The pathogenic antigen of Heymann nephritis is a membrane glycoprotein of the renal proximal tubule brush border

Loss of antigens associated with the apical endocytotic pathway in proximal tubules from rats with heymann nephritis

In addition to the glomerular lesions associated with Heymann nephritis, a rat model of human membranous nephritis, proximal tubule damage, and a perturbation of proximal tubule function also have been reported to occur in this disease. The aim of the present study was to examine in more detail the nature of the apical plasma membrane damage in proximal tubules using specific antibodies directed against clathrin, gp330, and a proton-pumping adenosine triphosphatase, all of which are components of the apical endocytotic apparatus of these epithelial cells. Immunocytochemical studies revealed a marked reduction in staining for all three antigens in proximal tubules from rats with active Heymann nephritis. Furthermore endocytotic uptake of intravenously injected FITC-dextran was considerably lower in diseased animals than in normal rats. Gp330 and rat IgG were identified as components of the luminal debris that accumulated during the course of Heymann nephritis. These results show that perturbation of proximal tubule endocytosis occurs in Heymann nephritis together with a loss of three apical antigens that are normally localized on membrane domains associated with the apical endocytotic pathway in these cells. The results also suggest that antibody-antigen complexes may be shed from the plasma membrane in both the glomerulus and the proximal tubule in this disease.

Circulating anti-entactin antibodies in patients with glomerulonephritis

Sera from 305 consecutive patients in a renal biopsy series were analyzed for the presence of anti-entactin antibodies by ELISA. Of these patients, 59% had primary glomerulonephritis, 21% had secondary glomerulonephritis, while 20% had other nephropathies (noninflammatory conditions like amyloidosis, diabetic nephropathy, nephrosclerosis, etc.). Forty-one of these patients (13.4%) were positive for IgG/IgM antibodies against entactin: 60% of them had primary glomerulonephritis, 35% had secondary glomerulonephritis, while the remaining 3 patients had other nephropathies. Fifteen (70%) of the 23 patients with primary glomerulonephritis had proliferative glomerulonephritis (PGN), whereas 13 (87%) of the 15 patients with secondary glomerulonephritis were due to systemic connective tissue diseases (SCTD): 7 due to SLE, 4 due to SLE like SCTD and two due to other SCTD. There was a peak of incidence corresponding to the group aged 18 to 30 years. A majority of these patients (12 of the total 17) had primary glomerulonephritis and were associated with nephrotic or subnephrotic grade proteinuria, poorly or nonresponsive to immunosuppressive treatment and associated, in several cases, with progressive deterioration of renal function. In addition, there was a tendency to another peak in the age group 51 to 60 years. Most of these patients (6 of the total 8) had glomerulonephritis secondary, mainly, to SLE or SLE like SCTD with milder degree of proteinuria and better preserved renal functions. Anti-entactin antibodies were not found in certain glomerulonephritides like IgA nephropathy and those secondary to systemic vasculitides and in control subjects (healthy subjects, and patients with a variety of non-renal disorders including inflammatory diseases).(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary excretion of the C5b-9 membrane attack complex of complement is a marker of immune disease activity in autologous immune complex nephritis

The urinary excretion of the C5b-9 membrane attack complex of complement correlates with glomerular deposition of antibody in the passive Heymann nephritis (PHN) model of membranous nephropathy (MN). To determine if this parameter can be correlated with antibody deposition in a model of MN induced by an autologous mechanism and thus more analogous to human MN, the relationship of urinary C5b-9 to ongoing glomerular immune complex formation late in autologous immune complex nephritis (AICN) was studied. Based on urinary C5b-9, the animals were divided into two groups at 12 weeks after induction of AICN, those with persistently high urinary C5b-9 excretion and those in whom urinary excretion of C5b-9 returned to undetectable levels. While all rats developed glomerular deposition of rat IgG and significant proteinuria, high C5b-9 excretors had greater proteinuria and prolonged positive staining for glomerular C3. When normal syngeneic kidneys were transplanted into rats (n = 3) from each group, only those with persistent C5b-9 excretion developed subepithelial immune deposits of rat IgG in the transplanted kidney. As in the PHN model of MN, proteinuria was dissociated widely from urinary C5b-9 excretion, glomerular C3 staining, and evidence of circulating antibody. Thus these findings demonstrate that urinary excretion of C5b-9 serves as an index of on-going immunologic disease activity in the AICN model of MN, while proteinuria does not.

Definition of glomerular antigens by monoclonal antibodies produced against a human glomerular membrane fraction

Experimental animal models of glomerulonephritis (GN) produced by direct antibody binding to non-basement membrane glomerular capillary wall antigens do not to date have human parallels. To examine the potential for this form of humoral glomerular injury in man, we sought to define discrete human non-GBM glomerular antigenic targets using hybridoma technology. Mice were immunised intraperitoneally with 20-100 micrograms of a human glomerular membrane fraction (HGMF). Six fusions have yielded 12 stable reagents defined by positive glomerular indirect immunofluorescence (IF) and microELISA using HGMF as the screening antigen. Subclass analysis of ascitic McAbs indicated several IgG1, one IgG2b, and three IgM reagents. Distinctive IF patterns of reactivity with epithelial, endothelial or mesangial structures have been observed, with or without peritubular capillary, tubular basement membrane and vessel wall reactivity. Seven normal non-renal human organs and the kidneys of rat, rabbit and sheep have shown patterns characteristic of each individual McAb, restricted to human or with species cross reactivity. To partially characterise McAb-reactive antigens, detergent-solubilised renal cortex and collagenase-solubilised GBM (CS-GBM) extracts have been probed by immunoblot. A unique McAb 7-5Q, reactive with glomerular and tubular epithelial structures, binds major bands of approximately 107 KD and 93 KD in detergent solubilised cortex and a single band of similar size by immunoprecipitation (110 KD). 5-3A (a human-restricted linear-reacting McAb) binds bands of 20-200 KD (major band 58 KD) in CS-GBM. In conclusion, distinct species-restricted and more broadly disposed glomerular epitopes are definable in man by McAbs and are potential targets for humoral injury. Purification of these antigens will allow assay for circulating putative nephritogenic auto-antibody and potentially, McAbs may be useful in screening urine for evidence of occult structural renal disease.

Monoclonal antibodies against membrane proteins of the rat glomerulus. Immunochemical specificity and immunofluorescence distribution of the antigens

Monoclonal antibodies (MAbs) were generated to detergent-solubilized glomerular extracts to identify new epithelial and endothelial membrane proteins and to study the possible role of the corresponding antigens in the formation of immune deposits. Triton X-114 extracts of isolated glomeruli were subjected to phase separation, and the resultant detergent and aqueous phases were used to immunize mice. Monoclonal antibodies were prepared by standard techniques, and hybridomas secreting antibodies (IgGs) that recognize glomerular cell surface antigens were selected by enzyme immunoassay (EIA) and indirect immunofluorescence. The IgGs of 13 MAbs selected for study recognized antigens of different molecular weights (45-350 kd) by immunoprecipitation and immunoblotting and had different distributions in the glomerulus and in other renal structures by immunofluorescence. Several proved to recognize known antigens--ie, podocalyxin (MAbs 1A, 5A, 11A, and 20A), gp330 (20B), and dipeptidylpeptidase IV (26C). Others recognized antigens not previously characterized that fell into four groups: 1) those that were detected mainly in glomeruli; 2) those present in both glomeruli and peritubular capillaries; 3) those present in both glomeruli and tubule epithelia; and 4) those detected in all these sites. The pattern of glomerular staining also varied, but most of the antigens appeared to be expressed on either the endothelium or the epithelium, or on both. 27A IgG was specific for podocytes and weakly precipitated a 103-kd protein. 7A and 13A IgG precipitated a 120-kd protein and stained glomeruli as well as the basal aspects of distal tubules. 23A IgG recognized a more-than 350-kd antigen that appeared to be specific for endothelial cells in rat kidney and in all other organs studied. 14A IgG precipitated a 150-kd protein and stained glomeruli, proximal tubule brush borders, and endothelial and epithelial cells in rat kidney and in several other organs. 4B and 9B IgG gave a granular cytoplasmic staining in all cells. When injected intravenously into rats, all of the MAbs except 4B and 9B rapidly bound to glomeruli, demonstrating that the respective antigens are exposed at the cell surface and represent potential targets for antibody-mediated immune injury. It is concluded that selective detergent extraction of glomeruli is a useful approach for generation of antibodies that recognize native, nondenatured membrane components of glomerular endothelial and epithelial cells.

Entactin: a possible auto-antigen in the pathogenesis of non-Goodpasture anti-GBM nephritis

It has recently been demonstrated that many patients with various types of glomerulonephritis have antibodies to the 6M guanidine-HCl extract of glomerular basement membrane (Bygren et al, Nephrol Dial Transplant 4:254-261, 1989). In the present study a 150 K protein was isolated from the guanidine extract of bovine glomerular basement membrane utilizing ion exchange and gel filtration chromatographic procedures. Amino acid analysis and size of the isolated protein revealed similarity to that of entactin/nidogen. The identity of this protein as entactin/nidogen was further suggested by its precipitation with two different antibodies in a radioimmunoassay and by its reaction with four different antibodies in a sandwich ELISA. Inhibition of the antibodies to 150 K by bovine entactin, which was isolated separately and sequenced for amino acids, confirmed the identity of the 150 K protein as entactin/nidogen. Furthermore, it was shown that about one third of those patients who show antibodies to the crude guanidine extract have circulating antibodies directed against entactin. This was further confirmed by the competitive inhibition of antibodies to the crude guanidine extract in one of the positive serum by entactin in an ELISA inhibition and by immunoblotting experiments. These observations propose entactin as a possible non-Goodpasture glomerular basement membrane antigen that could be involved in the pathogenesis of certain forms of autoimmune glomerulonephritis (non-Goodpasture anti-GBM glomerulonephritis) in man. Most of these patients have a granular pattern of the immunoglobulin deposition along the glomerular basement membrane. This suggests the possibility that anti-GBM glomerulonephritis in human beings can have non-linear immunoglobulin deposits along the GBM.

Molecular cloning of a cDNA encoding a major pathogenic domain of the Heymann nephritis antigen gp330

Heymann nephritis is an experimental autoimmune disease in rats that is characterized by accumulation of immune deposits (IDs) in kidney glomeruli. The disease is initiated by the binding of circulating antibodies to a membrane glycoprotein, gp330, which is a resident protein of clathrin-coated pits on glomerular epithelial cells (podocytes). We have defined a domain representing about 10% of gp330 that appears to be responsible for the formation of stable glomerular IDs. A cDNA clone (clone 14) was isolated from a rat kidney cDNA expression library by screening with IgG eluted from glomeruli of rats in early stages (3 days) of passive Heymann nephritis. The clone 14 cDNA contains an open reading frame encoding the C-terminal 319 amino acids of gp330. The predicted amino acid sequence contains four internal repeats of 11 amino acids, which are also found in the putative ligand-binding region of carbohydrate-binding lectin-like receptors. An antibody raised against the clone 14 fusion protein recognized gp330 by immunoblotting and induced formation of subepithelial IDs typical of passive Heymann nephritis when injected into normal rats. When the clone 14 fusion protein was used to immunize rats, subepithelial IDs of active Heymann nephritis were found after 12 weeks. No IDs were formed by active or passive immunization of rats with fusion proteins derived from other regions of gp330. These results demonstrate that clone 14 encodes a region of gp330 responsible for antibody binding and ID formation in vivo.

Cell type-specific post-Golgi apparatus localization of a "resident" endoplasmic reticulum glycoprotein, glucosidase II

Glucosidase II, an asparagine-linked oligosaccharide processing enzyme, is a resident glycoprotein of the endoplasmic reticulum. In kidney tubular cells, in contrast to previous findings on hepatocytes, we found by light and electron microscopy immunoreactivity for glucosidase II predominantly in post-Golgi apparatus structures. The majority of immunolabel was in endocytotic structures beneath the plasma membrane. Immunoprecipitation confirmed presence of the glucosidase II subunit in purified brush border preparations. Kidney glucosidase II contained species carrying endo H-sensitive, high mannose as well as endo H-resistant oligosaccharide chains. Some species of glucosidase II contained sialic acid. The sialylated species were enzymatically active. This study demonstrates than an enzyme presumed to be a resident of the endoplasmic reticulum may show alternative localizations in some cell types.

Pathogenesis of experimental lupus nephritis: a role for anti-basement membrane and anti-tubular brush border antibodies in murine chronic graft-versus-host disease

The pathogenesis of renal involvement was studied in murine chronic graft-versus-host disease (GVHD), which is a model for human systemic lupus erythematosus. GVHD was induced by four i.v. injections of lymphocytes from DBA/2 donor mice into (C57BL/10 x DBA/2)F1 hybrids at 3-4-day intervals. Two weeks after the first injection, antibodies were found to have been deposited in the mesangium and along the glomerular basement membrane (GBM) in a linear arrangement, which changed to a granular pattern after 6-8 weeks. In this stage, large electron-dense complexes were present both subepithelially and subendothelially along the GBM. Proteinuria increased up to 11,300 +/- 2140 micrograms/18 h. Indirect immunofluorescence studies and ELISA showed that sera and kidney eluates contained autoantibodies directed against nuclear antigens and GBM component laminin as well as against renal tubular epithelial antigens (RTE). The specificity of the anti-RTE antibodies was further characterized by the use of absorption techniques as well as immunoblotting. The early linear immunofluorescence pattern seems to be associated with glomerular binding of anti-GBM antibodies, while electron-dense complex formation in later stages may be induced by the superimposed deposition of anti-RTE antibodies. Similar phenomena were recently described in Heymann's nephritis in the rat, a model for human membranous nephropathy.

Experimental glomerulonephritis induced in rats by a lectin and its antibodies

The aim of the present study was to investigate the events following interaction of antibody with an antigen planted on the surface of glomerular endothelial cell (GEN). A lectin, Helix pomatia agglutinin (HPA), was planted at the surface of rat GEN by the perfusion of the isolated left kidney with neuraminidase (NRD) and HPA. A subsequent perfusion with IgG fraction, but not with Fab fragments, of rabbit anti-HPA serum induced formation of granular immune deposits (IDs) on the surface of GEN. When the left kidney was revascularized after initial formation of IDs, acute glomerulonephritis ensued. Fifteen minutes after revascularization, granular IDs were observed at the subendothelial space. Two days later, there was decrease of subendothelial IDs with concomitant appearance of subepithelial IDs. At the seventh day, IDs were mainly localized in the subepithelial space. The results suggest that this model of experimental glomerulonephritis is characterized by: (1) initial formation of HPA immune complexes (ICs) at the surface of GEN; and by (2) subsequent movement of ICs from luminal side to subepithelial area with local formation of IDs. The results are relevant to the understanding of the kinetics of ICs resulting from interaction of antibodies with exogenous antigens "planted" in the glomerular capillary walls, and of the local formation of IDs.

Thymocytes reacting with heterologous antibodies against GP 330 in autologous immune complex glomerulopathy (AICG) in the rat. The relation between susceptibility for AICG and anti-GP 330-binding thymocytes

Autologous immune complex glomerulopathy (AICG) is induced by immunizing rats with a crude brushborder fraction of rat kidney tubules (Fx1A) or with the purified GP 330 antigen. In these animals, anti-brushborder antibodies develop, leading to subepithelial immune complexes along the glomerular capillary wall. In rats with AICG, thymocytes sensitized against Fx1A as well as thymocytes recognizing anti-Fx1A are present. These latter cells might play a role in the specific tolerance against the pathogenetic antigen GP 330. To substantiate this notion, immunofluorescence studies were performed in which the number of anti-GP 330 binding cells was quantified in thymus cell suspensions of rats with AICG, in control rats and in naive rats with different genetic background. It is shown that increased numbers of anti-GP 330-binding thymocytes in rats with AICG are associated with a decline in the serum anti-brushborder titer. Furthermore, it appears that the number of anti-GP 330-binding thymocytes in naive rats of the non-responder Brown Norway strain is significantly higher as compared to the PVG/c and Lewis strains, which are susceptible for AICG. The correlation between the numbers of anti-GP 330-binding thymocytes and the susceptibility for AICG suggests a role for these cells in maintaining the tolerance against the Fx1A (GP 330) antigen.

Colchicine-induced redistribution of an apical membrane glycoprotein (gp330) in proximal tubules

Factors governing the selective, polarized insertion of membrane proteins are poorly understood, but some studies have suggested that microtubules are involved in the generation and maintenance of cell polarity. We have examined by immunocytochemistry the effect of the microtubule-disrupting agent, colchicine, on the cellular distribution of an endogenous glycoprotein, gp330, which is normally inserted only into the apical plasma membrane of proximal tubule epithelial cells. In control rats, gp330 was localized in the brush border and in apical invaginations and vesicles. Six hours after injection of colchicine, however, vesicles containing gp330 were dispersed throughout the entire cytoplasm of the cell. Many vesicles were packed into basolateral infoldings, close to the plasma membrane, but there was no significant insertion of gp330 into the basolateral membrane. When rabbit anti-gp330 antiserum was injected intravenously into colchicine-treated rats, immune complexes appeared in the glomerular basement membrane but could not be detected in peritubular basement membranes. This supports the conclusion that colchicine treatment does not result in the insertion of gp330 into the basolateral plasma membrane of proximal tubule cells. Our results indicate that although microtubules are involved in the accumulation of gp330-containing vesicles at the apical pole of the cell, other factors must be required for fusion with the plasma membrane to occur.

Urinary excretion of C5b-9 reflects disease activity in passive Heymann nephritis

Passive Heymann nephritis (PHN) is a model of membranous nephropathy in rats in which glomerular injury is mediated by the terminal C5b-9 membrane attack complex of complement. This model has been shown to be associated with markedly elevated urinary excretion of C5b-9, compared to other experimental models of glomerulonephritis To determine if urinary C5b-9 excretion could serve as an index of disease activity by correlating with the formation and quantity of glomerular subepithelial immune deposits in PHN, we measured urinary excretion of C5b-9 in PHN under several experimental conditions. In the heterologous phase a direct correlation was demonstrated between levels of urinary C5b-9 excretion and the amount of anti-Fx1A IgG deposited in glomeruli (r = 0.85). In the autologous phase, C5b-9 excretion correlated with the amount of deposit forming antibody present in the serum and resolved when antibody disappeared, despite persistence of glomerular deposits of antigen, antibody, C5b-9 and heavy proteinuria. Glomerular C3 deposits paralleled urinary C5b-9 excretion. Re-initiation of active deposit formation by a second injection of anti-Fx1A produced new C3 deposits and a marked rise in C5b-9 excretion. Finally, complete abrogation of deposit formation by transplanting PHN kidneys into normal recipients also halted C5b-9 excretion. Our findings demonstrate that urinary excretion of C5b-9 is a sensitive index of on-going immunologic disease activity in the PHN model of membranous nephropathy.

Preparative polyacrylamide gel electrophoresis in the isolation of the nephritogenic proteins of passive Heymann nephritis

To study kidney antigens involved in the formation of glomerular subepithelial immune deposits in passive Heymann nephritis polypeptides of 500, 130 and 105 kDa were isolated from rat kidney brush border (BB) membrane fraction using preparative polyacrylamide gel electrophoresis. Polyclonal antibodies raised against these proteins were specific for their respective antigens in immunoblotting. All three antisera bound to proximal tubular BB of kidney and to apical surfaces of several other epithelia as shown by indirect immunofluorescence on frozen sections of normal rat tissues. The anti-500 kDa and anti-105 kDa, but not the anti-130 kDa, antibodies also stained glomeruli and the anti-105 kDa antibodies also endothelial cells. After injection into rats the anti-500 kDa IgG bound to kidney glomeruli forming diffuse, granular deposits of rabbit IgG along the glomerular capillary walls, as shown by direct immunofluorescence. In electron microscopy the immune deposits were subepithelial and electron dense. The deposits remained in glomeruli for at least 60 days and increased with time. Deposits of C3 were not detected and proteinuria did not develop. The anti-130 kDa and the anti-105 kDa IgGs did not form glomerular deposits after in vivo injections. The results suggest that the 500 kDa and the 105 kDa proteins or related antigens are present in glomeruli and the 500 kDa protein is located on the epithelial side of the glomerular basement membrane. Circulating antibodies can bind to the 500 kDa protein forming immune complexes which rearrange and form electron dense deposits. The results further demonstrate that preparative gel electrophoresis is a useful technique for the isolation of kidney proteins of immunopathologic interest.

Studies with antibodies to cultured rat glomerular epithelial cells. Subepithelial immune deposit formation after in vivo injection

To investigate the role of glomerular epithelial cell (GEC) membrane proteins in the in situ formation of subepithelial immune deposits, the authors raised a rabbit antiserum against GEC that had been grown in culture (anti-GEC). By indirect immunofluorescence (IF) on normal rat kidney, anti-GEC stained proximal tubular brush border (BB). After intravenous injection into animals, granular glomerular capillary wall staining for IgG was present by IE and subepithelial immune deposits were identified by standard transmission and immunoelectron microscopy. Using the latter technique, injected anti-GEC IgG was identified beneath slit diaphragms and in endocytic-coated pits and intracellular vesicles of podocytes. Anti-GEC immunoprecipitated gp330 and two other proteins from radiolabeled BB. These proteins also were identified by sheep anti-rat Fx1A, the antiserum responsible for passive Heymann nephritis. Anti-GEC and anti-Fx1A also immunoprecipitated five identical proteins from surface-labeled GEC. Biosynthetically-labeled but not surface-labeled GEC contained immunoprecipitable gp330. Thus, injection into rats of antibodies raised against cultured GEC can produce subepithelial immune deposits, a disease process classically induced by antibodies to BB or its purified components. In addition to gp330, GEC and BB share other antigenic determinants that may contribute to the formation of these immune deposits.

Role of dipeptidyl peptidase IV (gp 108) in passive Heymann nephritis. Use of dipeptidyl peptidase IV-deficient rats

Injection of antibodies to renal tubular membrane (Fx1A) into Lewis rats induces granular deposits of IgG in glomeruli and proteinuria (passive Heymann nephritis, PHN), and similar lesions are also induced by antibody to one of the antigens in Fx1A, dipeptidyl peptidase IV (DPP IV, gp 108). In this study, the role of DPP IV in PHN was investigated using DPP IV-deficient F344 rats. The amount of DPP IV found in F344 rat kidneys was less than 0.05% of that present in Wistar rats, and injection of anti-DPP IV antibody into F344 rats did not induce proteinuria. Injection of anti-F344 Fx1A rabbit antibodies that contain no detectable anti-DPP IV antibody into Lewis or F344 rats induced PHN, characterized by granular deposits of rabbit IgG in glomeruli and massive proteinuria, although the appearance of proteinuria was delayed in comparison with that occurring in response to injection of anti-Wistar Fx1A antibodies. These results indicate that DPP IV may contribute to, but is not essential for, the induction of PHN.

Increased urinary excretion of C5b-9 distinguishes passive Heymann nephritis in the rat

Increased urinary excretion of C5b-9 distinguishes passive Heymann nephritis from other forms of experimental glomerulonephritis in the rat. In the passive Heymann nephritis (PHN) model of membranous nephropathy (MN) subepithelial deposits form from anti-Fx1A antibody reacting with antigen expressed on the glomerular epithelial cell membrane followed by membrane patching and shedding of immune complexes. Immune complex deposits are accompanied by deposits of C5b-9 which is required for the mediation of proteinuria. We tested the hypothesis that C5b-9 assembly on the epithelial cell membrane might result in C5b-9 excretion in the urine, which would distinguish this autoimmune mechanism of MN from other processes that result in subepithelial immune complex deposits. Using monoclonal antibodies developed to rat C6 and a rat C5b-9 neoantigen, in a sensitive ELISA assay, elevated urinary excretion of rat C5b-9 was documented in PHN associated with on-going glomerular immune deposit formation. No urinary C5b-9 was detectable in MN induced by an exogenous antigen (cationized IgG) despite equivalent glomerular C5b-9 deposits, or in models of nephrotoxic nephritis, subendothelial immune complex nephritis, anti-mesangial cell membrane antibody-induced nephritis or two non-immune nephropathies. Infusion of preformed C5b-9 in proteinuric animals excluded glomerular filtration of C5b-9 as a contributing mechanism to urinary C5b-9 excretion. We conclude that in the rat, increased urinary excretion of C5b-9 is a marker of MN induced by antibody to a glomerular epithelial cell antigen. Urine C5b-9 excretion reflects active glomerular immune deposit formation and distinguishes MN induced by this mechanism from other forms of MN as well as from other glomerular diseases with equivalent glomerular C5b-9 deposits.

The specificity of nephritogenic antibodies. V. Glomerular localization of anti-GP 330 and anti-GP 90 antibodies present in passive Heymann serum

Administration in the rat of rabbit antibodies directed against rat tubular brushborder antigens (FXIA) leads to membranous glomerulopathy (HICN) associated with glomerular immune complexes (ICXS). These anti-FXIA antibodies (Abs) contain two major specificities, anti-GP 330 and anti-GP 90. The contribution of each specificity to the localization of anti-FXIA Abs was studied by direct immunofluorescence. Perfusion studies, under conditions which avoid ischaemia, confirmed that in this system glomerular localization of anti-FXIA Abs depends only on anti-GP 90 Abs, and the failure of anti-GP 330 Abs to localize after perfusion could not be attributed to ischaemia. In contrast, intravenous (i.v.) injection of anti-GP 330 Abs results in granular deposits of rabbit IgG, similar to those observed using anti-FXIA Abs. Injection i.v. of anti-GP 90 Abs results only in (faint) linear deposits. Using alternating and combined perfusion studies with these Abs, it is shown that anti-GP 90 Abs do not influence localization of anti-GP 330 Abs. In addition, systemic administration of anti-GP 90 Abs combined with perfusion of anti-GP 330 Abs does not facilitate localization of anti-GP 330 Abs. Although directly after i.v. injection of anti-FXIA Abs some anti-GP 90 Abs probably localize in the glomerular capillary wall, our results exclude a dominant or ancillary role for anti-GP 90 Abs in the formation of glomerular Icxs in HICN.

Nephritogenicity of proteoglycans. III. Mechanism of immune deposit formation

Administration of antibody, directed against glomerular basement membrane (GBM) heparan sulfate-proteoglycan, into a presensitized rat results in the induction of membranous nephropathy with subepithelial immune-complex deposits. In this investigation, we examined the mechanisms responsible for the formation of subepithelial immune-complex deposits in the anti-HS-PG model. In initial experiments, the intravenously administered radioiodinated antibody was seen exclusively localized in the regions of the glomerular capillary wall where the subepithelial deposits were observed. To determine their exclusive localization in the subepithelial space, kinetics of movement of the intravenously administered antibody was investigated. The antibody localized in the inner layers of the GBM within a few minutes after its administration. It equilibrated in the inner and outer layers of the GBM in a matter of a few hours. Then, after 24 hours, it gradually disappeared from the inner layers of the GBM and persisted in the outer layers only. The ready clearance of the antibody from the inner layers may be related to the differential in the kinetics of lateral intrinsic plasma fluid currents within the GBM. The persistence of heterologous antibody exclusively in the outer layers and the availability of host autologous antibodies probably resulted in the development of immune complex deposits in the subepithelial space. The glomeruli devoid of plasma water currents showed no change in the concentration of the antibody in the inner and outer layers of the GBM or mesangial matrix. Also, no antibody binding was observed with the plasmalemma of either the foot processes or visceral epithelia. The data suggest that the biochemical-biophysical properties of the glomerular capillary wall, in concert with its intraglomerular hemodynamics, most likely played a significant role in the development of subepithelial immune-complex deposits in this model.

Monoclonal autoantibodies specific for kidney proximal tubular brush border from mice with experimentally induced chronic graft-versus-host disease

Nine hybridomas producing monoclonal autoantibodies specific for kidney proximal tubular brush border were found in 600 hybridomas derived from (C57BL/6J X DBA/2)F1 mice injected with DBA/2 T cells. None of the 1100 hybridomas derived from nonautoimmune (C57BL/6J X DBA/2)F1 mice produced antibodies with a similar specificity. Four of these nine monoclonal antibodies were characterized further. They did not bind to cryosections of liver, lung, stomach, or intestine. Three bound to kidney proximal tubular brush border of mouse, cattle, sheep, pigs, rabbits, rats, and humans, whereas the fourth was specific only for murine brush border. All four precipitated from mouse kidney microvilli, a protein with an apparent molecular weight of 160,000 under reducing as well as nonreducing conditions. Removal of asparagine-linked carbohydrate with EndoF reduced the molecular weight of the 160,000 protein by about 20,000. One of the three multi-species-specific antibodies bound to pig kidney aminopeptidase, a glycosylated enzyme located on the microvilli of kidney proximal tubular brush border. Three antibodies have a heavy-chain variable region encoded by VH genes of the J558 family, whereas the heavy-chain variable region of the fourth is encoded by a VH gene of the 7183 family. Attempts to passively transfer immune complex glomerulonephritis to normal mice by injection of the purified monoclonal antibodies or by growth of the corresponding hybridoma cells in mice have so far been unsuccessful. However, antibodies recognizing the 160,000 molecule are present in the serum of mice with chronic graft-versus-host disease and can be eluted from kidneys with immune complex glomerulonephritis.

Developmentally regulated expression of cell surface carbohydrates during mouse embryogenesis

Cell surface carbohydrates undergo marked alterations during mouse embryogenesis. In preimplantation embryos, many carbohydrate markers show stage-specific expression in diverse ways. In early postimplantation embryos, certain carbohydrate markers are localized in defined regions in the embryo. Important carriers of stage-specific carbohydrates are the lactoseries structure (Gal beta 1----4GlcNAc) and the globoseries structure (Gal alpha 1----4Gal). Notably, the glycoprotein-bound large carbohydrate of poly-N-acetyllactosamine-type ([Gal beta 1----4GlcNAc beta 1----3]n) carries a number of markers preferentially expressed in early embryonic cells. These markers are of practical value in analyzing embryogenesis and cell differentiation. For example, in order to monitor in vitro differentiation of multipotential embryonal carcinoma cells, stage-specific embryonic antigen-1 (SSEA-1) and the Lotus agglutinin receptor have been used as markers of the undifferentiated cells, and the Dolichos agglutinin receptor has been used as a marker of extraembryonic endoderm cells. Developmental control of cell surface carbohydrates is attained by controlled expression of activities of key glycosyltransferases; for example, the activity of N-acetylglucosaminide alpha 1----3 fucosyltransferase is lost during in vitro differentiation of embryonal carcinoma cells to parietal endoderm cells, in parallel to the disappearance of SSEA-1. Accumulating evidence suggests that poly-N-acetyllactosamine-type glycans that are abundant in early embryonic cells are involved in cell surface recognition of these cells.

Identification of gp108, a pathogenic antigen of passive Heymann nephritis, as dipeptidyl peptidase IV

Our previous paper showed that the glycoprotein of Mr 108,000 (gp108) is one of the major components of rat renal tubular brush border antigens and that an injection of anti-gp108 antiserum in rats induces passive Heymann nephritis with acute and severe proteinuria. In this study, gp108 was identified as a monomer of dipeptidyl peptidase IV (DPP IV). The anti-gp108 antibody was shown to immunoprecipitate DPP IV from Triton-extract of renal tubular membrane fractions. DPP IV was co-purified with gp108 from the Triton-extract by columns of DEAE-cellulose and Bio-gel A-1.5 m. The ratio of DPP IV activity and gp108 content was nearly constant throughout the purification steps. The final purified gp108 showed a high specific activity of DPP IV, comparable to that reported for purified rat DPP IV. These results indicate that gp108 is a monomer of DPP IV.

Quantitative and qualitative studies of antibody-induced mesangial cell damage in the rat

Intravenous administration of heterologous anti-rat thymocyte serum (ATS), which reacts with a Thy-1-like antigen present on rat glomerular mesangial cells, caused lytic (1 hr to 2 days), hypercellular (4 to 14 days), and sclerotic (2 to 3 months) mesangial lesions in Lewis rats. The normal control of 48.6 +/- 7.9 (mean +/- SD) glomerular nuclei on histologic section decreased significantly (P less than 0.001) to 39.8 +/- 6.1, 37.4 +/- 6.0, and 38.9 +/- 6.8 at one hour, four hours and two days after ATS administration, respectively. Thereafter glomerular nuclei increased to 54.7 +/- 11.5 (P less than 0.05) at four days, 62.5 +/- 9.6 (P less than 0.001) at one week and 64.1 +/- 14.2 (P less than 0.001) at two weeks, and normalized (P greater than 0.05) to 49.4 +/- 8.9 at one month and 50.6 +/- 9.0 at three months. By electron microscopy, glomerular damage in the lytic stage was restricted to mesangial cells and was manifested as hydropic degeneration or lysis. Rabbit IgG and rat C3 were found in the mesangium one hour after injection; they decreased at two days and were negligible at four days. By paired label isotope study, 11.6 micrograms of antibody bound per 7.6 X 10(4) glomeruli at one hour was needed to induce mesangial cell degeneration. No or only minimal changes in proteinuria and in serum creatinine were observed with the dosage used in this rat strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a 400-kd protein in the brush borders of human kidney tubules that is similar to gp330, the nephritogenic antigen of rat Heymann nephritis

The nephritogenic antigen of Heymann nephritis (HN)--a well-studied experimental rat model disease of human membranous glomerulonephritis (MGN)--was recently shown to be a 330-kd glycoprotein (gp330) which is present in the membranes of both the rat tubular brush borders and of podocytes. Because the pathogenic antigen(s) of MGN are unknown, the authors have searched for a gp330-like molecule in human kidney and for its role in MGN. The authors here report that a membrane protein (apparent molecular weight 400 kd) is present in human kidney which is immunologically cross-reactive with rat gp330. By immunoelectron microscopy (using rabbit anti-rat gp330 IgG or a monoclonal anti-400-kd IgG) this molecule is similarly localized in human proximal tubules, but it is absent from the podocytes of human glomeruli. The 400-kd molecule is not detected in the glomerular immune deposits of 30 biopsies of MGN. It is proposed that this is due to the lack of the 400-kd protein in human glomeruli which prevents the formation of initial 400-kd anti-400-kd IgG immune complexes in situ.

Immunopathogenetic mechanisms in renal disease

This review deals with various immunopathogenetic mechanisms of renal diseases. Although immune-complex nephritis was long thought to be the result of deposition of circulating immune complexes, recent studies have revealed the importance of in situ formation. In experimental Heymann nephritis, an antigen (gp 330) has been localized on glomerular epithelial cells, and antibodies reactive with gp 330 have been eluted from glomeruli; deposits appear to result from shedding of complexes from the podocyte surface into the basement membrane. In human disease, it seems likely that mesangial and subendothelial deposits most often result from deposition of circulating immune complexes, whereas subepithelial deposits are formed mainly in situ. Cell-mediated immune mechanisms are capable of producing glomerular injury, as shown in experimental models. In humans, Wegener's granulomatosis and idiopathic crescentic glomerulonephritis may involve such mechanisms. In certain forms of experimental and human tubulointerstitial nephritis, cell-mediated immunity also seems to play an important role.

Rat Heymann nephritis antigen is closely related to brushin, a glycoprotein present in early mouse embryo epithelia

Heymann nephritis is a glomerulonephritis induced in rat by injecting kidney extracts. The responsible antigen is known to consist of two high molecular weight glycoproteins, gp330 and gp300, located in renal tubular brush border cells. We show that rabbit antibodies made against purified rat gp330 react in immunofluorescence tests with several polarized epithelia present in pre- and post-implantation mouse embryos, as well as with murine trophoblastoma cells. Immunoprecipitation experiments demonstrate that anti-gp330 antibodies also recognize two components with relative molecular weights of 330 and 300 Kd in mouse embryonic cells. Furthermore, sequential immunoprecipitation experiments and limited proteolysis tests suggest that these two components are identical with brushin, a glycoprotein set known to be present in a mouse early embryonic epithelium and in adult kidney cells. Finally, ultrastructural studies demonstrate that anti-gp330 antibodies react with molecules preferentially located in coated pits of murine early epithelial cells. These results show that Heymann nephritis antigen has an embryonic counterpart closely related to, if not identical with, previously identified brushin glycoproteins. These molecules could be a receptor to an unknown ligand or a structural component of coated pit membrane.

Down modulation of Heymann's nephritis by mercuric chloride

The time course of Heymann's nephritis (HN), assessed on proteinuria and immunomorphology, has been compared in Lewis (LEW) rats immunized with BB alone (group A) or injected with HgCl2 and subsequently immunized in a similar manner (group B). Whereas all rats from group A developed typical HN characterized by heavy proteinuria and abundant glomerular immune deposits, rats from group B did not develop or developed a markedly attenuated form of HN; proteinuria was never detectable, immune deposits were absent or minimal. No abnormalities were found in rats injected with HgCl2 alone. In order to explain our findings, we have studied the glomerular and tubular expression of the 330 kD nephritogenic glycoprotein (gp330) as well as the corresponding antibody response. In rats receiving HgCl2, gp330 was normally expressed on BB and glomerular epithelial cells as indicated by in vitro and in vivo binding of anti-gp330 antibodies, but titers of anti-BB and anti-gp330 antibodies were considerably lower than in group A control rats. These findings therefore suggest that HgCl2 acts by its immunodepressive effect recently related to an increase in T suppressor cells. This effect is paradoxical since HgCl2 induces autoimmunity in Brown-Norway rats, and we suggest that it may be akin to observations reported in clinical practice where drugs may be immunostimulatory in some patients and immunodepressive in others. The mercury model may therefore represent a unique tool to evaluate the relationship between genetics and drug-induced immune dysregulation.

Heymann nephritis in rats induced by human renal tubular antigens: characterization of antigen and antibody specificities

An injection of human renal tubular fraction, Fx1A, with Freund's complete adjuvant in rats induces Heymann nephritis (HN) with clinical and morphological features similar to rat Fx1A-induced HN. The present study was undertaken to characterize antibody specificities and the corresponding antigen involved in human Fx1A-induced HN. In sera of rats immunized with human Fx1A, not only anti-human Fx1A antibody but also antirat Fx1A antibody was detected by enzyme immunoassay. Eluted antibody from the glomeruli also showed both activities. In an inhibition study of enzyme immunoassay, binding of the eluted antibody to human Fx1A was inhibited by both human and rat Fx1A and also by partially purified gp330, but not by purified gp108. Furthermore, binding of the eluted antibody to rat Fx1A was inhibited by both rat and human Fx1A. On immunoblot, the eluted antibody mainly reacted with a 440 kD glycoprotein of human Fx1A which showed the same mobility as rat gp330. The antibody also reacted with a band of gp330 of rat Fx1A. These results indicate that the 440 kD glycoprotein in humans is a counterpart of rat gp330 and that the eluted antibody has dual specificities to both human 440 kD glycoprotein and rat gp330, suggesting that the cross-reactive antibody is responsible for human Fx1A-induced HN.

Initial events in the formation of immune deposits in passive Heymann nephritis. gp330-anti-gp330 immune complexes form in epithelial coated pits and rapidly become attached to the glomerular basement membrane

The nephritogenic antigen of Heymann's nephritis (HN), gp330, was previously demonstrated (4-9) to be a resident glycoprotein of coated pits in the glomerular and proximal tubule epithelium of rats, and anti-gp330 IgG given intravenously was found to form IDs in glomeruli (passive HN). The purpose of this study was to investigate the detailed events that occur in the formation of IDs in passive HN. HN was induced by the injection of either 125I-labeled or unlabeled anti-gp330 IgG. At various times after injection (15 min to 8 d) the kidneys of some of the injected rats were fixed by perfusion, and the distribution of the rabbit IgG was determined by immunofluorescence and by immunoelectron microscopy. Glomeruli were isolated from the kidneys of injected rats and used for isolation of GBM fractions or for elution of the bound IgG. At 15 min to 1 h after injection, the rabbit IgG was localized by immunocytochemistry exclusively in coated pits along the podocyte plasmalemma facing the GBM. By 1-8 d, anti-gp330 IgG was detected in larger electron-dense IDs often located under the slit diaphragms. Serial sectioning revealed that each of the IDs maintained contact with a coated pit at some level. When GBMs isolated from rats given radiolabeled anti-gp330 IgG were examined by electron microscopy, the IDs were found to remain attached to the GBMs as early as 15 min after injection and coisolated with them at all time points. By double-immunolabeling of the isolated GBMs with two sizes of gold particles, both the antigen (gp330) and the anti-gp330 IgG could be demonstrated in IDs at all time points. When the amount of radiolabeled anti-gp330 bound to GBM fractions was compared with that of isolated glomeruli, it was found that 20% of the radiolabel remained bound to the purified GBMs at 15 min after injection, and 90% at 3 d. The bound IgG was released only by treatments that disrupt antibody-antigen complexes (high and low pH), but not by the other treatments we tried (detergent, high salt, heparinase, or collagenase digestion). When the IgG bound to glomeruli was eluted with acid citrate buffer 3 d after injection, it was found to specifically immunoprecipitate only gp330 from detergent-solubilized 125I-labeled kidney microvillar vesicles. By isoelectric focusing the eluate was found to be enriched in IgGs with acidic isoelectric points.(ABSTRACT TRUNCATED AT 400 WORDS)

An evaluation of the development of experimental membranous nephropathy

Heymann nephritis is a rat model of glomerulonephritis with morphologic manifestations of human membranous nephropathy. This model is generated by immunizing rats with Fx1A antigen. Passive Heymann's nephritis (PHN) can be produced by the administration of anti-Fx1A antibody (anti-Fx1A Ab) (with abnormal proteinuria appearing in 5 days). Studies were designed to examine the evolution of temporal changes in protein excretion, the glomerular ultrafiltration coefficient (LpA) and morphology of glomerular capillary three and five days after induction of PHN. Glomerular hemodynamic evaluation by micropuncture in euvolemic rats with PHN revealed normal values for nephron filtration rate (SNGFR), LpA and the glomerular hydrostatic pressure gradient (delta P) at day three, but by day five the whole kidney GFR and SNGFR were decreased, delta P increased and LpA significantly reduced. Glomerular binding of anti-Fx1A Ab increased from 38 micrograms/7.6 X 10(4) glomeruli on day three to 52 micrograms on day five. Immune complex deposits evaluated by immunofluorescence and electron microscopy appeared larger and were better defined on day five than on day three. Epithelial foot process fusion was more extensive on day five than day three. The onset of increased proteinuria correlated temporally with a reduction in LpA on day five, which in turn correlated with increased antibody binding, immune deposit accumulation and fusion of epithelial cell foot processes.

Glomerulonephritis induced in the rabbit by antiendothelial antibodies

The effects of interaction between endothelial angiotensin converting enzyme (ACE) and goat anti-rabbit ACE (GtARbACE) antibodies were studied in rabbit glomeruli. By immunofluorescence ACE was not detectable in normal glomeruli. However, when kidneys were perfused with GtARbACE antibodies glomerular bound IgG was seven times higher than that of non-immune IgG and granular deposits of goat IgG were found on the endothelium of glomeruli and arteries. Rabbits injected intravenous for 4 d with GtARbACE antibodies showed on day 1 granular deposits of goat IgG on the glomerular endothelium; from day 3 to 24 there was gradual development of subepithelial deposits of goat IgG, rabbit IgG and C3. When GtARbACE antibodies were similarly injected into proteinuric rabbits there was formation of subepithelial granular deposits of goat IgG and ACE. The results document that a glomerular endothelial antigen is redistributed in vivo by a specific ligand, an event associated with formation of immune deposits. Furthermore, if the glomerular permeability is artificially increased, immune complexes shed from nonglomerular endothelia into the circulation can contribute to form subepithelial immune deposits.

Indomethacin reduces proteinuria in passive Heymann nephritis in rats

Indomethacin has been used to lower proteinuria in human glomerular diseases with controversial results. The mechanism of indomethacin beneficial effects has not been established. A possible explanation is that indomethacin reduces proteinuria by inhibiting the synthesis of renal prostaglandins (PGs); however, appropriate studies to address this issue have never been done. The objectives of the present study were: to investigate whether indomethacin influences protein excretion in an experimental model of immunologically-mediated glomerular disease; to establish if the possible favorable effect of indomethacin on proteinuria is related to a reduction in glomerular filtration rate (GFR); to establish the possible association between the antiproteinuric effect of indomethacin and its inhibitory effect on arachidonic acid (AA) metabolites of renal or extrarenal origin; and to further investigate the relationship between proteinuria and renal thromboxane (Tx) synthesis previously demonstrated in experimental models of nephrotoxic nephritis and adriamycin (ADR) nephrosis. To this purpose we used an experimental immune-complex disease, passive Heymann nephritis (PHN) which was induced in the rat by a single intravenous (i.v.) injection of heterologous serum directed against a brush border component (gp 330 antigen). Indomethacin at a dose of 6 mg/kg intraperitoneally (i.p.) administered for four consecutive days to PHN animals during the period of heavy proteinuria, effectively reduced urinary protein excretion. The reduction in proteinuria does not appear to be a consequence of a reduction in GFR as documented by inulin clearance. Glomerular synthesis and urinary excretion of vasodilatory prostacyclin (PGI2) and PGE2 were decreased or unchanged in PHN animals in respect to control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Passive Heymann nephritis induced by rabbit antiserum to membrane antigens isolated from rat visceral yolk-sac microvilli

Passive Heymann nephritis (PHN) is an animal model of immune-complex-induced renal disease resembling human membranous glomerulonephritis. It was induced in rats by injecting rabbit antiserum directed against glycoprotein antigens isolated from rat embryonic visceral yolk-sac microvilli (VYS-MV). The glycoprotein antigens were isolated by extracting the VYS-MV with detergent Nonidet P-40 followed by gel filtration in Sephacryl S-300 and finally by lectin affinity chromatography with Ricinus communis agglutinin I. In vitro immunofluorescent localization studies demonstrated that the nephritogenic antibodies were localized along the apical region of the visceral yolk-sac endodermal cells and the brush border of the proximal tubular cells of the kidney. Rats injected with a single dose of the antiserum manifested proteinuria. Indirect immunofluorescent studies showed that the injected rabbit IgG was localized in vivo along the capillary walls of the glomerulus in a granular fashion. Electron microscopic examination of the same kidney glomeruli revealed numerous electron-dense deposits along the lamina rara externa of the glomerular basement membrane. Fusion of the epithelial foot processes was also present. These findings represent the typical immunopathological characteristics of Heymann nephritis. Furthermore, with the aid of Ouchterlony analysis, the antiserum against the isolated VYS antigens exhibited an immunoprecipitin band which was in common with that formed by the antiserum against the homogeneous nephritogenic antigen (gp330) of renal brush border origin. Thus, the nephritogenic antigens which have been found to be associated with the brush border of the renal proximal tubules may also be present or cross-reacted in the microvilli of the rat embryonic visceral yolk-sac.

Kidney immunopathology and pathophysiology in rats immunized with proximal tubule cell brush border or basolateral membrane vesicles

Proximal tubule pathology in Heymann nephritis has been attributed to anti-brush border antibodies, but antibodies with other specificities might also be important. To determine whether injury to the basolateral membranes of proximal tubules could occur independently of brush border injury, LEW rats were immunized either with partially purified basolateral or brush border membrane vesicles. Both immunogens produced glomerular immunopathology and pathophysiology identical in magnitude and time course to that seen in Heymann nephritis. Antibodies eluted from the kidneys of rats immunized with either antigen preparation stained the brush border in vitro. However, circulating anti-brush border antibodies were in significant titers only in rats immunized with brush border vesicles, whereas antibodies that stained the cytoplasm of both proximal and distal tubules predominated in rats immunized with basolateral membranes. With the onset of proteinuria, rats immunized with brush border membranes developed the proximal tubule pathology of Heymann nephritis. In rats immunized with basolateral membranes, the brush border and apical aspect of proximal tubule cells remained essentially normal. However, defects of basolateral membrane transport function were present, indicating that those defects need not necessarily be secondary to brush border damage. The dissociation of brush border damage from glomerular injury suggests that different antibody populations may account for each. Furthermore, anti-brush border antibodies may not account for all aspects of proximal tubule pathology in Heymann nephritis.

Lymphocyte expression of a 90 kD brush border antigen

This study analyses the expression by rat lymphocytes of six renal brush border (BB) antigens defined by a set of monoclonal antibodies and demonstrates that a 90 kD protein (gp 90), synthesized by BB and glomeruli is found on the surface of T and B cells. The other antigens, including the 330 kD protein involved in Heymann's nephritis--a model of epimembranous glomerulonephritis--are not detectable on the surface of lymphocytes. Immunochemical studies indicate that gp 90 and the related protein immunoprecipitated from thymocyte membranes co-migrate in SDS-PAGE. Quantitative binding analysis shows that the number of antigenic sites is in the same order of magnitude on thymocytes, spleen and bone-marrow lymphocytes as well as on two lines of pre-B and pre-T cells, but considerably lower on a highly differentiated helper T cell line.