complement inhibitor drugs in the context of renal diseases.

Targeting complement in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Recent years have witnessed significant improvements in the understanding of the pathogenesis of IgAN and particularly, the pathogenic role of complement activation. The alternative complement pathway is the major complement cascade activator in IgAN, and glomerular C3 deposition has been shown to correlate with disease progression. In addition, several studies have provided insight into the pathogenic role of factor H-related proteins -1 and -5 in IgAN, as independent players in complement dysregulation. The lectin pathway has also been shown to be associated with the severity of IgAN. Glomerular deposition of C4d has been associated with increased histologic disease activity, faster decline in estimated glomerular filtration rate and higher risk of kidney failure. On the other hand, although overlooked in the Oxford classification, numerous studies have shown that the coexistence of thrombotic microangiopathy in IgAN is a significant indicator of a poorer prognosis. All the breakthroughs in the understanding of the contributing role of complement in IgAN have paved the way for the development of new complement-targeted therapies in this disease. Several ongoing trials are evaluating the efficacy of new agents against factor B (iptacopan, Ionis-FB-LRX), C3 (pegcetacoplan), factor D (vemircopan, pelecopan), C5 (ravulizumab, cemdisiran) and C5a receptor 1 (avacopan). In this study, we provide a comprehensive review of the role of complement in IgAN, including the emerging mechanisms of complement activation and the promising potential of complement inhibitors as a viable treatment option for IgAN.

Kidney diseases

Dysregulation and accelerated activation of the alternative pathway (AP) of complement is known to cause or accentuate several pathologic conditions in which kidney injury leads to the appearance of hematuria and proteinuria and ultimately to the development of chronic renal failure. Multiple genetic and acquired defects involving plasma- and membrane-associated proteins are probably necessary to impair the protection of host tissues and to confer a significant predisposition to AP-mediated kidney diseases. This review aims to explore how our current understanding will make it possible to identify the mechanisms that underlie AP-mediated kidney diseases and to discuss the available clinical evidence that supports complement-directed therapies. Although the value of limiting uncontrolled complement activation has long been recognized, incorporating complement-targeted treatments into clinical use has proved challenging. Availability of anti-complement therapy has dramatically transformed the outcome of atypical hemolytic uremic syndrome, one of the most severe kidney diseases. Innovative drugs that directly counteract AP dysregulation have also opened new perspectives for the management of other kidney diseases in which complement activation is involved. However, gained experience indicates that the choice of drug should be tailored to each patient's characteristics, including clinical, histologic, genetic, and biochemical parameters. Successfully treating patients requires further research in the field and close collaboration between clinicians and researchers who have special expertise in the complement system.

Complement activation in IgA nephropathy

IgA nephropathy pathogenesis is incompletely understood, and this limits the development of disease-specific biomarkers and effective therapies. Evidence of complement activity in IgA nephropathy is well established. However, a growing body of research indicates complement activity is an important contributor to IgA nephropathy pathology. In particular, multiple associations have been identified between complement alternative, lectin and terminal pathway proteins and IgA nephropathy severity. Recently, we have also gained insight into possible mechanisms that could link glomerular IgA deposition, complement activity, glomerular inflammation and disease severity. Ongoing clinical trials of therapeutic complement inhibitors will provide insight into the importance of complement activity to IgA nephropathy pathogenesis. Further research into mechanisms of complement activity is essential to improving our understanding and management of patients with IgA nephropathy.

Aberrantly Glycosylated IgA1 in IgA Nephropathy: What We Know and What We Don't Know

IgA nephropathy (IgAN), the most common primary glomerular disease worldwide, is characterized by glomerular deposition of IgA1-containing immune complexes. The IgA1 hinge region (HR) has up to six clustered O-glycans consisting of Ser/Thr-linked N-acetylgalactosamine usually with β1,3-linked galactose and variable sialylation. Circulating levels of IgA1 with abnormally O-glycosylated HR, termed galactose-deficient IgA1 (Gd-IgA1), are increased in patients with IgAN. Current evidence suggests that IgAN is induced by multiple sequential pathogenic steps, and production of aberrantly glycosylated IgA1 is considered the initial step. Thus, the mechanisms of biosynthesis of aberrantly glycosylated IgA1 and the involvement of aberrant glycoforms of IgA1 in disease development have been studied. Furthermore, Gd-IgA1 represents an attractive biomarker for IgAN, and its clinical significance is still being evaluated. To elucidate the pathogenesis of IgAN, it is important to deconvolute the biosynthetic origins of Gd-IgA1 and characterize the pathogenic IgA1 HR O-glycoform(s), including the glycan structures and their sites of attachment. These efforts will likely lead to development of new biomarkers. Here, we review the IgA1 HR O-glycosylation in general and the role of aberrantly glycosylated IgA1 in the pathogenesis of IgAN in particular.

Current Trends on Glomerulosclerosis Regression

The role of the renin-angiotensin system in hypertension and end-organ damage has long been recognized. Angiotensin l converting enzyme inhibitors are superior to other antihypertensive agents in protecting the kidney against progressive deterioration, even in normotensive persons. Likewise, angiotensin II type 1 receptor antagonists improve or even reverse glomerulosclerosis in rat animal models. These findings suggest that Angiotensin II has nonhemodynamic effects in progressive renal disease. The renin-angiotensin system is now recognized to be linked to the induction of plasminogen activator-inhibitor-1, possibly via the AT4 receptor, thus promoting both thrombosis and fibrosis. Interactions of the renin-angiotensin system with aldosterone and bradykinin may impact both blood pressure and tissue injury. The beneficial effect on renal fibrosis of inhibiting the renin-angiotensin system likely reflects the central role that angiotensin has in regulating renal function and structure by its various actions. This article explores the renin-angiotensin-aldosterone system with plasminogen activator-inhibitor-1 interaction and the potential significance of these interactions in the pathogenesis of progressive renal disease and remodeling of renal sclerosis.

Predictive value of mesangial C3 and C4d deposition in IgA nephropathy

We aimed to determine the relative contribution of each complement (C3 and C4d) deposition to the progression of IgA nephropathy (IgAN). We enrolled a total of 380 patients with biopsy-confirmed IgAN. Mesangial deposition of C3(<2+ vs. ≥2+) and C4d(positive vs. negative) was evaluated by immunofluorescence staining and immunohistochemistry, respectively. Study endpoint was the composite of a 30% decline in eGFR or ESRD. The risk of reaching the primary outcome was significantly higher in patients having C3 ≥ 2+ and C4d(+) than in corresponding counterparts. Adding C3 deposition to clinical data acquired at kidney biopsy modestly increased the area under the receiver-operating characteristic curve, net reclassification improvement, and integrated discrimination improvement (IDI); adding C4d increased IDI only. In conclusion, mesangial C3 and C4d deposition was an independent risk factor for progression of IgAN. C3 showed better predictability than C4d, suggesting that lectin pathway alone has limited clinical prognostic value.

Circulating complement factor H-related proteins 1 and 5 correlate with disease activity in IgA nephropathy

IgA nephropathy (IgAN) is a common cause of chronic kidney disease and end-stage renal failure, especially in young people. Due to a wide range of clinical outcomes and difficulty in predicting response to immunosuppression, we need to understand why and identify which patients with IgAN will develop progressive renal impairment. A deletion polymorphism affecting the genes encoding the complement factor H-related protein (FHR)-1 and FHR-3 is robustly associated with protection against IgAN. Some FHR proteins, including FHR-1 and FHR-5, antagonize the ability of complement factor H (fH), the major negative regulator of the complement alternative pathway, to inhibit complement activation on surfaces, a process termed fH deregulation. From a large cohort of patients, we demonstrated that plasma FHR-1 and the FHR-1/fH ratio were elevated in IgAN and associated with progressive disease. Plasma FHR-1 negatively correlated with eGFR but remained elevated in patients with IgAN with normal eGFR. Serum FHR5 was slightly elevated in IgAN but did not correlate with eGFR. Neither FHR5 levels nor the FHR-5/fH ratio was associated with progressive disease. However, higher serum FHR-5 levels were associated with a lack of response to immunosuppression, the presence of endocapillary hypercellularity, and histology scores of disease severity (the Oxford Classification MEST score). Thus, FHR-1 and FHR-5 have a role in IgAN disease progression.

Decreased Serum C3 Levels in Immunoglobulin A (IgA) Nephropathy with Chronic Kidney Disease: A Propensity Score Matching Study

Background

The effects of low serum C3 levels and the activation of the complement system on the development and the prognosis of IgAN are unclear. The present study aimed to determine whether decreased levels of complement C3 influence the prognosis of IgAN patients with chronic kidney disease.

Material/Methods

We enrolled a total of 1564 patients with primary IgAN diagnosed by renal biopsy at the Chinese PLA General Hospital from January 2011 to March 2015. The endpoint was end-stage renal disease (ESRD) or a doubling of the baseline serum creatinine (D-SCr) level. All patients were using 1: 1 propensity score matching (PSM), and the baseline values were not significantly different between these 2 groups (P>0.05).

Results

During a follow-up period, 14 patients in the group with decreased C3 levels reached the endpoint, with 12 patients with normal C3 levels. There was no significant difference between the 2 groups in achieving D-SCr or ESRD (P=0.676). In multivariate Cox analysis, adjusted for demographic and laboratory examination, the risk of reaching the endpoint was comparable in the 2 groups (HR, 0.70; 95% CI, 0.27–1.78; P=0.449;). Furthermore, the risk of reaching ESRD (HR, 0.83; 95% CI, 0.25–2.75; P=0.757) and D-SCr (HR, 1.45; 95% CI, 0.20–10.60; P=0.718) did not differ between the 2 groups.

Conclusions

Decreased serum C3 levels in IgA nephropathy with chronic kidney disease did not play a decisive role in renal progression.

Nationwide epidemiological survey of childhood IgA vasculitis associated hospitalization in the USA

At the national level, IgA vasculitis-related hospitalizations among children in the USA are scarce. Furthermore, nationwide epidemiology and hospital course of children with IgA vasculitis have not been fully described in the USA, and disparities by race/ethnicity remain unknown. Hospital discharge records of patients aged 19 years or younger were obtained from the 2003, 2006, 2009, and 2012 Kids' Inpatient Database, and they were weighted to estimate the annual hospitalization rates with respect to age, gender, and race/ethnicity in the USA. Annual hospitalization rates were calculated using weighted case estimates and US census data. Negative binomial regression was used to ascertain the factors associated with length of hospital stay. Total annual hospitalization rates showed a significant decreasing trend, ranging from 2.45 per 100,000 children in 2003 to 1.89 per 100,000 children in 2012 (p < 0.001). The peak ages of the hospitalized children with IgA vasculitis were 2 and 7 years, and male-to-female ratios were 1.38-1.44. Factors associated with length of hospital stay were patients' ages (10-14 and 15-19 years), race/ethnicity (Hispanic, Asian, and Pacific Islander), comorbid electrolyte abnormality, GI hemorrhage, intussusception, renal symptoms, and GI symptoms. The annual hospitalization rates for IgA vasculitis are declining in the USA across multiple age groups. GI and renal manifestations are associated with increased length of hospital stay.

Decreased circulating C3 levels and mesangial C3 deposition predict renal outcome in patients with IgA nephropathy

BACKGROUND AND AIMS

Mesangial C3 deposition is frequently observed in patients with IgA nephropathy (IgAN). However, the role of complement in the pathogenesis or progression of IgAN is uncertain. In this observational cohort study, we aimed to identify the clinical implications of circulating C3 levels and mesangial C3 deposition and to investigate their utility as predictors of renal outcomes in patients with IgAN.

METHODS

A total of 343 patients with biopsy-proven IgAN were enrolled between January 2000 and December 2008. Decreased serum C3 level (hypoC3) was defined as C3 <90 mg/dl. The study endpoint was end-stage renal disease (ESRD) and a doubling of the baseline serum creatinine (D-SCr).

RESULTS

Of the patients, there were 66 patients (19.2%) with hypoC3. During a mean follow-up of 53.7 months, ESRD occurred in 5 patients (7.6%) with hypoC3 compared with 9 patients (3.2%) with normal C3 levels (P = 0.11). However, 12 patients (18.2%) with hypoC3 reached D-SCr compared with 17 patients (6.1%) with normal C3 levels [Hazard ratio (HR), 3.59; 95% confidence interval (CI), 1.33-10.36; P = 0.018]. In a multivariable model in which serum C3 levels were treated as a continuous variable, hypoC3 significantly predicted renal outcome of D-SCr (per 1 mg/dl increase of C3; HR, 0.95; 95% CI, 0.92-0.99; P = 0.011). The risk of reaching renal outcome was significantly higher in patients with mesangial C3 deposition 2+ to 3+ than in patients without deposition (HR 9.37; 95% CI, 1.10-80.26; P = 0.04).

CONCLUSIONS

This study showed that hypoC3 and mesangial C3 deposition were independent risk factors for progression, suggesting that complement activation may play a pathogenic role in patients with IgAN.

Thy-1 Expressing Mesenchymal Cells in Rat Nephrogenesis in Correlation with Cells Immunoreactive for α-Smooth Muscle Actin and Vimentin

Thy-1 expression may influence myofibroblast development. Through the epithelial-mesenchymal transition (EMT), injured renal epithelial cells undergo regression to the metanephric mesenchymal phenotype and then acquire a myofibroblastic nature (expressing α-smooth muscle actin; α-SMA). Because the metanephric blastema differentiates into mesenchymal and renal epithelial cells, we investigated Thy-1 immunoexpression during nephrogenesis in F344 rats in correlation with vimentin and α-SMA expressions. Kidney samples were obtained from fetuses on gestation days 18 and 21, neonates on days 1-18 and adults at 6 weeks of age. Mesangial cells in S-shaped bodies and immature and mature glomeruli continuously expressed both Thy-1 and α-SMA during early nephrogenesis (fetuses and neonates on days 1-9). During early nephrogenesis, loosely-arranged blastemal cell-derived mesenchymal cells in the cortex and medulla also exhibited Thy-1 and α-SMA, although the α-SMA expression was weaker than that of Thy-1. Vimentin expression coincided with that of Thy-1. These findings indicate that the derivation of α-SMA-expressing myofibroblastic cells may be related to mesangial or blastemal cells expressing both Thy-1 and α-SMA. Interestingly, there was a difference in Thy-1 expression between cortical and medullary tubulointerstitial cells from late nephrogenesis (neonates on days 12-18) and those from adults in that the cortical cells reacted faintly or negatively to Thy-1, whereas the medullary cells reacted strongly to Thy-1; additionally, bundle-arranged mesenchymal cells that were only observed in the neonates on days 1-12 reacted strongly to α-SMA, but faintly to Thy-1. Blastemal cell-derived mesenchymal cells seem to alter the immunoexpressions of Thy-1 and α-SMA, depending on the conditions which they develop. Thy-1 immunoexpression would be useful for investigation of reverse embryogenesis, which might occur in fibrotic kidneys.

Immunopathogenesis of IgAN

The defining hallmark of IgA nephropathy (IgAN) is deposition of polymeric IgA1 in the glomerular mesangium accompanied by a mesangial proliferative glomerulonephritis. The mechanisms involved in mesangial polymeric IgA1 deposition and the initiation of inflammatory glomerular injury remain unclear. This lack of a complete understanding of the pathogenesis of IgAN has meant that there is still no treatment known to modify mesangial deposition of IgA. Increasing evidence, however, supports the importance of IgA-containing immune complex formation as a pivotal factor driving mesangial IgA deposition and triggering of glomerular injury. A number of potentially important changes to the IgA1 molecule have been identified in IgAN, which may contribute to immune complex formation. These changes suggest that the polymeric IgA1 that deposits in IgA nephropathy is derived from mucosally primed plasma cells. The presence of this IgA in the circulation reflects displacement of mucosal B lineage cells to systemic sites and may be the result of mishoming of lymphocytes trafficking along the mucosa-bone marrow axis.

Henoch Schonlein purpura in childhood: epidemiological and clinical analysis of 150 cases over a 5-year period and review of literature

OBJECTIVE

To examine epidemiological, clinical, and outcome in Italian children affected with Henoch Schönlein purpura (HSP).

METHODS

Retrospective study of children discharged with a diagnosis of HSP from the Meyer Children's Hospital, between 1998 and 2002. Epidemiological, clinical, laboratory data, treatment, and outcome were collected by reviewing medical charts. One year after data collection, the children's parents were interviewed by telephone about the outcome.

RESULTS

150 children entered the study: M:F=1.8:1; mean age 6.1+/-2.7 years. At onset, purpura was present in all cases, arthritis/arthralgias in 74%, abdominal involvement in 51%, scrotal edema in 13%, renal involvement in 54%, severe nephropathy in 7%, acute renal insufficiency in 2%, and intussusception in 0.6%. Purpura was the presenting symptom in 74%, arthritis in 15%, and abdominal pain in 12%. The most frequent laboratory abnormalities were high-erythrocyte sedimentation rate (ESR) (57%), hyper-IgA (37%), and proteinuria (42%). All patients recovered within 2 months. Recurrences, verified in 35%, were correlated with high ESR values and corticosteroid (CS) treatment, independently from other variables. After a mean 2.5-years follow-up, 2 patients had hematuria with normal renal function.

CONCLUSION

Epidemiological and clinical findings in our cohort are similar to those in the literature, even though the mean disease duration was shorter than previously reported. Relapses occurred significantly more frequently in children treated with CS. This finding supports the recommendation to limit the use of steroids to a carefully selected group of HSP children. The prognosis was excellent; although severe nephropathy was found in a small percentage of the children, at follow-up all had normal renal function. Thus, our study confirms the benignity of HSP in Italian children, especially regarding renal outcome.

Back-pack mice as a model of renal mesangial IgA dimers deposition

Mesangial IgA in IgA nephropathy are dimers with a J chain but no poly-Ig receptor. This molecular structure has led to the hypothesis that these IgA are issued from the lamina propria of mucosal areas, reaching the kidney by way of the peripheral blood. The availability of hybridomas producing IgA dimers provided an opportunity to test this hypothesis in a new experimental model of IgA nephropathy. Mice were injected subcutaneously (back-pack mice) or intraperitoneally with hybridoma cells secreting either monoclonal IgA dimers, or monoclonal IgA monomers. The influence of immune complex formation was also tested in both these models. Renal IgA deposition was investigated 12 days after the injection of hybridoma cells. Backpack mice developed highly vascularized subcutaneous tumors. Mesangial IgA deposits were observed only in dimeric IgA hybridoma back-pack animals. No significant staining was observed in glomeruli from animals injected with hybridoma cells producing monomeric IgA. None of the hybridomas induced mesangial deposition when injected intraperitoneally. This animal model demonstrates the capacity of circulating IgA dimers to spontaneously form mesangial deposits and contributes to confirm the involvement of abnormalities of mucosal immunity in the pathogenesis of IgA nephropathy.

Pathogenesis of IgA nephropathy

In IgA nephropathy (IgAN), there is dysregulation of the IgA response to a wide range of antigens. The dysregulation promotes synthesis of polymeric IgA1 (pIgA1) with physicochemical characteristics that favor mesangial deposition, including altered O-glycosylation of the hinge region. This may be the synthesis of IgA in the systemic compartment, which has the phenotype of mucosal IgA. There is not a change in IgA1 structure to an entirely abnormal form; rather, there is a shift that results in a proportional increase in forms of IgA1 also found in healthy individuals. Altered O-glycosylation could favor pIgA1 deposition by promoting formation of macromolecular IgA and immune complexes. Mesangial injury follows through interactions of pIgA1 with the cells and extracellular matrix proteins of the mesangium and the activation of complement. The final clinical expression of IgAN also depends on generic factors, including hypertension and proteinuria, and a fibrotic renal response. No single "IgAN gene" has been identified, and it is likely that multiple interacting genes will eventually prove to underlie susceptibility to IgAN and the risk of progressive renal disease. These new pathogenic insights have not yet led to new therapeutic opportunities.

Combined glomerular deposition of polymeric rat IgA and IgG aggravates renal inflammation

BACKGROUND

IgA nephropathy (IgAN) is characterized by deposition in the glomerular mesangium of IgA together with C3, C5b-9, and properdin. IgG deposition as a risk factor in IgAN was recently confirmed by a long-term follow-up of patients with IgAN. We previously reported on an acute model of IgA-mediated glomerular inflammation in Wistar rats.

METHODS

To investigate the effect of the combination of IgA and IgG on glomerular injury, Wistar rats were injected with a minimum dose of rat IgG in the presence or absence of a subnephritogenic dose of polymeric rat IgA. Subsequently, glomerular complement activation, influx of inflammatory cells, proteinuria, and hematuria were assessed.

RESULTS

Administration of IgG to the rats resulted in maximal proteinuria of 20.3 +/- 12.1 mg/24 h on day 2 and an absence of overt glomerular inflammation. Administration of polymeric rat IgA antibodies to rats resulted in hematuria with a moderate mesangial complement deposition. In the combination group, however, glomerular deposition of C5b-9 was dramatically increased. This was accompanied by increased proteinuria as compared with rats receiving IgA or IgG antibody injections alone on day 7. Microhematuria occurred in rats receiving either polymeric rat IgA or IgG alone or the combination. While both rat IgG and polymeric IgA induced minor mesangial cell (MC) proliferation and MC lysis, the combination resulted in a pronounced, significant increased percentage of aneurysm formation on day 7 after injection.

CONCLUSIONS

We conclude that in this model of IgA-induced glomerulopathy, a selective, complement-dependent glomerular inflammation is induced in Wistar rats by glomerular codeposition of rat isotypic monoclonal antibodies.

Bone marrow transplantation attenuates murine IgA nephropathy: role of a stem cell disorder

BACKGROUND

The pathogenesis of IgA nephropathy is still obscure. The aim of this study was to investigate whether the fundamental pathogenesis of IgA nephropathy lies in bone marrow stem cells (BMCs).

METHODS

We used donors of two different strains for bone marrow transplantation (BMT) into mice with a high content of serum IgA (ddY strain, HIGA mice), a murine model of IgA nephropathy. One group (B6-->HIGA, N = 5) received BMCs of C57BL/6j (B6) mice, and the other (HIGA-->HIGA, N = 8) were reconstituted with BMCs of HIGA mice.

RESULTS

Twenty-six weeks after BMT, in B6-->HIGA mice, mesangial deposits of IgA and C3 were statistically milder than those in HIGA-->HIGA mice. Light microscopic observations disclosed that glomerular sclerosis and mesangial matrix expansion in B6-->HIGA mice were decreased compared with those in HIGA-->HIGA mice. These B6-->HIGA mice also excreted less urinary albumin than HIGA-->HIGA mice. Furthermore, serum levels of IgA in B6-->HIGA mice were markedly lower than those in HIGA-->HIGA mice. Size analysis of serum IgA revealed that macromolecular IgA were notably lower in B6-->HIGA mice than in HIGA-->HIGA mice.

CONCLUSIONS

Our results suggest that qualitative and quantitative changes of serum IgA are determined at the level of stem cells, and that BMT from normal donors can attenuate glomerular lesions in HIGA mice. This approach may offer a new avenue to study the pathogenesis of IgA nephropathy.

Experimental murine IgA nephropathy following passive administration of vomitoxin-induced IgA monoclonal antibodies

Oral exposure of mice to vomitoxin (VT) induces elevated levels of serum IgA, circulating IgA immune complexes (IgA-IC), mesangial IgA deposition and haematuria, which all mimic the clinical signs of human IgA nephropathy (IgAN). To further assess the effects of VT-induced IgA in the murine model, B6C3F1 and BALB/C mice were injected intraperitoneally with affinity-purified monoclonal IgA derived from Peyer's patch hybridomas of VT-exposed mice. In B6C3F1 mice, serum IgA, IgM and IgA-IC levels were increased two- to fivefold in treatment groups after 4 and 6 wk compared with controls, whereas increases in serum IgG as high as 18-fold were observed. Urinary erythrocyte counts were also significantly elevated in treatment groups after 2, 4 and 6 wk compared with controls. Concurrent increases in IgA and IgG complexes containing casein, the dietary protein source, occurred in treatment mice. Mesangial IgA, IgG, IgM and C3 deposition were significantly increased in all treatment mice after 6 wk. Electron-dense deposits occurred in the glomeruli of IgA-injected mice after 6 wk. All the above parameters were similarly affected in BALB/C mice. Injection of IgA-secreting hybridoma cells into BALB/C mice increased serum IgA, IgA-IC and IgG levels as well as elevated mesangial IgA, IgG and C3 deposition and haematuria after 2-3 weeks compared with controls. In total, these data indicate that passive administration of VT-induced IgAs can induce the hallmarks of IgA nephropathy. Casein, an antigen found in the diet used for these mice, appeared to form IC with IgA or IgG and these IC may participate in the pathogenesis of this nephropathy.

Evidence suggesting the involvement of hematopoietic stem cells in the pathogenesis of IgA nephropathy

To investigate the role of hematopoietic stem cells in the pathogenesis of IgA nephropathy, T-cell-depleted bone marrow cells for IgA nephropathy-prone ddY mice were transplanted into C57BL/6j (B6) mice pretreated with cyclophosphamide. In the 12th week after bone marrow transplantation, transplanted bone marrow cells had successfully regenerated. In B6 recipients of T-cell-depleted allogeneic bone marrow cells for ddY mice ([ddy-->B6]), mesangial IgA and C3 deposits were significantly more intense than those in B6 mice receiving syngeneic bone marrow cells of B6 mice ([B6-->B6]). The serum IgA level in [ddY-->B6] mice was higher than that in [B6-->B6] mice. Molecular profile analysis of serum IgA revealed that the serum concentration of macromolecular IgA was increased in [ddY-->B6], but not in [B6-->B6] mice. These data suggest that disorders programmed at the level of BMCs are involved in the pathogenesis of IgA nephropathy by increasing circulating levels of macromolecular IgA.

Anti-C1q receptor/calreticulin autoantibodies in patients with systemic lupus erythematosus (SLE)

SLE is a disease characterized by the presence of multiple autoantibodies and high levels of circulating immune complexes. We studied the presence and functional relevance of autoantibodies directed against a receptor for the collagen-like stalks of the first subcomponent of complement, also known as calreticulin (cC1qR/CaR), in patients with SLE. In a cross-sectional study it was found that higher titres of antibodies against cC1qR/CaR are present in sera of SLE patients compared with normal donors. No association between anti-cC1qR/CaR titres and SLE disease activity was found. Following gel filtration of SLE serum it was found that anti-cC1qR/CaR reactivity is associated with the peak of monomeric IgG. Purified IgG from patients was able to specifically immunoprecipitate cC1qR/CaR. Since we have shown previously that cC1qR/CaR is able to inhibit the haemolytic activity of Clq, we determined a possible pathogenic role for anti-cC1qR/CaR on complement regulation. IgG derived from SLE serum reversed the inhibitory capacity of cC1qR/CaR in a dose-dependent fashion up to 63%, whereas IgG from normal donors had no significant effect. With respect to the capacity of anti-cC1qR/CaR antibodies to activate neutrophils, it was found that incubation of normal neutrophils with F(ab')2 anti-cC1qR/CaR resulted in a very limited oxidative burst. However, cross-linking of F(ab')2 anti-cC1qR/CaR on the neutrophils clearly induced neutrophil activation. Pre-incubation of the SLE-derived F(ab')2 with cC1qR/CaR prevented activation of neutrophils up to 81+/-5%. These results suggest that the presence of anti-cC1qR/CaR antibodies in patients with SLE may modulate complement and neutrophil activation.

Activated complement C3: a potentially novel predictor of progressive IgA nephropathy

In the search for a serologic marker of disease activity, we measured concentrations of activated C3 (actC3, that is, neoantigens developing after C3 activation on breakdown products), C4-C3 complexes and soluble C5b-9 (sC5b-9) in one or two plasma samples from adult patients with IgA nephropathy (IgAN, N = 50) or Henoch-Schönlein purpura (HSP, N = 4). As controls, 20 patients with non-immune renal disease, but comparable age, degree of proteinuria, renal dysfunction and prevalence of hypertension were studied. Compared to controls, actC3 levels were elevated in 30% of the patients with IgAN and one of the HSP patients. C4-C3 complexes were elevated in only 8% of the IgAN patients, and sC5b-9 levels were within the control range in all IgAN and HSP patients. In IgAN patients with elevated actC3 levels, proteinuria and hematuria were more pronounced than in those with normal levels. Elevated plasma concentrations of actC3 at the first presentation correlated with subsequent deterioration of renal function both in patients with initially normal and already impaired renal function (r = -0.56, N = 44, P = 0.003). The five IgAN patients with elevated actC3 on both occasions of obtaining plasma showed the most rapid loss of renal function. We conclude that mainly alternative pathway complement activation can be demonstrated in patients with IgAN and HSP. In IgAN patients the presence of complement activation is associated with more severe renal disease. Further studies are warranted to examine the clinical usefulness of actC3 as a predictor of the subsequent course of IgAN.

Induction of microhematuria by an IgA isotype switch variant of a monoclonal anti-Thy-1.1 antibody in the rat

IgA nephropathy (IgAN) is a chronic form of glomerulonephritis (GN) characterized by the deposition in the glomerular mesangium of mainly IgA. An experimental form of mesangial proliferative GN can be induced in rats by either polyclonal or monoclonal antibodies against Thy-1.1, a glycoprotein present on the surface of MC. The IgG-mediated renal inflammation is complement dependent and associated with influx of platelets and monocytes. In the present study we switched an IgG2a anti-Thy-1.1 (ER4G) producing hybridoma to an IgA anti-Thy-1.1 (ER4A) producing clone and analyzed the effects of IgA anti-Thy-1.1 in rats. FPLC analysis by gel filtration revealed that the IgA produced by the hybridoma cells was mainly dimeric and polymeric. Infusion of rats with purified ER4A (1 mg/kg) resulted in the deposition of IgA in a mesangial pattern in the glomeruli, similar to that found with ER4G. While administration of ER4G resulted in proteinuria, no significant urinary protein excretion was found in rats treated with ER4A. However, significant microhematuria was observed in rats receiving either ER4A or ER4G. Furthermore, the administration of ER4A was not accompanied by activation of complement, and no significant influx of monocytes or polymorphonuclear leukocytes was observed in contrast to the rats receiving ER4G. We conclude that microhematuria is selectively induced in Wistar rats by mouse IgA anti-Thy-1.1 without detectable complement-mediated injury to MC. These studies may be of importance in understanding the mechanisms leading to IgAN in patients.

The glomerular basement membrane in lupus nephritis

Systemic lupus erythematosus is a disease that is particularly suited for studies of glomerular basement membrane pathology. Classification of the renal pathology of lupus nephritis is usually based on light microscopic features, combined with immunofluorescence findings and electron microscopic alterations. Study of renal biopsy helps to distinguish potentially reversible and irreversible disease, and to estimate prognosis of patients with lupus nephritis. Moreover, studies of human disease, as well as the availability of animal models and in vitro cell culture systems employing biochemical and molecular biological studies of extracellular matrix, have led to a considerable increase in knowledge of the pathogenetic events underlying derangements of the glomerular basement membrane in lupus nephritis.