Mesangial cell autoantigens in immunoglobulin A nephropathy and Henoch-Schönlein purpura

The Presence of ANCA in IgA Crescentic Nephropathy Does Not Lead to Worse Prognosis with Intensive Rescue Treatment

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis worldwide. The concomitant presence of both crescentic proliferation and anti-neutrophil cytoplasmic autoantibodies (ANCA) in this pathology represents a rare coincidence. However, it is not clear to what extent the presence of ANCA (IgA or IgG) in these patients could have any clinical significance. The aim of the current work is to describe the presence of ANCA (IgA or IgG) in patients with IgAN and crescentic proliferation and its possible clinical implications.

METHODS

We retrospectively recruited all patients in our center with a histological diagnosis of IgAN with crescentic proliferation between January 2013 and December 2020. The main demographic and clinicopathologic data, fundamental histological characteristics, as well as the treatments implemented and main kidney outcomes, were collected and analyzed at a 6 and 12-month follow-up.

RESULTS

Between January 2013 and December 2020, a total of 17 adults were diagnosed with concomitant crescentic proliferation through a kidney biopsy of IgAN. Five (29.4%) patients showed ANCA, three (60%) showed IgA-ANCA and two (40%) showed IgG-ANCA. All ANCA-positive patients had some degree of crescentic proliferation. At diagnosis, the mean age of patients was 48 years old (range: 27-75). Nine of them were women (52%) and the most common clinical presentation was hypertension (71%). At the time of biopsy, the mean serum creatinine and proteinuria were 2.2 mg/dL (DS 1.42) and 3.5 g/mgCr (DS 1.22), respectively, with no statistical differences between ANCA-positive and -negative patients. Histological analyses showed that 11 out of the 12 (91%) ANCA-negative IgAN patients displayed less than 25% cellular crescents, whereas 100% of ANCA-positive IgAN patients displayed more than 25% cellular crescents (p = 0.04). Notably, five (30%) patients displayed fibrinoid necrosis, with four of them (80%) being IgAN-ANCA-positive (p = 0.01). Only one ANCA-negative patient needed renal replacement therapy (RRT) upon admission (5%). The mean serum creatinine and proteinuria were 1.94 mg/dL (DS 1.71) and 1.45 g/gCr (DS 1.78), respectively, within 6 months of immunosuppressive therapy. At 12-month follow-up, the mean creatinine was 1.57 mg/dL (DS 1). Four (23.5%) patients needed RRT at the end of the follow-up and four (23.5%) patients died.

CONCLUSIONS

Probably due to the limited number of IgAN-ANCA-positive and IgAN-ANCA-negative patients, no significant differences were found between the clinical and laboratory characteristics. IgAN-ANCA-negative patients seemed to display less extracapillary proliferation than IgAN-ANCA-positive patients, who tended to show significantly higher fibrinoid necrosis. There were no differences regarding renal prognosis and patient survival after aggressive immunosuppressive therapy within 6 and 12 months when comparing the two samples.

Why, when and how should immunosuppressive therapy considered in patients with immunoglobulin A nephropathy?

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Lifelong mesangial deposition of IgA1 complexes subsist inflammation and nephron loss, but the complex pathogenesis in detail remains unclear. In regard to the heterogeneous course, classical immunosuppressive and specific therapeutic regimens adapted to the loss of renal function will here be discussed in addition to the essential common renal supportive therapy. Renal supportive therapy alleviates secondary, surrogate effects or sequelae on renal function and proteinuria of high intraglomerular pressure and subsequent nephrosclerosis by inhibition of the renin angiotensin system (RAASB). In patients with physiological (ΔGFR < 1·5 ml/min/year) or mild (ΔGFR 1·5-5 ml/min/year) decrease of renal function and proteinuric forms (> 1 g/day after RAASB), corticosteroids have shown a reduction of proteinuria and might protect further loss of renal function. In patients with progressive loss of renal function (ΔGFR > 3 ml/min within 3 months) or a rapidly progressive course with or without crescents in renal biopsy, cyclophosphamide with high-dose corticosteroids as induction therapy and azathioprine maintenance has proved effective in one randomized controlled study of a homogeneous cohort in loss of renal function (ΔGFR). Mycophenolic acid provided further maintenance in non-randomized trials. Differentiated, precise, larger, randomized, placebo-controlled studies focused on the loss of renal function in the heterogeneous forms of IgAN are still lacking. Prospectively, fewer toxic agents will be necessary in the treatment of IgAN.

IgA Structure Variations Associate with Immune Stimulations and IgA Mesangial Deposition

IgA1 mesangial deposition is the hallmark of IgA nephropathy and Henoch-Schönlein purpura, the onset of which often follows infections. Deposited IgA has been reported as polymeric, J chain associated, and often, hypogalactosylated but with no information concerning the influence of the IgA repertoire or the link between immune stimuli and IgA structure. We explored these issues in the α1KI mouse model, which produces polyclonal human IgA1 prone to mesangial deposition. Compared with mice challenged by a conventional environment, mice in a specific pathogen-free environment had less IgA deposition. However, serum IgA of specific pathogen-free mice showed more galactosylation and much lower polymerization. Notably, wild-type, α1KI, and even J chain-deficient mice showed increased polymeric serum IgA on exposure to pathogens. Strict germfree conditions delayed but did not completely prevent deposition; mice housed in these conditions had very low serum IgA levels and produced essentially monomeric IgA. Finally, comparing monoclonal IgA1 that had different variable regions and mesangial deposition patterns indicated that, independently of glycosylation and polymerization, deposition might also depend on IgA carrying specific variable domains. Together with IgA quantities and constant region post-translational modifications, repertoire changes during immune responses might, thus, modulate IgA propensity to deposition. These IgA features are not associated with circulating immune complexes and C3 deposition and are more pertinent to an initial IgA deposition step preceding overt clinical symptoms in patients.

Differences in clinical manifestations and outcomes between adult and child patients with Henoch-Schönlein purpura

We aimed to investigate differences in clinical manifestations and outcomes between adult and child patients with Henoch-Schönlein purpura (HSP), and to analyze the factors associated with poor prognosis for HSP nephritis. This retrospective 10-yr study enrolled 160 patients with HSP who visited Severance Hospital. Purpura was mostly detected in lower extremities, but purpura in upper extremities was more frequently observed in adults than children (41.7% vs 19.3%). Children had a greater frequency of arthralgia (55.4% vs 27.1%), while adults had a greater frequency of diarrhea (20% vs 1.6%). Anemia, elevated C-reactive protein, and level of IgA were more frequently observed in adults (25% vs 7.1%, 65.6% vs 38.4%, 26.3% vs 3.5%). Renal involvement in adults was more severe than in children (79.2% vs 30.4%). Chronic renal failure showed a significant difference in outcomes of HSP between adults (10.4%) and children (1.8%) after a follow up period of an average of 27 months. Furthermore, renal insufficiency at diagnosis was significantly related to the progression to chronic renal failure. Our results showed several differences in the clinical features of HSP between adults and children. Adults with HSP had a higher frequency of renal insufficiency and worse renal outcomes than children. Renal insufficiency at diagnosis might be of predictive value for the progression to chronic renal failure in HSP patients.

Autoantibodies Against Glomerular Mesangial Cells and Their Target Antigens in Lupus Nephritis

Mesangial proliferation and deposition of immunoglobulins and complement components within glomerular mesangium was one of the important pathological features of lupus nephritis. Autoantibodies against human mesangial cells could be detected in the sera of patients with IgA nephropathy (IgAN) and Henoch-Schöenlein nephritis. We speculated that autoantibodies against human glomerular mesangial cells might play a role in the development of lupus nephritis.

OBJECTIVE

To screen autoantibodies against human glomerular mesangial cells in sera from patients with lupus nephritis and to identify their target antigens.

METHODS

Sera were collected from 96 patients with lupus nephritis as well as 25 patients with IgAN and 20 patients with idiopathic membranous nephropathy (IMN). Cell lysates of in vitro cultured human glomerular mesangial cells were used as antigens in Western-blot analysis to detect autoantibodies against human mesangial cells in sera from patients with lupus nephritis as well as IgAN and IMN. The clinical and pathological significance of the autoantibodies were further investigated.

RESULTS

Autoantibodies against human mesangial cells could be detected in 94/96 (97.9%) of the sera from patients with lupus nephritis in Western-blot analysis. Twelve protein bands could be blotted by the sera from patients with lupus nephritis. The prevalence of autoantibodies against human mesangial cells in IgAN was 14/25 (56.0%) and only seven protein bands could be blotted. Five autoantibodies (anti-18, 24, 36, 46, and 91 kD) could be detected only in sera from patients with lupus nephritis. In patients with lupus nephritis, some autoantibodies might have some relationship with gender, hematuria, ANA, anti-dsDNA or anti-ENA antibodies.

CONCLUSIONS

There are autoantibodies directly against heterogeneous antigens of human glomerular mesangial cells in sera from patients with lupus nephritis, and some of them might be associated with different clinical manifestations.

Immune modulating therapy for IgA nephropathy: rationale and evidence

Our current understanding of the initial pathogenetic steps in IgA nephropathy (IgAN) provides relatively limited rationale for immunosuppressive therapy. However, it is conceivable that immunosuppressive drugs might affect secondary inflammatory events triggered by glomerular immune deposits or even proteinuria per se. Some, but not all, randomized clinical trials on either corticosteroid monotherapy, mycophenolate mofetil monotherapy, or immunosuppressive combination therapy have provided evidence for a benefit on either surrogate parameters such as proteinuria or hard end points such as renal failure. The central problem of these studies is that most were designed in the 1980s or 1990s, when recommendations for supportive therapy were strikingly different from those of today. In the meantime an equal number of randomized clinical studies reporting a benefit of supportive therapy has been published only regarding patients with IgAN and, unfortunately, no head-to-head comparisons of these 2 approaches currently are available. Several ongoing clinical trials may help to resolve this dilemma. Until the data of such studies become available, a pragmatic approach is to first optimize supportive therapy and reserve immunosuppressive medication for those patients failing a supportive approach and remaining at risk for progressive loss of renal function.

Mesangial autoantigens in IgA nephropathy: matrix synthesis and localization

Primary IgA nephropathy, a chronic nephritis with variable prognosis, is characterized by mesangial immunoglobulin A, frequently with codeposition of other immunoglobulin isotypes and complement components accompanying matrix expansion typically preceding glomerular scarring. Glomerular immunoglobulin G, when present, is localized to the mesangial periphery found variably in repeat biopsies. IgG anti-mesangial cell autoantibodies (IgG-MESCA) in sera of patients with IgA nephropathy, specific by F(ab')(2) binding to 48- and 55-kD autoantigen(s) could account for these deposits, but their in vivo localization, and the functional role in promoting scarring is unknown. A specific monoclonal antibody raised previously to these human mesangial cell autoantigen fractions, in this study localized to similar glomerular sites, reinforcing the view that immunoglobulin G deposition in vivo is a result of antibody-autoantigen binding. The propensity for immunoglobulin G more than other isotypes to enhance inflammation prompted study of its functional role in vitro. Using cultured human mesangial cells in a complement-free tritiated glycosaminoglycan synthesis single outcome assay, purified IgG fractions from patient sera increased matrix production in a dose-dependent manner compared with controls. At a constant total IgG concentration, matrix synthesis was proportional to the titre of IgG-MESCA. Autoreactive IgG stimulated matrix synthesis when compared with controls or IgA fractions. These findings are consistent with IgG-MESCA autoantibodies enhancing mesangial matrix synthesis in vitro, which suggests that in IgA nephropathy, similar prosclerotic autoimmune mechanisms might operate. Recombinant TGFbeta(1) also induced matrix synthesis, raising the possibility that both autoimmune mechanisms and those TGFbeta(1)-dependent are functional or inter-related. The pathogenesis of glomerular scarring and loss in IgA nephropathy may include, in part, these mechanisms.

Non-DNA-Binding Antibodies in Patients with Lupus Nephritis Could Recognize Membrane Proteins of Glomerular Mesangial Cells

Lupus nephritis (LN) is a prototypic autoimmune disease, however, the precise immuno-pathogenesis of LN remains to be elucidated. In our previous studies, autoantibodies against mesangial cells had been identified in sera from patients with lupus nephritis and could bind the membrane proteins of human mesangial cells (HMC) directly through antigen-antibody interaction without DNA bridge. The current study is to investigate whether the autoantibodies were associated with anti-DNA antibodies and their target antigens distribution in different cell types. Sera from nine patients with renal biopsy proven lupus nephritis with positive anti-dsDNA antibodies and four healthy subjects were collected. IgG was isolated by Protein G affinity chromatography and then non-DNA-binding IgG fractions were obtained after deletion of anti-DNA antibodies using a DNA-cellulose affinity column. Membrane proteins, obtained from HMC, human umbilical vein endothelial cells (HUVEC), peripheral mononuclear cells by sonication and sequential centrifugation, were solubilized and applied in Western-blot analysis to characterize the target antigens. In results, the non-DNA-binding IgG fractions from sera of patients with lupus nephritis could blot the protein(s) of HMC membrane at 74, 63, and 42 kD. However, only a similar 74-kD protein could be blotted on membrane of HUVEC, and the target antigens on membranes of mononuclear cells were heterogeneous. In conclusion, our preliminary study had demonstrated that non-DNA binding autoantibodies against mesangial cells could be found in sera from patients with lupus nephritis. Although the target antigens might not be cell specific, the roles of these autoantibodies in the pathogenesis of lupus nephritis need further investigation.

Pathogénie des vascularites systémiques primitives (II): vascularites ANCA-négatives

The pathogenesis of different types of systemic vasculitis negative for antineutrophil cytoplasm antibodies (ANCA) and involving small or medium-sized vessels is not very well documented. During polyarteritis nodosa (PAN), which is related to hepatitis B virus (HBV) infection, as well as during cryoglobulinemic vasculitides, associated with hepatitis C virus (HCV), and probably during Henoch Schönlein purpura, histological lesions may result from the deposition of immune complexes formed from viral antigens and from antibodies responsible for the activation of the classic complement pathway and for recruitment of polymorphonuclear neutrophils. Two other mechanisms are discussed for other types of ANCA-negative systemic vasculitis: immune complex deposition and sheer stress at arterial bifurcation points. A bacterial superantigen is suspected in Kawasaki disease but remains unproved.

Characterization of Anti-Mesangial Cell Antibodies and Their Target Antigens in Patients with Lupus Nephritis

The pathogenetic mechanisms of lupus nephritis (LN) remain to be elucidated. In our previous study, autoantibodies against human glomerular mesangial cells (HMC) were identified in sera of most patients with lupus nephritis. The current study is to investigate the binding characteristics of anti-mesangial cell antibodies to human mesangial cell membrane. Serum samples were collected from 54 patients with renal biopsy proven lupus nephritis, 12 patients with systemic lupus erythematosus without clinical renal involvement, and 15 healthy subjects. Membrane proteins were obtained from in vitro cultured HMC by sonication and sequential centrifugation. DNase I were employed to remove DNA fragments in sera and membrane protein preperation and IgG F(ab')2 was obtained by pepsin digestion. Western Blot analysis was used to characterize the antibody and antigen interaction. In results, 25 of 54 (46.3%) sera from patients with lupus nephritis had anti-mesangial cell antibodies targeted at 74 kDa, 63 kDa, 52 kDa and 42 kDa protein bands of HMC membrane. Only four of 12 (33.3%) sera from patients without renal involovement recognized the protein bands at 74 kDa and 63 kDa, but not 52 kDa and 42 kDa. DNase treatment of the HMC membrane and the sera did not affect the binding. IgG F(ab')2 from sera of 10 patients with positive anti-mesangial cell antibodies could still bind the 63 kDa protein. In conclusion, anti-mesangial cell antibodies from sera of patients with lupus nephritis could bind membrane proteins of HMC directly without a DNA bridge and the binding was through antigen-antibody interation. Anti-mesangial cell antibodies might play some role in the pathogenesis of lupus nephritis(LN).

Role of Bartonella henselae in the etiology of Henoch-Schönlein purpura

BACKGROUND

The etiology of Henoch-Schönlein purpura (HSP) has been ascribed to a variety of infectious and noninfectious agents. Because we encountered a patient with HSP who had evidence of Bartonella henselae infection and a prior report of a patient with systemic cat-scratch disease presenting as leukoclastic vasculitis, we investigated the association of B. henselae infection with HSP.

METHODS

We determined the antibody titers to B. henselae on the sera of 18 patients with HSP and on 57 controls. All patients presented with the characteristic leukoclastic rash of HSP. About one-half of the patients had joint or abdominal symptoms, and four had hematuria at presentation. An indirect immunofluorescent assay was used to determine serum antibody titers to B. henselae. Sera that were reactive at a dilution of 1/64 were considered positive.

RESULTS

Eight of the 57 (14%) control sera and 12 of the 18 (67%) patient sera were positive for B. henselae antibody (P < 0.0001).

CONCLUSION

The results of this study indicate a significant association of antecedent B. henselae infection with HSP. The frequency of this association (67%) exceeds that of previously ascribed etiologic agents for this disease, such as the group A Streptococcus.

Effects of all-trans retinoic acid on renin-angiotensin system in rats with experimental nephritis

We previously demonstrated that all-trans retinoic acid (RA) preserves glomerular structure and function in anti-Thy1.1 nephritis (Wagner J, Dechow C, Morath C, Lehrke I, Amann K, Floege J, and Ritz E. J Am Soc Nephrol 11: 1479-1489, 2000). Because the renin-angiotensin system (RAS) contributes to renal damage, we 1) studied retinoid-specific effects on its components and 2) compared the effects of all-trans-RA with those of the AT(1)-receptor blocker candesartan. Rats were pretreated for 3 days before injection of the OX-7 antibody and continued with treatment with either vehicle or daily injections of 10 mg/kg all-trans-RA only (study 1) or 10 mg/kg body wt all-trans-RA, 1 mg/kg candesartan, or both (study 2) for an additional 7 days. The blood pressure increase observed in anti-Thy1.1 nephritic rats was equally normalized by all-trans-RA and candesartan (P < 0.05). In nephritic rats, mRNAs of angiotensinogen and angiotensin-converting enzyme (ACE) in the kidney were unchanged, but renin mRNA was lower (P < 0.01). Renal and glomerular AT(1)-receptor gene and protein expression levels were higher in anti-Thy1.1 nephritic rats (P < 0.05). In the renal cortex of nephritic rats, pretreatment with all-trans-RA significantly reduced mRNAs of all the examined RAS components, but in the glomeruli it increased ACE gene and protein expression (P < 0.01). In nephritic rats, candesartan reduced the number of glomerular cells and mitoses (P < 0.05) less efficiently than all-trans-RA (P < 0.01). Both substances reduced cellular proliferation (proliferating cell nuclear antigen) significantly (P < 0.05). No additive effects were noted when both compounds were combined. In conclusion, all-trans-RA influences the renal RAS in anti-Thy1.1 nephritis by decreasing ANG II synthesis and receptor expression. The beneficial effect of retinoids may be explained, at least in part, by reduction of RAS activity.

Schönlein-henoch purpura in children and adults: diagnosis, pathophysiology and management

Schönlein-Henoch syndrome is a form of systemic small-vessel vasculitis, characterised by vascular and/or mesangial immunoglobulin A1 deposits. The main clinical manifestations are vascular purpura, predominating on the lower limbs, and articular, gastrointestinal and renal symptoms. Pulmonary, cardiac, genital and neurological symptoms have also be observed. The syndrome usually affects children, whereas it is rare in adults. The frequency of renal involvement varies between individual studies (from 20 to 100%). Renal manifestations are usually mild and transient, although chronic nephropathies may occur. Overall, an estimated 2% of children with Schönlein-Henoch purpura progress to renal failure and up to 20% of children with nephritis treated in specialised centres require haemodialysis. The renal prognosis appears to be worse in adults. Aetiological investigations are required, as a triggering factor is found in approximately half the patients (e.g. viral, bacterial and parasitic infections, drugs, toxins, systemic diseases and cancer). Dapsone has beneficial effects on cutaneous, gastrointestinal and articular manifestations in adults, especially those with chronic forms. Corticosteroids may be useful for refractory abdominal pain. Methylprednisolone pulse therapy, immunosuppressive drugs (e.g. cyclophosphamide and azathioprine), plasma exchange and polyclonal immunoglobulin therapy are beneficial in very rare life-threatening forms of the disease and in rare instances where renal function is compromised.

Alteration of lung diffusion capacity in IgA nephropathy

OBJECTIVE

To establish whether changes of lung transfer for carbon monoxide (TLCO) are related to the phase of IgA nephropathy.

METHODS

Respiratory function was tested in 12 children with IgA nephropathy assessed by percutaneous renal biopsy. This was done during acute exacerbations or haematuria-free phases of the disease.

RESULTS

TLCO was low in 12/13 measurements made in the haematuric phase of IgA nephropathy or during the month following gross haematuria (mean TLCO 64% of expected values). Lung volumes and blood gas values were normal and only minor radiological signs of interstial lung involvement were observed in 11/12 patients. When respiratory tests were performed more than three months after gross haematuria, TLCO was low in 4/9 patients, with no relation to the significance of residual proteinuria or severity of findings at renal biopsy. There was a significant difference between tests performed when haematuria was present or recent and those performed more than three months after an episode of gross haematuria (p < 0.01).

CONCLUSIONS

The decrease of TLCO in the acute phases of the disease is probably related to alterations of the lung alveolarcapillary membrane by immune complexes containing IgA. This non-invasive technique, easy to perform and repeat, could be of value in the diagnosis of IgA nephropathy in haematuric children.

Chronic glomerulonephritis in childhood. Membranoproliferative glomerulonephritis, Henoch-Schönlein purpura nephritis, and IgA nephropathy

The chronic glomerulonephritides that lead to permanent loss of renal function may present with an acute nephritic syndrome, nephrotic syndrome, or asymptomatic hematuria and proteinuria. Membranoproliferative glomerulonephritis, Henoch-Schönlein purpura nephritis, and IgA nephropathy are common childhood glomerulonephritides that may lead to chronic renal failure. Their clinical manifestations, natural history, and long-term prognosis are distinct. This article reviews various presentations of these common childhood glomerulonephritides and an approach to management and potential therapy.

IgA nephropathy

IgAN is the most common type of glomerulonephritis worldwide, and is found more in men and distinctly less in blacks. It presents with macroscopic hematuria in about 40 to 45% of patients, with microscopic hematuria and proteinuria in about 35 to 40%, and with nephrotic syndrome or acute renal failure in the remainder. The diagnosis continues to rely on the finding of the dominant or codominant mesangial deposition of IgA on immunohistologic examination of the kidney. No blood or urine test is sufficiently reliable for diagnosis. While the pathogenesis remains unknown, accumulating evidence suggests that polyclonal stimulation of immunoglobulins perhaps coupled with structural abnormalities of IgA play pivotal roles. These defects may account for the variety of autoantibodies detected in patients with both IgAN and HSP. While IgAN has an indolent course, about 30% of patients will reach ESRD after 20 years, particularly in those who present with hypertension, heavy proteinuria or renal insufficiency. At present, therapy is disappointing, but immunoglobulin supplementation and newer agents that interrupt the pathways of mesangial proliferation and sclerosis hold promise for the future. Kidney transplantation has shown excellent allograft survival.

Binding of dimeric and polymeric IgA to rat renal mesangial cells enhances the release of interleukin 6

The mesangium plays a crucial role in processes of inflammation in the kidney. Since deposits of IgA in the mesangium in patients with IgA nephropathy suggest a role for IgA in the inflammatory process, we investigated whether IgA is able to bind to cultured rat mesangial cells (MC) in vitro and induce activation of MC. As a source of IgA, monomeric (mIgA), dimeric (dIgA) and polymeric IgA-alpha-DNP (pIgA) rat monoclonal antibodies were used. FACS analysis indicated binding of dIgA and pIgA to MC while only a small percentage of the cells exhibited binding of mIgA. Additional experiments employing radiolabeled IgA revealed a time- and dose-dependent binding of 125I-dIgA and 125I-pIgA with 6 x 10(6) binding sites for dIgA with an affinity of 5.5 x 10(6) M-1 and 7.2 X 10(6) binding sites/cell for pIgA with an affinity of 1.2 x 10(6) M-1. As compared to 125I-dIgA and 125I-pIgA, little binding of 125I-mIgA to MC occurred; the binding of dIgA and pIgA was not influenced by excess cold BSA, IgG or asialofetuin. Since some studies have suggested that fibronectin might interact with IgA, the binding of IgA to MC in the presence or absence of fibronectin or the RGD fragment was also analyzed. However no influence of fibronectin or the RGD fragment on binding of dIgA and pIgA to MC was observed. As a measure for activation of MC by IgA, the production of IL-6 by MC was analyzed. Dimeric IgA and pIgA both induced a dose-dependent increase of IL-6 production by MC.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoantibodies from mixed cryoglobulinaemia patients bind glomerular antigens

Mixed cryoglobulinaemia (MC) is a disorder characterized by the presence of large amounts of cryoprecipitating IgM-IgG complexes. An immune complex glomerulonephritis develops in one third of all patients, but its occurrence does not seem related to the amount of cryoglobulins in the sera, nor to their complement-fixing ability. In this study we investigated the presence of IgG antibodies reactive with kidney antigens in 33 MC patients (11 with glomerulonephritis, 22 without renal involvement). A total glomerular extract was run on a 10% acrylamide gel, blotted to nitrocellulose and probed with the patients' sera. Sera from half of the patients without renal involvement reacted with several glomerular antigens whose molecular weight ranged between 200 and 29 kD. In the group with renal involvement, sera from 7/11 patients reacted with an antigen of 50 kD, which is also expressed in thymus, but not in the heart or liver. In a follow-up study of four patients with renal involvement, the amount of serum antibody specific for the 50-kD antigen fluctuated, either spontaneously or in response to therapy. These results show that antibodies specific for glomerular antigens are detectable in MC sera. The immune response against a 50-kD antigen expressed in the kidney and thymus seems to be restricted to a subset of MC patients with renal involvement. Circulating autoantibodies specific for glomerular antigens might contribute to the induction of glomerulonephritis in MC forming immune complexes in situ.

Activation of autoreactive T-lymphocytes by cultured syngeneic glomerular mesangial cells

The capacity of intrinsic, glomerular mesangial cells (MC) to cause an autoreactive response of syngeneic lymphocytes in vitro are presented. Initial experiments demonstrated the MHC class II dependent capacity of MC to present exogenous antigen to sensitized lymph node lymphocytes (LN) and to activate naive, allogeneic LN in the absence of a nominal antigen. However, the most striking finding of the present investigation was that mouse MC (C57BL/6 or DBA/2) augmented a significant activation of naive, syngeneic lymphocytes. The extent of the proliferative lymphocyte response was comparable to that observed after stimulation with allogeneic MC. Moreover, during syngeneic coculture substantial amounts of interferon bioactivity were generated. Equipotent concentrations of rm IFN-gamma were sufficient to induce class II MHC expression of mouse MC. In control experiments the macrophage cell line, IC-21 (C57BL/6), or freshly prepared DBA/2 mouse peritoneal macrophages did not elicit a syngeneic LN response. Using MC, which had not been pretreated, the MC-specific LN stimulation occurred after prolonged periods of coculture. The stimulation index (S.I.) was 9.77 after 144 hours compared with LN controls (S.I. = 1). However, a 48 hour pretreatment of MC with either rm IFN-gamma alone or in combination with rh TNF-alpha and/or the continuous presence of rm IL-1 alpha during coculture periods from 72 to 144 hours substantially enhanced the proliferative LN response. Analysis of non-adherent LN by flow cytometry (FACS) after 96 or 120 hours coculture with MC revealed an increased ratio of Thy1.2+ to B220+ cells with a predominant rise of L3T4+ T-helper cells compared to Lyt2+ cytotoxic T-cells. Furthermore, immune fluorescence microscopy showed that a fraction of Thy1.2+ lymphoblasts adhered to MC. FACS analysis of these adherent LN after detachment demonstrated that in comparison to cocultures with untreated MC, cocultures of LN with IFN-gamma/TNF-alpha pre-treated MC resulted in a 24.4% increase of Thy1.2+ cells, with 89% of these being L3T4+ T-helper lymphocytes. In conclusion, autoreactivity of preferentially T-helper cells to cocultured glomerular MC was shown, which may represent a useful model of T-lymphocyte dependent glomerulonephritis.

Etiology of IgA nephropathy syndrome

Since Berger's original paper on mesangial IgA-IgG deposition with hematuria, there have been a number of clinical and pathological studies regarding IgA immune complexes, the mechanisms of glomerular IgA deposition leading to glomerular injury and animal models of IgA nephropathy. During the last quarter of this century, glomerular changes such as IgA nephropathy have also been observed in cases associated with other diseases, such as systemic lupus erythematosus, Schoenlein-Henoch purpura, liver cirrhosis and chronic inflammatory diseases of the lung. This evidence supports the idea of an IgA nephropathy syndrome. On the other hand, IgA is thought to be an important humoral factor at the mucosal immune system and appears to have an antibody function against various etiologic candidates of extrinsic or intrinsic substances at the mucosal and systemic immune system. Glomerular IgA deposition in IgA nephropathy syndrome is thought to result from elevated levels of circulating immune complexes or aggregated IgA due to an overproduction of polymeric IgA as antibodies in the serum and due to the clearance impairment of IgA immune complexes in the hepatic and splenic phagocytic system. The glomerular IgA subclass is not one-sided, but should be evaluated in comparison with the age of patients at renal biopsy; this indicates the approximate age of onset. Cirrhotic IgA glomerulonephritis is not related to Hepatitis B or C virus infection, but to the pathophysiologic condition of liver cirrhosis. Various etiologic candidates such as viral, microbial, dietary antigens or auto-antigens have been listed and experimental models of IgA nephropathy syndrome have provided some clues in understanding the etiology of primary IgA nephropathy. However much still remains to be clarified and some specific epitopes common among these etiologic candidates will have to be identified.

Low antibody affinity restricted to the IgA isotype in IgA nephropathy

Antibody affinity affects the handling and behaviour of immune complexes, and experimental studies have shown that animals which produce predominantly low-affinity antibody are prone to immune complex deposition resulting in glomerulonephritis. In order to investigate the potential role of antibody affinity in the pathogenesis of IgA nephropathy, affinity of both IgA and IgG antibody isotypes during secondary response to systemic immunization with tetanus toxoid was studied in 20 patients with IgA nephropathy. Patients with IgA nephropathy produced IgA antibodies of significantly lower affinity than controls (P < 0.001), whereas IgG antibody affinities were similar. Contrasting with controls, patients' IgA antibody affinity was inversely related to antibody concentration, with higher responders producing large amounts of low-affinity antibody. IgG antibody affinity increased with time, and maturation of IgG antibody affinity was similar in both controls and patients. IgA affinity in controls decreased with time, and this lack of IgA affinity maturation may explain the relative unimportance of IgA in normal systemic immunity. This temporal decrease in IgA affinity was not observed in patients with IgA nephropathy. The production of low-affinity IgA in IgA nephropathy may provide an explanation for the predominant deposition of IgA in this disease.

Detection of abnormal peripheral blood mononuclear cell cytokine networks in human IgA nephropathy

Dysregulated cytokine expression has been implicated in the pathogenesis of IgA nephropathy, but the mechanisms and selectivity of this response are poorly understood. In this study we have examined the expression of a range of immunoregulatory cytokine mRNAs by peripheral blood mononuclear cells (PBMNCs) from 45 patients with IgA nephropathy stratified empirically according to urinary red cell excretion: 10 in remission, and 35 with active disease (21 mild, 14 moderate), and 17 normal, and 15 disease, controls. We used a semi-quantitative polymerase chain reaction (PCR) technique. None of the patients had experienced recent episodes of macroscopic hematuria. Simultaneous analysis of monocyte class II antigen (DR) expression was also performed by two-color immunoflow cytometry. TGF-beta 1 mRNA was detected in 68% (24 of 35) of patients with active, and 70% (7 of 10) inactive IgA nephropathy, but in only 18% (3 of 17) normal (P < 0.005), and 27% (4 of 15) disease controls. IL-6 transcripts were identified in 37% (13 of 35) of patients with active IgA nephropathy, compared with 6% (1 of 17) normal controls (P = 0.015), with no significant increase in IgA remission, or disease control groups. TNF-alpha mRNA was detected in 29% (5 of 17) of normal and 53% (8 of 15) disease controls, but in only 7% (3 of 35) of patients with IgA nephropathy (P = 0.015). There was no significant change in TGF-beta 2, gamma-IFN, IL-2, IL-4, IL-1 alpha or IL-1 beta detection between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat glomerular mesangial cells synthesize basic fibroblast growth factor. Release, upregulated synthesis, and mitogenicity in mesangial proliferative glomerulonephritis

Mesangial injury and cell proliferation are frequent findings in various glomerular diseases in man. Previous studies have demonstrated that basic fibroblast growth factor (bFGF) is a potent mesangial cell mitogen in vitro. To further elucidate the role of bFGF in rat mesangial cell (RMC) proliferation, we examined whether RMC synthesize bFGF in vitro and whether bFGF is involved in mesangial proliferation in vivo. Cultured RMC expressed bFGF protein (23, 21.5, and 18 kD forms) and bFGF mRNA, and released biologically active bFGF into the culture medium after antibody- and complement-mediated injury. Normal rat glomeruli in vivo contained no detectable bFGF mRNA, but bFGF protein (23 and 21.5 kD) could be demonstrated, which immunolocalized to the mesangium. Glomerular bFGF decreased markedly during the acute phase of glomerulonephritis induced by anti-Thy 1.1 antibody, compatible with mesangial bFGF release after complement-mediated mesangiolysis. During the subsequent mesangial proliferative phase, glomerular bFGF protein and mRNA increased above normal. Intrarenal infusion of heparin did not affect the bFGF immunostaining of glomeruli at this stage, indicating a predominantly intracellular localization of the bFGF. The capability of bFGF to mediate proliferation in the anti-Thy 1.1 model was further supported by experiments in which intravenous bFGF given 24 h after a subnephritogenic dose of anti-Thy 1.1 antibody led to a 4.9- to 5.1-fold increase in glomerular cell proliferation (with > 60% of the cells identified as mesangial cells by double immunolabeling). No such increase was observed in normal rats injected with bFGF. These data show that mesangial cells produce and release bFGF after injury and that bFGF is mitogenic for injured mesangial cells in vivo. Release of mesangial cell bFGF thus may be an important mechanism involved in the initiation of mesangial cell proliferation in vivo.

Mesangial cells in the pathogenesis of progressive glomerular disease in animal models

Increasing evidence supports a role for glomerular mesangial cell proliferation and over-production of extracellular matrix by mesangial cells in the development of focal or diffuse glomerulosclerosis. Experimental data obtained mainly in the chronic progressive remnant kidney model and in the acute mesangioproliferative anti-Thy 1.1 glomerulonephritis in rats have shed some insights into the factors governing mesangial cell proliferation and matrix synthesis in vivo. In these experimental models, mesangial cell activation can be demonstrated early in the course of disease as exemplified by the de novo expression by the mesangial cell of a smooth muscle "specific" actin isotype (i.e., alpha-smooth muscle actin). Following mesangial cell activation, cellular proliferation ensues both in the acute anti-Thy 1.1 model and, to a lesser degree, in the chronic remnant kidney model. While a multitude of mitogens for mesangial cells has been proposed on the basis of in vitro experiments, the factors involved in the regulation of mesangial cell proliferation in vivo remain largely undefined. Three growth factors which may have important roles in the in vivo mesangioproliferative response are platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and transforming growth factor-beta (TGF-beta). All three cytokine growth factors are present in various inflammatory cells as well as in mesangial cells themselves, thereby allowing these factors to mediate cell proliferation by either paracrine and/or autocrine pathways. In vivo studies show that PDGF, bFGF, and TGF-beta participate in the mesangial cell proliferation and/or the mesangial matrix expansion that follows mesangial cell injury with anti-Thy 1.1 antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta in disease: the dark side of tissue repair

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