Heymann nephritis: mechanisms of renal injury

Ultrastructural change of the glomerular basement membrane in rats with Heymann nephritis revealed by ultrahigh resolution scanning electron microscopy

To assess the relationship between the glomerular injury induced by immune complex deposition and proteinuria, ultrastructural changes of the glomerular basement membrane (GBM) were investigated in Heymann nephritis. Active Heymann nephritis was induced in rats by injecting them with tubular brush border antigen, known as Fx1A, emulsified in complete Freund's adjuvant (CFA). Measurement of urinary protein excretion and histological examinations were carried out for up to 15 weeks after immunization. Proteinuria developed in rats within 10 weeks of immunization and coincided with the development of subepithelial deposits with minimal spike-like basement membrane protrusion. Acellular glomeruli were prepared by detergent treatment and were subjected to tannic acid-osmium conductive staining prior to examination with an ultrahigh resolution scanning electron microscope (HSEM). HSEM of the acellular GBM prepared from control rats injected with CFA alone revealed a meshwork structure, with pores of about 9 nm in diameter. Proteinuric rats immunized with Fx1A showed a loosened meshwork structure, with pores of about 15 nm in the acellular GBM adjacent to the deposits. The newly formed GBM overlying the deposit consisted of a meshwork structure associated with unorganized thin fibrils. Ultrastructural changes were never seen in GBM devoid of deposits. These findings indicate that subepithelial deposits are closely involved in the development of proteinuria by injuring the size selectivity of the GBM.

Active Heymann nephritis in complement component C6 deficient rats

The mechanisms of renal injury that result in proteinuria in active Heymann nephritis (AHN) remain unclear, though data suggest that in analogy of the passive form of the disease the membrane attack complex C5b-9 may be involved. AHN was induced in an inbred strain of PVG/c-rats that are totally deficient in the C6 component of complement and are unable to form the lytic C5b-9 complex, as well as in non-complement deficient PVG/c+ rats that are immunologic identical to the deficient strain. In both groups of animals comparably high titers of anti-Fx1A autoantibodies were found after three weeks and persisted at 40 weeks. Proteinuria was also similar in both groups, and was first evident at six weeks. High levels of urinary protein, ranging from 200 mg/24 hr to 500 mg/24 hr, were found after 10 weeks and persisted up to one year. Renal biopsy findings at various times post-immunization were identical in both groups, including immunofluorescence staining for Ig and C3 deposits, and also EM findings of subepithelial electron-dense deposits were not different. The injection of heterologous rabbit complement, that partially and temporarily restored the CH50 activity in PVG/c- rats did not alter or hasten the disease. Long-term follow-up showed that all rats in both groups continued to have severe proteinuria and that most animals died between 8 to 12 months after disease induction, without renal impairment. EM findings in serial biopsies demonstrated that the growth of the subepithelial deposits as measured by surface area occurred between weeks 4 and 12. A positive correlation (r = 0.94) between the size of the deposits and the level of proteinuria was found. These studies demonstrate that the membrane attack complex of complement does not play a major role in AHN. The relationship of the size of the immune deposits to the level of proteinuria suggests that the growth of the immune deposits on itself initiate secondary mechanisms that damage the permselective characteristics of the glomerular membrane.

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.

gp330 and RAP: the Heymann nephritis antigenic complex

It is apparent that significant progress has been made in the characterization of gp330 in the years that have elapsed since its initial identification as the nephritogenic antigen of Heymann nephritis. However, there are still many gaps in our knowledge and we do not yet have a full picture of the molecular events leading to the formation of immune deposits in glomerular capillaries. Moreover, we still do not have direct information on the normal function(s) of gp330 and RAP and their trafficking in renal and other epithelia. The availability of the yolk sac and other cell lines that express gp330 and RAP together with the identification of the functional domains of RAP should greatly facilitate experimental studies designed to elucidate these problems. Progress will also be greatly facilitated in the future when the complete amino-acid sequence of gp330 becomes available, making possible further structural studies. It is our hope that new knowledge obtained on the molecular mechanisms of HN will provide insights into the molecular pathogenesis of human membranous nephropathy and will provide a strategy for the design of appropriate treatments to interrupt the process.

Hereditary C6 deficiency in a strain of PVG/c rats

A chance observation has led to the discovery of a strain of PVG rats (PVG/c-) which are deficient in complement (C) component C6. Analysis of total haemolytic activity (CH50) of PVG/c- serum revealed an absent CH50 activity compared with serum of other rat strains and of a PVG/c rat (PVG/c+) that showed normal C activity. Thus, the PVG/c- rat was unable to activate the C5b-9 membrane attack complex. To gain insight into the complement abnormalities, analysis of individual C components was performed. Testing the PVG/c- serum in a C6 haemolytic assay and using deficient human sera showed a deficiency of C6 in the PVG/c- rat. Highly purified human C6 and human sera deficient in other components were able to reconstitute the CH50 activity of the PVG/c- rat. The possibility that an inactivator of C was present in PVG/c- serum was excluded. The deficiency was found to be inheritable and under the control of an autosomal recessive gene. Furthermore, tissue antigens and immunity of the PVG/c- rat were found to be identical to those determined in the PVG/c+ rat. With regard to their health status, the PVG/c- animals seem to have no disadvantages compared with PVG/c+ rats when held under the same conditions within the protected environment of animal facilities. Taken together, both rat strains provide an unique animal model for studying the biological role of C, particularly the C5b-9 membrane attack complex in experimental medicine.

Partial prevention of active Heymann nephritis by 1 alpha, 25 dihydroxyvitamin D3

The hormone 1 alpha, 25 dihydroxyvitamin D3 (1,25(OH)2D3) has potent immunosuppressive effects in vitro. Recent publications also described a protective effect of the hormone in various animal models of immune-mediated diseases. To test its in vivo activity we induced active Heymann nephritis in Lewis rats that were either untreated or treated with 1,25(OH)2D3 or its synthetic 20-epi analogue, KH1060. Treatment with cyclosporine A (CsA) was used as an immunosuppressive control. In this nephrotic model the administration of 1,25(OH)2D3 (0.5 microgram/kg body weight) given on alternate days during the first 13 days after active immunization significantly reduced the proteinuria as measured by weeks 7-9. This reduction was comparable to the reduction observed in rats treated with CsA (20 mg/kg) on alternate days. A second series of experiments with 1,25(OH)2D3 confirmed these findings. The level of autoantibodies was found to be significantly suppressed during the treatment time in the CsA (20 mg/kg) group, whereas the limit of significance (P = 0.06) was reached in the 1,25(OH)2D3 (0.5 microgram/kg) group. The size of the immune deposits also was found to be substantially smaller in the groups that developed less proteinuria. The administration of 1,25(OH)2D3 transiently increased the mean serum calcium concentration with 2.5 mg/dl above the pretreatment values, and the urinary calcium excretion by a factor of 3-5 during the short treatment time. Treatment with the analogue KH1060 did not reduce the proteinuria significantly. Our experiments add evidence to the hypothesis that 1,25(OH)2D3 in pharmacological doses has immunosuppressive potency.

Current topics in childhood lupus nephritis

Lupus nephritis is a major predictor of the prognosis of systemic lupus erythematosus (SLE). The present paper discusses lupus nephritis from clinical and immunopathological points of view. Although recent advances in diagnosis and treatment improve the prognosis of children with SLE, there remain many unsolved clinical problems. One of the current topics in the treatment for SLE is intermittent intravenous cyclophosphamide therapy which is effective even for the steroid-resistant patients with severe lupus nephritis, at least for short-term observation. Immunopathologically, the following issues are discussed: (i) The C5b-9 terminal complement complex plays an important role in the pathogenesis of lupus nephritis. The possible interaction of vitronectin and SP-40,40 is also mentioned; (ii) A semi-quantitative analysis of the charge barrier of the glomerular basement membrane reveals that the charge barrier dysfunction plays an important role in the pathogenesis of proteinuria in lupus nephritis. This study also demonstrates that the charge of immune deposits is important for the initiation of glomerular injury in lupus nephritis; (iii) It is demonstrated that the histopathological diversity of lupus nephritis is based on biological properties of nephritogenic auto-antibodies in murine lupus models.

Leukotriene D4 is a mediator of proteinuria and glomerular hemodynamic abnormalities in passive Heymann nephritis

We assessed the role of leukotrienes (LTs) in Munich-Wistar rats with passive Heymann nephritis (PHN), an animal model of human membranous nephropathy. 10 d after injection of anti-Fx1A antibody, urinary protein excretion rate (Upr) in PHN was significantly higher than that of control. Micropuncture studies demonstrated reduced single nephron plasma flow and glomerular filtration rates, increased transcapillary hydraulic pressure difference, pre- and postglomerular resistances, and decreased ultrafiltration coefficient in PHN rats. Glomerular LTB4 generation from PHN rats was increased. Administration of the 5-LO activating protein inhibitor MK886 for 10 d markedly blunted proteinuria and normalized glomerular hemodynamic abnormalities in PHN rats. An LTD4 receptor antagonist SK&F 104353 led to an immediate reduction in Upr and to reversal of glomerular hemodynamic impairment. Ia(+) cells/glomerulus were increased in PHN rats. In x-irradiated PHN rats, which developed glomerular macrophage depletion, augmented glomerular LT synthesis was abolished. Thus, in the autologous phase of PHN, LTD4 mediates glomerular hemodynamic abnormalities and a hemodynamic component of the accompanying proteinuria. The synthesis of LTD4 likely occurs directly from macrophages or from macrophage-derived LTA4, through LTC4 synthase in glomerular cells.

Fish oil has protective and therapeutic effects on proteinuria in passive Heymann nephritis

Passive Heymann nephritis (PHN) is a rat model of membranous nephropathy induced by injecting anti-Fx1A. The onset of proteinuria in PHN is caused by complement-mediated injury to glomerular epithelial cells (GEC) accompanied by enhanced glomerular eicosanoid production. In addition, sublethal injury by complement of rat GECs in culture leads to phospholipase activation, phospholipid hydrolysis and release of arachidonic acid and dienoic prostanoids. Based on these findings, we undertook to determine if substituting arachidonic acid (omega-6) in GEC membrane phospholipids with omega-3 fatty acids derived from fish oil would alter the development and course of proteinuria in PHN. We found that rats fed a diet containing 10% fish oil for four weeks prior to antibody injection developed 50 to 60% less proteinuria between two and six weeks after anti-Fx1A than rats fed an equivalent diet containing 10% safflower oil, and had substantial enrichment of glomerular phospholipids with omega-3 fatty acids and displacement of arachidonic acid. This outcome was associated with a 50% reduction in release of glomerular thromboxane B2 (stable metabolite of thromboxane A2) in the fish oil group. More importantly, when PHN rats with well established proteinuria while on regular chow were randomized to three dietary groups, those fed fish oil had a 25 to 50% decline in proteinuria as compared to those fed lard or safflower oil. This difference was evident within two weeks of randomization and persisted until the end of the study after eight weeks. In neither study could the differences in urine protein excretion be accounted for by protein or calorie deprivation, or by differences in blood pressure, renal function, immune response to sheep IgG, or glomerular deposition of IgG or complement. Thus, our results indicate that dietary fish oil has protective and therapeutic effects with regard to proteinuria in PHN. These benefits may relate to alterations in membrane phospholipid composition in favor of omega-3 fatty acids and release of less reactive trienoic eicosanoids.

Expression of type I collagen mRNA in glomeruli of rats with passive Heymann nephritis

In passive Heymann nephritis (PHN) glomeruli exhibit marked basement membrane expansion around subepithelial immune deposits but they fail to show any change in mRNA levels of type IV collagen, laminin or fibronectin by Northern and slot-blot analysis, or in the amount or distribution of type IV collagen or laminin by immunohistology for up to 12 weeks after disease onset. On the other hand, in situ hybridization (ISH) revealed the appearance of positive cells exhibiting mRNA for the alpha 1 chain of rat type I collagen two to three weeks after the onset of PHN in all glomeruli of all rats. Positive cells persisted for at least eight weeks. In many glomeruli, the location of the clusters of silver grains suggested that they were in visceral epithelial cells. In controls injected with normal sheep IgG, and in early PHN (< 11 days after sheep anti-Fx1A), glomeruli were negative but cells in the renal capsule and adventitia of vessels showed strong ISH and served as positive controls. RNAse pre-treatment and the "sense" probe gave appropriately negative results. RNA from PHN glomeruli contained an alpha 1 type I collagen transcript of the same size as that from rat fibroblasts. These results show that the evolution of glomerular basement membrane expansion in rat membranous nephropathy coincides with the induction of a matrix gene that is not normally expressed in glomerular cells. Further, they suggest that the intercalation of ectopically-expressed matrix molecules may contribute to the production of a disorganized basement membrane.

Isolation and characterization of a membrane protein from rat erythrocytes which inhibits lysis by the membrane attack complex of rat complement

The membrane attack complex (MAC) of complement in humans is regulated by several membrane-bound proteins; however, no such proteins have so far been described in other species. Here we report the isolation and characterization of a rat erythrocyte membrane glycoprotein of molecular mass 21 kDa which inserts into cell membranes and is a potent inhibitor of the rat MAC. This protein, here called rat inhibitory protein (RIP), was first partially purified by column chromatography from a butanol extract of rat erythrocyte membranes. Monoclonal antibodies (Mabs) were raised against RIP and used for its affinity purification. Affinity-purified RIP was shown to inhibit in a dose-dependent manner the cobra venom factor (CVF)-mediated 'reactive' lysis of guinea pig erythrocytes by rat complement. Conversely, the anti-RIP MAbs 6D1 and TH9 were shown to markedly enhance the CVF-mediated lysis of rat erythrocytes by rat complement. RIP acted late in the assembly of the MAC (at or after the C5b-8 stage) and was releasable from the membranes of rat erythrocytes by phosphatidylinositol-specific phospholipase C. These features, together with its size, deglycosylation pattern and N-terminal amino acid sequence, lead us to conclude that RIP is the rat homologue of the human MAC-inhibitory protein CD59 antigen.

Renal tubular epithelial antigen-containing immune complexes stimulate interleukin-1 production by monocytes from patients with glomerulonephritis

We have investigated the effect of immune complexes (IC) derived from human renal tubular epithelial (RTE) antigen on the release of interleukin-1 (IL-1) in monocyte cultures from patients with glomerulonephritis (GN). When peripheral blood monocytes (PBM) were activated by IC, substantial amounts of IL-1 could be detected in the supernatants as measured by mouse thymocyte assay. The IC-induced IL-1 activity was significantly higher in patients with GN than in normal controls. To avoid the effect of prostaglandins on the IL-1 assay, we cultured PBM with addition of indomethacin and assayed IL-1 activity in the culture supernatants. This cyclooxygenase inhibitor augmented IC-induced IL-1 production. The results suggest that IC are involved in stimulating IL-1 production by PBM and thus play a role in the immune response in GN.

A nephritogenic rat monoclonal antibody to mouse aminopeptidase A. Induction of massive albuminuria after a single intravenous injection

Antibodies directed against antigens present on renal epithelial cells can cause membranous glomerulonephritis in experimental animals, which closely resembles the human form of this disease. However, most antibodies produced so far fail to cause the persistent and severe proteinuria that is seen in humans. In our search for new antibodies of this kind, we have now produced a monoclonal antibody (mAb) against mouse aminopeptidase A, a hydrolase that is present in the mouse kidney. The mAb (ASD-4) was prepared by fusion of mouse myeloma cells with splenocytes of Lou rats immunized with brush border (BB) membranes from mouse kidneys. ASD-4 is of the IgG1 subclass and reacts with a 140-kD protein as demonstrated by immunoprecipitation on radiolabeled BB membranes. In indirect immunofluorescence and immunoelectronmicroscopy of normal mouse kidneys, ASD-4 was diffusely present on the BB of the S1 and S2 segments of the proximal tubules, and on the cell membranes of the glomerular visceral epithelia. It also bound to cell membranes of nonglomerular endothelia, smooth muscle cells of arteries, and juxtaglomerular cells. After injection of ASD-4 into normal mice, an immediate homogeneous binding to the capillary wall was seen that gradually changed into a fine granular pattern after 1 d. This glomerular binding was followed by binding to the BB and basolateral membranes of the convoluted proximal tubules. Immediately after injection of ASD-4, a dose-dependent albuminuria occurred that lasted for at least 16 d. ASD-4 is thus a new rat mAb against a well-defined renal epithelial antigen that causes not only membranous glomerulonephritis after a single injection in the mouse, but also severe albuminuria.

The contribution of antibody-mediated cytotoxicity and immune-complex formation to tubulointerstitial disease in passive Heymann nephritis

Passive Heymann nephritis (PHN), an experimental model of membranous nephropathy, is produced by Fx1A antiserum, which also reacts with antigens on the brush border (gp 330) and basolateral membrane (gp 90) of proximal tubules. We examined tubulointerstitial disease in PHN, identifying two distinct processes occurring on the luminal and basolateral membranes, respectively. Injected antibody bound diffusely to the tubular brush border from Day 1 to Day 7, followed by sloughing of microvilli and tubular-cell regeneration. Fine granular deposits of Fx1A antibody were present along the basolateral cell membrane by Day 1. These deposits rearranged in situ, enlarged, and became more focally distributed along tubular basement membranes (TBM). Interstitial inflammation, dominated by macrophages (Ia+, ED-1+) in association with a smaller number of T-cytotoxic cells (OX19+, OX8+) began by Day 3, reached peak intensity and persisted throughout the autologous phase (to Day 21). The distribution of focal clusters of interstitial macrophages predominately in association with TBM-immune deposits was demonstrated. Complement depletion prevented proteinuria but TBM deposits developed and the interstitial inflammation was unchanged. All aspects of the tubulointerstitial disease were amplified by a second injection of Fx1A antiserum. In vitro, Fx1A antibody bound to the surface of isolated proximal tubular epithelial cells and redistributed to form clusters of immune aggregates. Anti-Fx1A-induced cytotoxicity of tubular cells was demonstrated by prelabeling cells with 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The degree of cytotoxicity was dependent on complement concentration and the duration of incubation at 37 degrees C. PHN induced by Fx1A antiserum causes tubular-cell injury following interactions with brush-border antigens and TBM immune-complex disease associated with interstitial inflammation. These findings may be relevant to the acute and chronic interstitial disease of human membranous nephropathy.

Progressive glomerular injury after recovery from acute glomerulonephritis in rats

To determine if an acute immunologic injury resembling poststreptococcal nephritis could lead to chronic renal injury, rats with immune-complex glomerulonephritis produced with cationic human gammaglobulin were followed for 48 weeks. During Week 1, animals developed severe proteinuria, hypoalbuminemia, and a diffuse proliferative/exudative glomerulitis. Substantial recovery, characterized by a significant decline in urinary protein excretion and normalization of plasma albumin concentration, occurred by Week 4. Subsequently, rats developed significantly elevated blood pressures and increasing proteinuria. Glomerular histology at Week 48 revealed minimal inflammation, significant hypertrophy, and considerable sclerosis. We conclude that chronic, progressive renal disease can evolve after apparent recovery from an acute immunologic insult. Further study of this model should provide clinically relevant information about the mechanisms underlying this process.

Induction of unresponsiveness to Heymann's nephritis: inhibited by monoclonal antibody to CD4 but not to CD8

The effects of mAb therapy to CD4 or CD8 on induction of unresponsiveness to Heymann's nephritis by preimmunization with renal tubular antigen in IFA. Anti-CD4 mAbs (MRC Ox35) given for 2 weeks after RTA/IFA completely prevented the induction of resistance to HN, all rats developing proteinuria as well as high titers of autoantibody and Ig and C deposits in glomeruli. Anti-CD8 mAbs (MRC Ox8) did not prevent induction of unresponsiveness, even though it totally depleted CD8+ cells. In control rats not preimmunized with RTA/IFA, mAb therapy did not suppress disease induction, but in the case of anti-CD4 therapy enhanced the severity of disease. Persistent depletion of T cell subsets or complement components did not explain the effects of mAb therapy. These studies suggest that CD4+ cells are critical for the induction of unresponsiveness to HN and that therapy with mAb to CD4 can prevent induction of tolerance to an antigen, which has implications for its use in the induction of tolerance.

The complement-inhibiting protein, protectin (CD59 antigen), is present and functionally active on glomerular epithelial cells

Protectin (CD59 antigen) is a 20-kD phosphatidyl-inositol-linked membrane protein that inhibits formation of the membrane attack complex (MAC) of complement on homologous cells. Although the antigen has been identified in a number of human tissues, until recently a functional role had been demonstrated only in circulating cells. Using immunofluorescence techniques we have shown the presence of protectin on human glomerular epithelial cells (GEC) in culture and on GEC, tubular epithelial cells and endothelial cells in frozen sections of normal human renal cortex. In addition, we present evidence that this protein functions in protection of GEC from homologous complement: cultured cells incubated with the Fab2 fragment of a monoclonal anti-protein antibody were markedly more susceptible to killing by homologous serum than were cells in the absence of Fab2 anti-protectin. These findings suggest that this protein may be important in the maintenance of glomerular integrity in vivo, and may be of relevance in certain renal diseases.

Studies on antinephritic effect of TJ-8014, a new Japanese herbal medicine (4): Effects on accelerated passive Heymann nephritis in rats

We investigated the antinephritic effect of TJ-8014, in comparison to dipyridamole, on accelerated passive Heymann nephritis in rats. TJ-8014 (4.0 g/kg/day, p.o.) given from the heterologous phase (from the day of injection of the antiserum against Fx1A) markedly inhibited the urinary protein excretion and the elevation of plasma cholesterol levels as well as glomerular histopathological changes. When the treatment was started from the autologous phase (from the 22nd day) after proteinuria was fully developed, TJ-8014 also showed a beneficial effect. Dipyridamole (0.4 g/kg/day, p.o.) had no effect when the treatment was started either from the heterologous or autologous phase. TJ-8014 decreased glomerular rat IgG and rat C3 deposits, although it affected neither the plasma antibody titer against rabbit gamma-globulin nor the plasma complement level. TJ-8014 markedly prevented the reduction of plasma and adrenal corticosterone level as well as the reduction of renal blood flow of rats with nephritis. These results suggest that TJ-8014 may be a useful drug against idiopathic membranous nephropathy and the beneficial effect of this drug may be caused by the elimination of glomerular immune deposits and C3 through the increase in renal blood flow related to the enhanced release of adrenal corticosterone.

Membranous nephropathy in childhood and its treatment

Membranous nephropathy is predominantly a disease of middle-aged and elderly individuals, and is thus rather an uncommon finding in proteinuric and nephrotic children. In children, it differs in several important respects from the disease as seen in adults: an apparent associated cause is more common, macroscopic haematuria is seen quite frequently, a relapsing course is more often noted, renal venous thrombosis is not found and evolution into renal failure is the exception. Nevertheless, a proportion of children with membranous nephropathy do evolve into renal failure, and their management is discussed with particular reference to recent papers on the treatment of membranous nephropathy in adults. An aggressive search for associated disease is worthwhile in children, and one should wait to see what the evolution or proteinuria and renal function may be. If a progressive course becomes evident, then a trial of treatment with corticosteroids is worthwhile, but if this is ineffective then a more aggressive approach involving the use of alkylating agents may be justified. It remains undetermined what the best regime in children and adolescents may be.