Passive transfer of Heymann nephritis with serum

Publications With Nephrological Themes Appearing Diachronically in the PubMed Bibliographical Database

OBJECTIVES

Nephrology in the last 50 years has undergone important scientific developments, which have formally revolutionized clinical practice, including renal biopsy, renal replacement therapy, and transplantation. The understanding of the pathogenesis and the clinical course of renal disease has also steadily improved, resulting in renewal of definitions, classifications, and therapeutics in nephrology. In this context, publications with nephrological content are also expanding. The aim of this bibliographic study was to analyze publications related to nephrology-specific key words in the PubMed database.

MATERIALS AND METHODS

We included the key words "nephrology," "acute renal failure," "renal biopsy," "hemodialysis," "peritoneal dialysis," and "renal transplantation" as search terms in PubMed in May 2022. We also used the term "kidney" as an alternative to "renal."

RESULTS

"Nephrology" appeared 185 545 times in searches, with its appearance expanding in the past 3 decades since 1948. The term "acute renal failure" was found in 1932 in 1 publication and in a total number of 92 278 publications. Renal biopsy appeared since 1943 in 18 048 publications. "Hemodialysis" appeared in 182 730 citations, with the first in 1915. "Peritoneal dialysis" appeared in 32 266 citations for the first time in 1901 and in 1946 in human application. One publication on "renal transplantation" appeared in 1946, with 106 075 total publications related to renal transplantation.

CONCLUSIONS

We viewed a clear expansion of nephro-logical publications in the past decades. Hemodialysis remains the most frequently used term in nephrology-related publications. Historical analysis of the PubMed database is useful as a tool to understand the research and publication trends in nephrology, as we approach the new era of precision medicine.

Sanqi Oral Solution Mitigates Proteinuria in Rat Passive Heymann Nephritis and Blocks Podocyte Apoptosis via Nrf2/HO-1 Pathway

Idiopathic membranous nephropathy (IMN) is the most common pathological type in adult nephrotic syndrome where podocyte apoptosis was found to mediate the development of proteinuria. Sanqi oral solution (SQ), an effective Chinese herbal preparation clinically used in treatment of IMN for decades, plays an important role in reducing proteinuria, but the underlying mechanisms have not been fully elucidated yet. The current study tested the hypothesis that SQ directly lessens proteinuria in IMN by reducing podocyte apoptosis. To investigate the effects of SQ, we established the experimental passive Heymann nephritis (PHN) rat model induced by anti-Fx1A antiserum in vivo and doxorubicin hydrochloride (ADR)-injured apoptotic podocyte model in vitro. SQ intervention dramatically reduced the level of proteinuria, together with the rat anti-rabbit IgG antibodies, complement C3, and C5b-9 deposition in glomerulus of PHN rats, accompanied by an elevation of serum albumin. Protein expression of synaptopodin, marker of podocyte injury, restored after SQ administration, whereas the electron microscopic analysis indicated that fusion of foot processes, and the pachynsis of glomerular basement membrane was markedly diminished. Further studies showed that SQ treatment could significantly inhibit podocyte apoptosis in PHN rats and ADR-injured podocytes, and protein levels of Cleaved Caspase-3 or the ratio of Bax/Bcl-2 were significantly decreased with SQ treatment in vivo or in vitro. Moreover, we found that the nuclear factor erythroid 2–related factor-2/heme oxygenase 1 (Nrf2/HO-1) pathway mediated the anti-apoptosis effective of SQ in podocyte. Thus, SQ mitigates podocyte apoptosis and proteinuria in PHN rats via the Nrf2/HO-1 pathway.

A conceptual framework linking immunology, pathology, and clinical features in primary membranous nephropathy

Primary membranous nephropathy is a leading cause of adult nephrotic syndrome. The field took a major step forward with the identification of phospholipase A2 receptor (PLA2R) as a target antigen in the majority of cases and with the ability to measure circulating autoantibodies to PLA2R. Since then, the existence of additional target antigens such as thrombospondin type-1 domain-containing 7A, exostosin 1 and 2, neural EGFL like 1, and semaphorin 3B has been demonstrated. The ability to detect and monitor levels of circulating autoantibodies has opened a new window onto the humoral aspect of primary membranous nephropathy. Clinicians now rely on clinical parameters such as proteinuria, as well as levels of circulating autoantibodies against PLA2R and the results of immunofluorescence staining for PLA2R within kidney biopsy tissue, to guide the management of this disease. The relationship between immunologic and clinical disease course is consistent, but not necessarily intuitive. In addition, kidney biopsy provides only a single snapshot of disease that needs to be interpreted in light of changing clinical and serological findings. A clear understanding of these dynamic parameters is essential for staging, treatment, and management of this disease. This review aims to shed light on current knowledge regarding the development and time course of changes in the serum levels of autoantibodies against PLA2R, proteinuria, and histological findings that underlie the pathophysiology of primary membranous nephropathy.

Autoantibodies in the Diagnosis, Monitoring, and Treatment of Membranous Nephropathy

The discovery of anti-podocyte antibodies in primary membranous nephropathy (MN) has revolutionized our approach toward the diagnosis and treatment of this disease. Evaluation of serum levels of anti-podocyte antibodies paved the way for non-invasive diagnosis and helped distinguish between primary and secondary MN although the relationship between anti-podocyte antibodies and cancer remains to be elucidated. Serum levels of anti-PLA2R antibodies directed against the major podocyte autoantigen are related to MN activity and the decrease in serum levels of anti-PLA2R antibodies in response to treatment (immunologic remission) also serves as an early indicator of the later putative proteinuric remission, enabling personalization of the treatment. The serum levels of anti-podocyte antibodies also enable the prediction of renal outcomes in terms of both remission and the risk of progression to end-stage renal disease. The positivity of anti-PLA2R antibodies before renal transplantation is associated with the risk of recurrence of MN. It remains to be established if all these relations observed in patients with anti-PLA2R antibodies are also valid for expanding spectrum of antibodies directed against recently discovered minor antigens (e.g., THSD7A, NELL-1, semaphorin 3B).

Immunopathological events initiated and maintained by pathogenic IgG autoantibodies in an experimental autoimmune kidney disease

The experimental models of Heymann nephritis (HN) and slowly progressive Heymann nephritis (SPHN) give us rare opportunities to investigate the etiologies and pathogenesis of two immunopathological processes in rats leading to: (1) autoimmune disease, where the autoimmune disease HN and SPHN is initiated and maintained by cross-reactive pathogenic IgG autoantibodies (aabs) directed against the renal proximal convoluted tubules' brush border (BB) cells - where the nephritogenic antigen (ag) is produced and localized - damaging and releasing BB associated nephritogenic ag into the circulation which in turn contributes to continuation of the autoimmune disease; and (2) immune complex glomerulonephritis, where the glomerular injury is initiated, proceeding into a chronic progressive disease by depositing immune complexes (ICs) - made up of a glomerular epithelial cell produced endogenous nephritogenic ag and the developing pathogenic IgG aab directed against the nephritogenic ag, and complement components - on the epithelial side of the glomerular basement membrane. We also observed how the normally functioning immune system is able to avert autoimmune disease developments by circulating specific non-pathogenic IgM aabs clearing the system of intracytoplasmic ags released from cells at the end of their life spans or following damage by toxic agents. We also described how an autoimmune disease SPHN can be prevented and when present terminated by the implementation of a new vaccination technique we have developed and call modified vaccination technique. By increasing the specific IgM aab production against the native nephritogenic ag - by injecting ICs made up of: [nephritogenic ag X homologous anti-nephritogenic ag IgM ab] in slight ag excess into SPHN rats - pathogenic IgG aab producing native and modified nephritogenic ags were removed from the circulation and termination of the autoimmune disease causing immune events was achieved. Even though HN and SPHN are not well-known disease models, their studies are important because the etiologies and pathogenesis of two conditions - that can also occur in humans, namely autoimmune diseases and membranous glomerulonephritis - can be simultaneously investigated.

Nephrin and podocin dissociate at the onset of proteinuria in experimental membranous nephropathy

BACKGROUND

The slit diaphragm plays a critical role in maintaining the barrier function of the glomerular capillary wall. The pathogenic mechanism of proteinuria in membranous nephropathy remains uncertain. This study was undertaken to analyze the pathogenic role of slit diaphragm in proteinuria in experimental membranous nephropathy.

METHODS

The expression and the localization of slit diaphragm-associated molecules (nephrin, podocin, and CD2AP) and other podocyte-associated molecules (podocalyxin and alpha(3) integrin) in passive and active Heymann nephritis were analyzed by immunofluorescence and Western blot analysis. The interaction of slit diaphragm-associated molecules was investigated by the dual-labeling immunofluorescence method. The mRNA expression of these molecules was also analyzed.

RESULTS

Shifts in nephrin and podocin staining patterns, from linear to granular, were detected in the early stages of passive Heymann nephritis. These shifts were not parallel, and the dissociation of these molecules was detected by the dual-labeling immunofluorescence method in passive and active Heymann nephritis. Western blot analyses with sequentially solubilized materials indicated that the nephrin-rich fraction changed from being partly detergent-resistant to being predominantly detergent-soluble. This change did not occur with podocin. Nephrin excreted into urine was already detected in the early stages of passive Heymann nephritis. Decreased mRNA expression of nephrin and podocin was observed before the onset of proteinuria. By contrast, no extensive change in the expression of alpha(3) integrin was observed in this study.

CONCLUSION

Nephrin is dissociated from podocin and excreted into urine in the early stages of Heymann nephritis. The reduced expression of nephrin and podocin, along with their dissociation, may contribute to the development of proteinuria in Heymann nephritis.

Membranous glomerulonephritis induced in the pig by antibody to angiotensin-converting enzyme: considerations on its relevance to the pathogenesis of human idiopathic membranous glomerulonephritis

In the course of studies on the humoral consequences of swine to primate xenotransplantation, the investigators induced formation of glomerular subepithelial immune deposits and tubular lesions in pigs injected with heterologous antibody to angiotensin-converting enzyme. This study describes the morphology of the lesions, discusses their mechanism, explains their relevance for understanding the pathogenesis of human idiopathic membranous glomerulonephritis, and proposes future directions for investigations.

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

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

Autoimmunity and the pathogenesis of glomerulonephritis

Self-tolerance is maintained by: thymic influences on developing T cells; peripheral mechanisms that can tolerise post-thymic T cells; and to a variable extent the tolerisation of potentially autoreactive B cells. The presence of autoreactive T cells in normal individuals suggests that mechanisms to control the activity of such cells may be important. Failure of any of these processes may lead to autoimmunity. The relationship between glomerulonephritis and the mechanisms leading to breakdown of self-tolerance remains elusive. An important observation is that autoimmune diseases are strongly associated with particular products of the major histocompatibility complex (MHC). This association may reflect the intimate involvement of the MHC in thymic T cell education. Another explanation is that T cells only recognise antigens presented in the context of MHC molecules. Although there has been progress in identifying the targets recognised by autoantibodies in vasculitis and anti-GBM disease, nothing is known about the T cells involved. Despite our ignorance, therapy aimed specifically at the T cell can be effective. This approach is being supplemented by attempts to engage immunoregulatory mechanisms, such as idiotype-antiidiotype interactions. The hope is that such treatments, or combinations thereof, will allow a more focused suppression of the autoimmune response, in contrast to the non-specific (and therefore potentially dangerous) methods of immunosuppression available at present.

Non-systemic glomerulonephritis: exposure to nephro- and immunotoxic chemicals predispose to immunologic harassment

Glomerulonephritis is thought to be caused by immune complexes trapped or formed in the glomeruli. But immune complexes are found in the glomeruli of many normal mammals and of patients with non-renal diseases, and immune complexes trapped or formed experimentally in the glomeruli induce mild proteinuria at most suggesting that additional factors must be responsible. An induction of serious renal damage in experimental glomerulonephritis demands a chronic supply of antigen, rarely seen in human glomerulonephritis; or the use of heterologous antibodies, a design with questionable clinical relevance; or immuno- and nephrotoxic chemicals; or Freund's adjuvant which is also nephrotoxic. It is therefore suggested that the pathogenesis of human non- systemic glomerulonephritis includes exposure to nephro- and immunotoxic chemicals, the deposition of glomerular immune complexes being secondary. The hypothesis has clinical support: a majority of patients have been exposed to such chemicals, mainly hydrocarbons; and the tubulointerstitial changes in glomerulonephritis are better correlated to renal function and clinical course than are the glomerular changes. The chemicals enhance or derange immunizations and sensitize the kidneys to immunological reactions.

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.

The organ distribution of gp-330 (Heymann antigen) and gp-90 in the mouse and the rat

The Heymann antigen (gp-330) and an antigen with lower molecular weight (gp-90) are major constituents of the brush border of the renal proximal tubules in the rat and the mouse. The Heymann antigen can also be found at discrete sites in the glomerular visceral epithelium of the rat, but not of the mouse. Gp-90 is present diffusely along the glomerular capillary wall of rat and mouse. The Heymann antigen is probably the target antigen for membranous glomerulonephritis in the rat, while in the mouse, where this form of glomerulonephritis can also be induced, gp-90 seems to be the antigen involved. We have separated the antibody populations against these two antigens by preparing eluates from kidneys of rats and livers of mice that had been injected with an antiserum against pronase-digested mouse renal tubular antigens. Using these purified antibodies we have examined by indirect immunofluorescence the distribution of the two antigens on normal mouse and rat tissues. The expression of the Heymann antigen is limited to the epithelia of several organs, while gp-90 has a more widespread distribution in many cells of different origin and function in both the mouse and the rat.

Influence of renal transplantation in rats on glomerular and tubular immune complexes

Kidneys were transplanted from rats with immune complex nephritis to normal rats to determine the role of circulating antibodies to renal antigens in the maintenance of immune complexes. Glomerular subepithelial immune complexes in nine proteinuric donor rats, actively or passively immunized with proximal tubular antigen Fx1A (active and passive Heymann nephritis), were studied at the time of transplantation and two to four and one-half months after transplantation to normal unilaterally nephrectomized recipient rats. These subepithelial IgG deposits and proteinuria persisted throughout the four-month period after transplantation. Tubular subepithelial immune complexes in the kidneys of nine rats, actively immunized with a distal renal tubular antigen, Tamm-Horsfall protein, were studied at the time of transplantation when donors had high circulating IgG antibody titers to Tamm-Horsfall protein and at one to eight weeks after transplantation. The abundant granular and nodular immune complexes of rat IgG and Tamm-Horsfall protein at the base of tubular cells were very rapidly cleared during the first two weeks after transplantation and were virtually absent by four weeks. The rapid clearance of tubular immune complexes after transplantation of kidneys from actively immunized rats followed a time course similar to that after passive immunization with antisera to Tamm-Horsfall protein. These findings support the concept that high titers of circulating antibodies to Tamm-Horsfall protein are required to prevent the rapid clearance of tubular immune complexes, a process that is facilitated by conditions of antigen excess at the surface of tubular cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The autoimmune response in active Heymann's nephritis in Lewis rats is regulated by T-lymphocyte subsets

In this study the cellular events which are responsible for the induction and suppression of active Heymann's nephritis (HN) in Lewis rats were investigated. Using an enzyme-linked short-term culture assay specific autoantibody production in vitro by lymphoid cells directed against the nephritogenic renal tubular epithelial glycoprotein (RTE-Gp) was measured. By this method it was shown that only the lymph nodes that drain the site of immunization contained autoreactive B cells. Pretreatment with cyclosporine A (Cy-A) or with multiple injections of high doses of antigen in Freund's incomplete adjuvant markedly inhibited the development of disease to a subsequent nephritogenic challenge. In challenged high-dose-tolerant (HDT) rats the autoimmune response was only 5-10% of immunized nontolerant rats. This tolerance could not be transferred by lymphoid cells from Cy-A-treated rats, but could be transferred by lymphoid cells derived from the thymus or spleen of HDT rats. Thus a suppressor cell of thymic origin may be responsible for HDT. Transfer of affinity column-fractionated splenic T cells from HDT rats demonstrated that OX8- helper and OX8+ suppressor T cells are involved in the induction and suppression, respectively, of the autoimmune response in this experimental nephropathy.

In vivo interaction of antibodies with cell surface antigens. A mechanism responsible for in situ formation of immune deposits in the zona pellucida of rabbit oocytes

It was the aim of this study to test the hypothesis that the interaction of antibodies with antigens expressed on the plasma membrane of cells surrounded by a basement membrane or a basement membrane-like structure results in in situ formation of immune deposits. Ovary was chosen for the experiments because we found that a well-characterized protein, angiotensin-converting enzyme (ACE), is expressed in a diffuse pattern on the plasma membrane of mature oocytes. To investigate the events following the in vivo interaction of oolemma-ACE with its antibody, rabbits were injected with goat anti-rabbit ACE gamma-globulin or with Fab fragments of goat anti-rabbit ACE IgG in an ear vein for a maximum of 4 d; they were followed for up to 20 d thereafter. Ovary tissue was studied by immunofluorescence, and immunoelectron, light, and transmission electron microscopy. The results of this study document two new findings: First, that ACE is expressed on the oolemma of rabbit oocytes. Second, that the in vivo interaction of divalent antibodies to this cell surface antigen induces formation of granular immune deposits in the adjacent zona pellucida through a mechanism of "patching" and "shedding" of immune complexes, similar to that occurring in in vitro systems characterized by interaction of plasma membrane receptors with soluble ligands. This mechanism might have importance in the pathogenesis of Heymann glomerulonephritis and of other immunological diseases involving antigens expressed on the plasma membrane of cells.

Spontaneous glomerulonephritis in rabbits: role of a glomerular capillary antigen

Overt glomerulonephritis, detected by abnormal proteinuria, occurred in 3.3% of young (2.5 kg) male New Zealand White (NZW) rabbits. Histologically, mild to moderate mixed membranous and proliferative glomerulonephritis was observed. Glomerular deposits of IgG and C3 and electron microscopic findings were not typical of circulating immune complex accumulation, nor did they suggest anti-glomerular basement membrane (GBM) antibody. Segmental and less intense glomerular deposits of IgG were found in up to 48% of nonproteinuric NZW rabbits of the same age; histologic changes were minimal. IgG antibodies in sera from proteinuric rabbits or eluted from their kidneys reacted by indirect immunofluorescence with antigens distributed (discontinuously) along the glomerular capillary walls, and in some cases within the walls of small arteries of normal rabbit kidney sections. By indirect immunoperoxidase electron microscopy, the reactive antigens were present at the surfaces of the epithelial cell foot processes where they abut the GBM. This spontaneous glomerulonephritis appears to involve fixation of antibodies to antigens distributed in a discontinuous pattern in the glomerular capillary wall. The mechanism would be much like that causing anti-GBM antibody glomerulonephritis, except that the glomerular antigen is different. Possibly some forms of glomerulonephritis develop in humans as a result of a similar process.

Restoration of antigenicity of tissue antigens, cell-bound immunoglobulins and immune deposits in paraffin-embedded tissue. The influence of fixation and proteolytic enzymatic digestion

The possibility of preservation and restoration of antigenicity of some antigens in paraffin-embedded tissue was evaluated by direct immunofluorescent technique on deparaffinized sections. Fixation with 96% ethanol-1% acetic acid, 10% neutral buffered formalin and p-formaldehyde was useful for the preservation of tissue antigens and immune deposits, whose antigenicity could be easily restored by trypsin digestion. Neutral buffered formalin was also a satisfactory fixative in immunofluorescent staining on lymphocyte/plasma cell-bound immunoglobulins. Fixation with alcohol-Bouin's fluid showed contrast results; feasible for staining of cell-bound immunoglobulins, but poor for that of glomerular immune deposits. After papain digestion, BSA and lysozyme, antigens of immune complexes, were easily detected in experimental chronic serum sickness glomerulonephritis. Pepsin was more efficient than trypsin in restoring the antigenicity of renal tissue antigens such as fibronectin and polyantigenic basement membrane, but the brush border antigen of the proximal renal tubules was frail to the pepsin digestion. In general, the enzymatic digestion time necessary for the restoration of antigenicity was in parallel with fixation time. Results obtained have shown that deparaffinized sections could be used as satisfactory substrate for immunohistochemistry when proper fixation and efficient proteolytic enzymatic pretreatments were performed.

Immunocytochemical localization of the Heymann nephritis antigen (GP330) in glomerular epithelial cells of normal Lewis rats

The nephritogenic antigen of Heymann's nephritis (HN) was previously purified from tubular brush-border fractions of rat kidney and found to be a 330,000- mol-wt glycoprotein (gp330). This study was conducted to determine whether gp330 is also present in the rat glomerulus, and, if so, to establish where in the glomerulus it is located. Rabbit polyclonal and mouse monoclonal antibodies were raised against purified gp330, which specifically immunoprecipitated gp330 from solubilized brush-border fractions and specifically stained microvilli and coated invaginations (located at the base of the microvilli) of proximal tubule cells. Accordingly, they were used to localize gp330 by immunoprecipitation and immunocytochemistry in glomeruli of normal Lewis rats. For immunoprecipitation, purified glomerular fractions were prepared from [(35)S]-methionine-labeled kidneys, extracted with Triton X-100, and the extract was used for immunoprecipitation with affinity-purified rabbit polyclonal, or mouse monoclonal, anti-gp330 IgG. Analysis of immunoprecipitates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorography indicated that a band corresponding in mobility to gp330 was specifically precipitated. When unfixed cryostat sections were incubated for indirect immunofluorescence with monoclonal or affinity-purified polyclonal IgG, a fine granular fluorescent staining was seen throughout the glomerulus. When aldehyde-fixed cryostat sections were incubated for indirect immunoperoxidase, reaction product was detected only in the epithelial cells and was not seen in the GBM, endothelium, or mesangium. Within the epithelium it was localized to the endoplasmic reticulum, occasional Golgi elements, multivesicular bodies, and coated pits at the cell surface. The reactive coated pits were distributed all along the cell membrane, including the sides and base of the foot processes. Reaction product was detected in the latter location only in sections that had been digested with neuraminidase before antibody incubation. When rats were given rabbit anti-gp330 IgG by intravenous injection and their kidneys stained for direct immunoperoxidase 3 d later, rabbit IgG was seen to be deposited beneath the slit diaphragms and in the coated pits at the base of the foot processes. The immunocytochemical and immunoprecipitation data indicate, in confirmation of the results of others, that the nephritogenic HN antigen is present in renal glomeruli as well as in proximal tubular brush borders. The immunocytochemical results further demonstrate that gp330 is an epithelial, rather than a glomerular basement membrane, antigen. It appears to be synthesized by glomerular epithelial cells and subsequently becomes concentrated in coated pits. As both the endogenous antigen (gp330) and exogenously administered anti-gp330 antibody were localized to coated pits, it seems likely that coated pits located at the base of the foot processes are the sites where the HN antigen (gp330) and circulating antibodies directed against gp330 meet and where immune complexes are formed.

Alteration of glomerular anionic sites by the development of subepithelial deposits in experimental glomerulonephritis in the rat

Using highly cationic polyethleneimine, alteration of glomerular anionic sites were evaluated ultrastructurally in two types of rat glomerulonephritis (GN); chronic serum sickness GN and heterologous (passive) or autologous (active) Heymann's GN. Daily i.v. injections of egg white lysozyme in physiologic saline into presensitized rats led to the formation of numerous mesangial and subepithelial deposits. In the non-proteinuric period in which immune deposits were localized predominantly in the mesangium, anionic sites of the laminae rarae and the epithelial cell coat were clearly observed. In the subsequent proteinuric period in which numerous subepithelial deposits were superimposed, a broad loss of anionic sites in the epithelial cell coat was seen. Splitting and focal loss of anionic sites on the lamina rara externa adjacent to the subepithelial deposits were commonly observed both in passive and active Heymann's GN and in lysozyme GN. These findings indicate that the subepithelial deposits are closely involved in the development of proteinuria by injuring the anionic sites, especially those on lamina rare externa of the glomerular basement membrane.

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

Purified brush border fractions prepared from rat kidneys were solubilized in detergent, iodinated, and subjected to immunoprecipitation to identify the pathogenic antigen present in brush border membranes that is responsible for the production of Heymann nephritis (HN). Purified IgG prepared from the sera of rabbits or rats immunized with a crude cortical preparation, known as Fx1A, precipitated multiple peptides, whereas IgG eluted from glomeruli of rats with active or passive HN specifically immunoprecipitated a single large glycoprotein (Mr = 330,000). This protein (gp330) was subsequently purified by gel filtration and lentil lectin affinity chromatography from detergent-solubilized brush border membranes. When rats were immunized with purified gp330, they developed anti-brush border antibodies and active HN. IgG prepared from the serum of rats with active HN caused passive HN when injected into normal recipients. Rats immunized against brush border membrane proteins depleted of gp330 developed anti-brush border antibodies but did not develop HN. Further analysis of gp330 indicated that it is solubilized by detergent treatment of isolated brush border microvilli, and its antigenic component is released from intact microvilli by trypsin. By immunoperoxidase staining it was localized to the luminal side of the brush border membranes. These results indicate that (i) gp330 is the pathogenic antigen of HN; (ii) the antigen is a glycoprotein of the brush border membrane; and (iii) it is disposed with its pathogenic domain(s) facing the tubule lumen.

Glomerular antigens in glomerulonephritis

Ideas on the immunopathogenesis of glomerulonephritis are evolving to embrace a concept of a dynamic and constantly fluctuating involvement of immune reactants in the production of glomerular inflammation. The glomerulus should be regarded as a template around which the antibody-induced inflammatory events that constitute glomerulonephritis are initiated. Such lesions may be produced by direct antibody attack on glomerular antigens of either intrinsic structural or "planted" type, as discussed in this review, or by the deposition of circulating soluble immune complexes containing extraglomerular antigens. These mechanisms are not mutually exclusive and both may play a role in some situations. Intrinsic glomerular antigens are being increasingly better defined as to site, structure, function, and experimental animal models of spontaneous and induced glomerular injury resulting from direct antibody binding to nonclassic GBM capillary wall antigens are available for study. Similar nonclassic GBM antigens are likely to be found of importance in man. Anti-GBM antibody-induced glomerulonephritis continues to be the best understood example of direct attack on the glomerulus by antibody, and its nephritogenic noncollagenous GBM antigenic constituents are being characterized. The incorporation of extraneous substances as "planted" antigens within glomerular structures is now recognized in experimental animal models, and there is suggestive evidence to support the concept in man. Emphasis needs to be placed on the continuing interplay of free antibody and antigen with deposited reactants which, together with complement components, modulate the quality and quantity of the glomerular immune deposits.

Antibody-mediated injury to proximal tubules in Heymann nephritis

To evaluate the hypothesis that antibody-mediated damage to proximal tubules (PT) could be a feature of Heymann nephritis (HN), we studied the kidneys of rats in different stages of the disease by light, immunoflourescence (IF), transmission, and scanning electron microscopy. The observations of morphology were correlated with titers of circulating antibodies directed against the brush border (BB) and with proteinuria. Antibody titers reached a maximum 5 to 7 weeks after immunization with Fx1A, coincident with the onset of proteinuria. IgG and C3 were deposited along the BB of PT in all animals within the first week of proteinuria. BB antibodies were present in the urine of those rats. As antibody titers declined, a decrease in the extent of in vivo IgG deposition along the BB was also noted. The results of indirect IF tests, by using BB antibodies on kidneys of rats with HN of 3 to 4 months' duration, suggested extensive loss of the BB antigen(s) from the PT. Numerous granular deposits of IgG were present along the basement membrane of PT at that time. Study of kidney histology revealed that deposition of IgG and C3 along the BB of PT was associated with extensive loss of microvilli, as well as degeneration and proliferation of PT cells. Subepithelial electron-dense deposits were present along the basement membrane of PT. In rats with HN of more than 4 months' duration, with little or no circulating BB antibodies and persistent proteinuria, IgG and C3 were found in minimal amounts along BB. Examination by light and electron microscopy provided evidence of partial recovery of PT lesions in those kidneys. Rats with similar proteinuria resulting from chronic serum sickness did not have similar abnormalities of PT. These observations are consistent with the interpretation that, in rats with HN, BB antibodies induce cytotoxic injury to PT.

The pathogenesis of experimental membranous glomerulonephritis induced with homologous nephritogenic tubular antigen

The renal tubular epithelial antigen (Tub-Ag) of rats was solublized by Pronase and purified by gel filtration and acrylamide gel electrophoresis. Purified Tub-Ag was a glycoprotein with S20,W value of 8.4. Utilizing radiolabeled Tug-Ag, a sensitive radioimmunoassay for Tub-Ag and homologous antibody (anti-Tub-Ag) was developed. Tub-Ag activity associated with a protein of the same molecular size was demonstrated in the serum, as well as in Pronase extracts of all the organs tested, including kidney, liver, lung, spleen, intestine, stomach, and heart. The physiochemical properties of the Tub-Ag of rats and its distribution were essentially the same as the Tub-Ag of humans, which had been found in immune deposits in the kidney of some patients with idiopathic membranous glomerulonephritis. Rats were immunized with the purified Tub-Ag emulsified in Freund's complete adjuvant and followed for Tub-Ag and anti-Tub-Ag in the serum, as well as for proteinuria and immunohistological changes in the kidney. Serum Tub-Ag dropped sharply after 20 days, when anti-Tub-Ag appeared in the circulation. Persistent, massive proteinuria appeared still later, more than 30 days after injection, when anti-Tub-Ag disappeared and Tub-Ag reappeared in the serum of some of those rats. In others, anti-Tub-Ag in the serum persisted throughout the observation period of 90 days. The pathology of the kidney of the rats with proteinuria was that of a typical membranous glomerulonephritis; thickening of glomerular capillary walls with granular deposits of gamma-globulin and Tub-Ag was observed. On the basis of these results, Tub-Ag in the serum, probably released from cellular membranes of various organs as a physiological metabolite, is considered to maintain the pathological process in the kidney by providing the antigen continuously to form immune complexes.

Altered functional properties of the renal glomerulus in autologous immune complex nephritis: an ultrastructural tracer study

The altered functional properties of the glomerular capillary wall in a model of autologous immune complex disease (Heymann's nephritis) was studied by electron microscopy using intravenously injected protein tracers of varying molecular weight. There was an increase in the permeability of the glomerular basement membrane (GBM) itself to large molecules; this change was focal and was found in those areas where the GBM contained immune complex deposits. Both ferritin and catalase, tracers normally restricted from passing the glomerular filter, were present in the urinary space within minutes of injection. No evidence was obtained for increased glomerular epithelial transport in this disease. Foot process swelling and "close" junction formation was moderate, even in animals with marked degrees of proteinuria. Indirect evidence, therefore, makes an alteration in the slit pore complex likely. In addition, there was immediate and selective concentration of all tracers within deposits, though ferritin was partially excluded from some deposits. This phenomenon may be of significance in the perpetuation of the disease.