Glomerulonephritis induced in the rabbit by antiendothelial antibodies

Evaluation of urine dipstick for proteinuria assessment in pet rabbits

BACKGROUND

Naturally occurring kidney disease (KD) in pet rabbits has not been fully characterized. It has been previously suggested that proteinuria, especially when associated with isosthenuria, may be an early indicator of KD prior to azotaemia in rabbits. The aim of the current study was to assess the diagnostic utility of the urinary protein dipstick test (UPDT) for detecting proteinuria in rabbit urine samples as a useful diagnostic tool in clinical setting.

METHODS

Three hundred urinalyses from 156 pet rabbits were retrospectively analysed by comparing the UPDT with the urine protein:creatinine ratio (UPC) to assess its diagnostic performance in detecting proteinuria, defined as UPC > 0.3. Sensitivity, specificity, positive and negative predictive values (NPVs) were determined.

RESULTS

When urine-specific gravity (USG) was ≤1.024 and a UPDT result of >0 was considered proteinuric, the specificity and positive predictive value (PPV) were both 100%. Following the same criteria, specificity and PPV decreased to 92.1% and 92.5% when USG was ≤1.038. NPVs were poor.

CONCLUSION

In rabbits, a UPDT result > 0 is indicative of proteinuria (UPC > 0.3) when the USG is ≤1.024. In all other cases, proteinuria should be measured using the UPC.

Increased HDL Size and Enhanced Apo A-I Catabolic Rates Are Associated With Doxorubicin-Induced Proteinuria in New Zealand White Rabbits

The catabolism and structure of high-density lipoproteins (HDL) may be the determining factor of their atheroprotective properties. To better understand the role of the kidney in HDL catabolism, here we characterized HDL subclasses and the catabolic rates of apo A-I in a rabbit model of proteinuria. Proteinuria was induced by intravenous administration of doxorubicin in New Zealand white rabbits (n = 10). HDL size and HDL subclass lipids were assessed by electrophoresis of the isolated lipoproteins. The catabolic rate of HDL-apo A-I was evaluated by exogenous radiolabelling with iodine-131. Doxorubicin induced significant proteinuria after 4 weeks (4.47 ± 0.55 vs. 0.30 ± 0.02 g/L of protein in urine, P < 0.001) associated with increased uremia, creatininemia, and cardiotoxicity. Large HDL2b augmented significantly during proteinuria, whereas small HDL3b and HDL3c decreased compared to basal conditions. HDL2b, HDL2a, and HDL3a subclasses were enriched with triacylglycerols in proteinuric animals as determined by the triacylglycerol-to-phospholipid ratio; the cholesterol content in HDL subclasses remained unchanged. The fractional catabolic rate (FCR) of [(131)I]-apo A-I in the proteinuric rabbits was faster (FCR = 0.036 h(-1)) compared to control rabbits group (FCR = 0.026 h(-1), P < 0.05). Apo E increased and apo A-I decreased in HDL, whereas PON-1 activity increased in proteinuric rabbits. Proteinuria was associated with an increased number of large HDL2b particles and a decreased number of small HDL3b and 3c. Proteinuria was also connected to an alteration in HDL subclass lipids, apolipoprotein content of HDL, high paraoxonase-1 activity, and a rise in the fractional catabolic rate of the [(131)I]-apo A-I.

Autoantibodies and resident renal cells in the pathogenesis of lupus nephritis: getting to know the unknown

Systemic lupus erythematosus is characterized by a breakdown of self-tolerance and production of autoantibodies. Kidney involvement (i.e., lupus nephritis) is both common and severe and can result in permanent damage within the glomerular, vascular, and tubulo-interstitial compartments of the kidney, leading to acute or chronic renal failure. Accumulating evidence shows that anti-dsDNA antibodies play a critical role in the pathogenesis of lupus nephritis through their binding to cell surface proteins of resident kidney cells, thereby triggering the downstream activation of signaling pathways and the release of mediators of inflammation and fibrosis. This paper describes the mechanisms through which autoantibodies interact with resident renal cells and how this interaction plays a part in disease pathogenesis that ultimately leads to structural and functional alterations in lupus nephritis.

Experimental Models of Membranous Nephropathy

Membranous nephropathy (MN) is one of the commonest glomerular diseases, typically presenting in older males with nephrotic syndrome. The development and characterization of animal models of MN, in particular, the passive Heymann nephritis model (PHN), has greatly advanced our understanding of this disease. In this review we discuss the different animal models of human MN that are available, with an emphasis on the PHN model, including technical issues, the typical disease course and its application to human disease.

Evidence for a novel human-specific xeno-auto-antibody response against vascular endothelium

Humans are genetically unable to synthesize the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc). However, Neu5Gc can be metabolically incorporated and covalently expressed on cultured human cell surfaces. Meanwhile, humans express varying and sometimes high titers of polyclonal anti-Neu5Gc antibodies. Here, a survey of human tissues by immunohistochemistry with both a monospecific chicken anti-Neu5Gc antibody and with affinity-purified human anti-Neu5Gc antibodies demonstrates endothelial expression of Neu5Gc, likely originating from Neu5Gc-rich foods like red meats. We hypothesized that the combination of Neu5Gc incorporation and anti-Neu5Gc antibodies can induce endothelial activation. Indeed, the incubation of high-titer human sera with Neu5Gc-fed endothelial cells led to Neu5Gc-dependent antibody binding, complement deposition, endothelial activation, selectin expression, increased cytokine secretion, and monocyte binding. The proinflammatory cytokine tumor necrosis factor-alpha also selectively enhanced human anti-Neu5Gc antibody reactivity. Anti-Neu5Gc antibodies affinity-purified from human serum also directed Neu5Gc-dependent complement deposition onto cultured endothelial cells. These data indicate a novel human-specific mechanism in which Neu5Gc-rich foods deliver immunogenic Neu5Gc to the endothelium, giving anti-Neu5Gc antibody- and complement-dependent activation, and potentially contributing to human vascular pathologies. In the case of atherosclerosis, Neu5Gc is present both in endothelium overlying plaques and in subendothelial regions, providing multiple pathways for accelerating inflammation in this disease.

Pathophysiological lessons from rare associations of immunological disorders

Rare associations of immunological disorders can often tell more than mice and rats about the pathogenesis of immunologically mediated human kidney disease. Cases of glomerular disease with thyroiditis and Graves' disease and of minimal change disease with lymphoepithelioma-like thymic carcinoma and lymphomatoid papulosis were recently reported in Pediatric Nephrology. These rare associations can contribute to the unraveling of the pathogenesis of membranous nephropathy (MN) and minimal change disease (MCD) and lead to the testing of novel research hypotheses. In MN, the target antigen may be thyroglobulin or another thyroid-released antigen that becomes planted in the glomerulus, but other scenarios can be envisaged, including epitope spreading, polyreactivity of pathogenic antibodies, and dysregulation of T regulatory cells, leading to the production of a variety of auto-antibodies with different specificities [immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX syndrome)]. The occurrence of MCD with hemopathies supports the role of T cells in the pathogenesis of proteinuria, although the characteristics of those T cells remain to be established and the glomerular permeability factor(s) identified.

Familial membranous nephropathy: an X-linked genetic susceptibility?

BACKGROUND

Membranous nephropathy (MN) is the most common histological diagnosis in adults with nephrotic syndrome and a leading cause of end-stage kidney failure from glomerulonephritis. Little is known about the underlying aetiology, although anti-glomerular antibodies have been implicated. No specific underlying genetic defect has yet been identified.

METHODS

In a family with four members in three generations affected by primary MN, the serum of affected members and their mothers were assessed for anti-glomerular antibodies.

RESULTS

All four affected are male and connected through the maternal line, indicative of X-linked inheritance. Age of onset of nephrotic syndrome varied between 1 and 67 years of age, suggesting that a potential underlying gene may confer a genetic predisposition to MN, but other factors, genetic or environmental, are necessary to trigger the disease. Serologic studies revealed antibodies against glomerular and peritubular endothelial cells in the mother of the youngest patient.

CONCLUSIONS

We have identified the largest reported family with a potential X-linked susceptibility to MN. Foeto-maternal alloimmunization may have triggered the disease in the youngest individual. Considering that the majority of patients with sporadic MN are male, identification of an X-linked predisposing factor may have implications well beyond this family and could provide a target for treatment.

Target antigens and nephritogenic antibodies in membranous nephropathy: of rats and men

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in white adults. In the rat model of Heymann nephritis, the target antigen of antibodies is megalin, a multiligand receptor expressed at the podocyte cell surface. This review summarizes key findings provided by this experimental model and by our discovery of neutral endopeptidase being the alloantigen involved in neonatal cases of membranous nephropathy. We discuss the role of alloimmunization as a new mechanism of renal disease and the approach that we use to identify new podocyte antigens. We also summarize current knowledge on the mechanism of proteinuria, with special emphasis on the role of complement. In conclusion, substantial progresses have been made in understanding molecular mechanisms of membranous nephropathy, which should lead to novel therapeutic approaches.

Antiendothelial cell antibodies in vasculitis and connective tissue disease

Antiendothelial cell antibodies (AECA) are a heterogeneous family of antibodies reacting with endothelial cell antigens. These antibodies are found in various diseases and recognise several antigen determinants. Different pathophysiological effects have been observed in in vitro experiments, which include direct or indirect cytotoxicity and endothelial cell apoptosis. Furthermore, some AECA activate endothelial cells, resulting in increased leucocyte adhesiveness, activation of coagulation and vascular thrombosis. In animal models, it has been shown that AECA could promote vascular damage. Neither the endothelial cell antigens nor their precise role in the pathogenecity of different diseases in which AECA are found is well characterised. Nowadays, it is not known whether AECA are an epiphenomenon accompanying vascular injury or whether they are pathogenic. It is controversial whether fluctuations in AECA titres are associated with disease activity during follow-up studies. This review summarises the present knowledge about AECA, AECA antigens and their potential role in the pathogenecity of vasculitis and connective tissue diseases.

Molecular pathomechanisms of membranous nephropathy: from Heymann nephritis to alloimmunization

Membranous nephropathy (MN), the most common cause of idiopathic nephrotic syndrome in white adults, is characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane. In Heymann nephritis, the rat experimental model for MN, megalin--the target antigen of the nephritogenic antibodies--is expressed on the surface of podocytes, where immune complexes are formed, leading to complement activation and nephrotic-range proteinuria. However, megalin cannot be held responsible for human MN because it has not been found in human podocytes or detected in subepithelial immune deposits in patients with MN. Several potential antigens have been identified in so-called secondary forms of MN, but there is no real proof that these antigens are pathogenic. In a subgroup of infants with antenatal MN, neutral endopeptidase (NEP) has been identified as the first protein target on human podocytes of nephritogenic antibodies. The infants' mothers became immunized during pregnancy against NEP expressed on syncytiotrophoblastic cells because they were NEP deficient as a result of truncating mutations in the MME gene. Severity of neonatal renal disease was determined by the mothers' IgG response that led to the formation of the membrane attack complex of complement in the subepithelial deposits. Alloimmunization against NEP is a novel pathomechanism of MN that might also account for some cases of MN after renal or bone marrow transplantation. Other types of alloimmunization should be investigated in MN but also in other renal and nonrenal diseases, particularly those that affect the pediatric age.

Interaction of baboon anti-alpha-galactosyl antibody with pig tissues

As barriers to xenotransplantation are surmounted, such as suppression of hyperacute rejection allowing improved graft survival, it becomes important to define longer-term host-xenograft interactions. To this end we have prepared in baboons high titer anti-alpha-Galactosyl (alphaGal) and anti-porcine aortic endothelial cell antibodies, similar to human natural xenoantibodies and reactive with epitopes of thyroglobulin, laminin, and heparan sulfate proteoglycans. When injected into pigs with a protocol similar to that used in the rat to show the nephritogenic potential of heterologous anti-laminin and anti-heparan sulfate proteoglycan antibodies, baboon immunoglobulins bound first to renal vascular endothelium, and later to interstitial cells, especially fibroblasts and macrophages, and to antigens in basement membranes and extracellular matrix, where they colocalized with laminin- and heparan sulfate proteoglycan-antibodies, and with bound Griffonia simplicifolia B4. A similar binding was observed in other organs. The pigs did not develop an acute complement-dependent inflammation, but rather chronic lesions of the basement membranes and the extracellular matrix. Incubation of renal fibroblasts with baboon anti-alpha-Galactosyl antibodies resulted in increased synthesis of transforming growth factor-beta and collagen, suggesting a possible basis for the fibrotic response. The results demonstrate that in this experimental model a consequence of alphaGal antibody interaction with porcine tissues, is immunoreactivity with alphaGal on matrix molecules and interstitial cells, priming mechanisms leading to fibrosis resembling that in chronic allograft rejection. The possibility that similar lesions may develop in long-surviving pig xenografts is discussed.

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.

Glycoprotein 330/megalin (LRP-2) has low prevalence as mRNA and protein in brain microvessels and choroid plexus

Prior studies indicated that glycoprotein 330 (gp330)/megalin mediates transcytosis of apolipoprotein J (apoJ) with Alzheimer's amyloide-peptide (Abeta) across the vascular membranes of the central nervous system (CNS). Here we show the presence of gp330/megalin mRNA and gp330-like immunoepitopes in brain capillaries and choroid plexus and their absence from brain parenchyma. By polymerase chain reaction (PCR) we estimated 1.2 x 10(5) molecules (1 pg) of gp330/megalin mRNA/microg total brain capillary RNA, which is 3% of that in kidney RNA. However, gp330 mRNA was not detected by in situ hybridization in vascular CNS tissue, presumably because of low transcript prevalence. The ratio of gp330 protein:RNA was 17-fold higher in choroid plexus vs brain capillaries, which implies tissue specific regulation of the protein and mRNA prevalence. We conclude that gp330/megalin mRNA and protein are expressed in brain capillaries and choroid plexus in small amounts that are consistent with the observed activities of this endocytosing receptor in the regulation of apoJ and Abeta uptake by the CNS.

A new model of renal microvascular injury

The vascular endothelial injury with its consequent activation is actively involved in inflammation and promotion of a procoagulant state, which are likely to be of major importance in the pathogenesis of various disorders, including renal thrombotic microangiopathy. This study briefly reviews the consequences of glomerular endothelial cell injury or activation, as shown by recent experimental data.

Lupus-like nephrotropic autoantibodies in non-autoimmune mice harboring an anti-basement membrane/anti-DNA Ig heavy chain transgene

Autoantibodies target a diverse group of tissue antigens in human and experimental autoimmune nephritis. The proximal events that generate and regulate these various pathogenic Ab remain obscure. To examine the origins and fate in normal mice of autoantibodies reactive with renal basement membrane antigen, we established mice transgenic for an IgM H chain encoding an unmutated nephrotropic V region, termed LamH, derived from an MRL/lpr mouse and directed against basement membrane laminin. We previously demonstrated that in vitro transfectants combining LamH-Cmu with unmutated L chains generate distinct nephrotropic autoantibodies. Herein we report in vivo reconstruction of diverse pathogenic autoreactivity by association of LamH-Cmu with endogenous L chains. Progeny of one founder, termed M7, express a distinct phenotype characterized by minimal B cell mIgM and spontaneous production of LamH-Cmu autoreactivity. Similar Ab were not recovered from two phenotypically distinct transgenic lines expressing abundant transgene mIgM. The results suggest that lupus-like autoantibodies are readily generated in the normal genetic background by random recombinatorial events in the absence of mutation and that these Ab may contribute to disease if normal regulation is disturbed.

Specificity, pathogenecity, and clinical value of antiendothelial cell antibodies

OBJECTIVE

To characterize the putative target antigens for antiendothelial cell antibodies (AECA), the possible pathophysiological role of AECA, and the clinical value of these antibodies as markers of disease activity.

METHODS

A structured literature search was done using Medline in combination with a manual search. Two physicians reviewed all articles of special interest.

RESULTS

AECA are a heterogenous group of antibodies directed against a variety of antigen determinants on endothelial cells (EC). The EC antigens can be constitutively expressed, constitutively expressed and modulated by cytokines, or cryptic. In addition, antigen determinants for AECA may also be molecules that adhere to EC ("planted" antigens). However, many AECA antigens are currently not well characterized. AECA are detected in a wide variety of inflammatory disorders. Although probably of limited value in disease diagnosis, the detection of these antibodies may be valuable in following disease activity. In several diseases such as systemic lupus erythematosus and systemic vasculitis, high AECA titers are found during active disease whereas lower titers or disappearence of AECA have been reported during remission. The correlation between changes in AECA titers and disease activity suggests an important role for AECA in processes in which vessel wall damage occurs, although it does not exclude the possibility that AECA are an epiphenomenon of vascular injury. Several recent in vitro studies support a role of AECA in the pathophysiology of these inflammatory disorders. AECA may play a role in the pathophysiology by inducing activation of EC resulting in upregulation in the expression of endothelial adhesion molecules and/or secretion of chemoattractants and cytokines. An alternative mechanism by which AECA could be a trigger in the pathogenesis of some diseases is complement dependent cytotoxicity (CDC) and/or antibody dependent cellular cytotoxicity (ADCC). In experimental animal models, antibodies to antigenic determinants expressed on EC were capable of inducing vascular injury.

CONCLUSION

AECA represent a heterogenous group of antibodies directed against a variety of antigenic determinants on EC. They are present in a variety of inflammatory disorders. The detection of these antibodies may be valuable in following disease activity. Further characterization of putative antigens is needed to better understand their pathophysiological role.

A new model of renal microvascular endothelial injury

Although the importance of injury with consequent activation of endothelium is well-recognized in diseases affecting the glomerular endothelial cell (GEN), research on GEN injury in vivo has been hampered by the lack of adequate animal models. Here we report the establishment and characterization of a new GEN injury model in rats. This model was induced by selective renal artery perfusion with anti-GEN IgG and resulted in the severe acute renal failure with marked platelet deposition and development of a thrombotic microangiopathy involving glomeruli. Peritubular capillary endothelial cells were also damaged that was associated with severe tubular necrosis. Although the glomerular changes were severe, half of the glomeruli recovered by day 10, while interstitial changes remained throughout our observation time course. Proliferation of GEN was observed during the recovery phase. An increased expression of endothelial nitric oxide synthase in GEN was also observed, and may be an adaptive mechanism to counteract the thrombosis and ischemia. This model should be useful to investigate the pathophysiology of renal microvascular diseases and the mechanisms of GEN injury, activation and recovery in vivo.

Primary kidney cells

Primary rabbit kidney epithelial cell cultures can be obtained that express renal proximal tubule functions. Toward these ends, renal proximal tubules are purified from the rabbit kidney by the method of Brendel and Meezan. To summarize, each kidney is perfused with iron oxide, which becomes associated with glomeruli. The renal cortex is sliced and homogenized to liberate nephron segments. Renal proximal tubules and glomeruli are purified by sieving. The glomeruli, covered with iron oxide, are removed using a magnet. After a brief collagenase treatment (to disrupt basement membrane), the tubules are plated in hormonally defined serum-free medium supplemented with 5 μg/mL bovine insulin, 5 μg/mL human transferrin, and 5 × 10⁻⁸M hydrocortisone. After 5–6 d of incubation, confluent monolayers are obtained that possess multicellular domes, indicative of their capacity for transepithelial solute transport.

In vivo modulation of CD26 (dipeptidyl peptidase IV) in the mouse: effects of polyreactive and monoreactive antibodies

We previously reported that intravenous injections in rabbits or guinea pigs of divalent antibodies to purified protein or carbohydrate antigens located mainly on endothelial cells induce acute pulmonary edema, which is often lethal. Surviving animals develop resistance to the injurious effect of subsequent injection of antibodies (adaptation), associated with shedding of antigen-antibody complexes from endothelial cells. In the present study, we investigated and compared in mice the effects of 3-day multiple injections of two different rabbit antibody (IgG) preparations against antigens expressed mainly at the surface of epithelial cells. The first preparation contained antibodies to a single transmembrane protein, CD26 (dipeptidyl peptidase IV [DPP IV]) (monoreactive anti-DPP IV IgG); the second contained antibodies against multiple antigens of the renal tubular brush border (BB), including DPP IV (polyreactive anti-BB IgG). Both IgG preparations caused loss of DPP IV from the organs studied, as shown by reduction in enzyme activity in tissue homogenates and by immunofluorescence microscopy, which showed loss of DPP IV from cell surface. However, the monoreactive anti-DPP IV IgG induced considerably greater reduction than polyreactive anti-BB IgG. Loss of DPP IV from the cell surface probably occurred by shedding of immune complexes into vascular and extravascular fluids, including bile and urine. The results may have relevance to hyperacute rejection of xenografts, as from pigs to primates. Since human natural antibodies that bind to porcine cells are polyreactive, a new prophylactic strategy for hyperacute rejection might be based on down-regulation of the major xenogeneic antigen, alpha-galactosyl, by injecting donor animals with monoreactive alpha-galactosyl antibodies before transplantation.

Glycoprotein 330/megalin: probable role in receptor-mediated transport of apolipoprotein J alone and in a complex with Alzheimer disease amyloid beta at the blood-brain and blood-cerebrospinal fluid barriers

A soluble form of Alzheimer disease amyloid beta-protein (sA beta) is transported in the blood and cerebrospinal fluid mainly complexed with apolipoprotein J (apoJ). Using a well-characterized in situ perfused guinea pig brain model, we recently obtained preliminary evidence that apoJ facilitates transport of sA beta (1-40)-apoJ complexes across the blood-brain barrier and the blood-cerebrospinal fluid barrier, but the mechanisms remain poorly understood. In the present study, we examined the transport process in greater detail and investigated the possible role of glycoprotein 330 (gp330)/megalin, a receptor for multiple ligands, including apoJ. High-affinity transport systems with a Km of 0.2 and 0.5 nM were demonstrated for apoJ at the blood-brain barrier and the choroid epithelium in vivo, suggesting a specific receptor-mediated mechanism. The sA beta (1-40)-apoJ complex shared the same transport mechanism and exhibited 2.4- to 10.2-fold higher affinity than apoJ itself. Binding to microvessels, transport into brain parenchyma, and choroidal uptake of both apoJ and sA beta (1-40)-apoJ complexes were markedly inhibited (74-99%) in the presence of a monoclonal antibody to gp330/megalin and were virtually abolished by perfusion with the receptor-associated protein, which blocks binding of all known ligands to gp330. Western blot analysis of cerebral microvessels with the monoclonal antibody to gp330 revealed a protein with a mass identical to that in extracts of kidney membranes enriched with gp330/megalin, but in much lower concentration. The findings suggest that gp330/megalin mediates cellular uptake and transport of apoJ and sA beta (1-40)-apoJ complex at the cerebral vascular endothelium and choroid epithelium.

Angiotensin II is mitogenic for cultured rat glomerular endothelial cells

Angiotensin II (Ang II) has growth-stimulatory properties on different renal cell types. However, possible growth effects of this vasoactive peptide on endothelial cells isolated from the glomerular microvasculature have not been formally investigated. Therefore, we isolated and characterized primary cultures of rat glomerular endothelial cells. We used a simple technique in which collagenase-treated glomeruli were sparsely plated in several 96-well culture plates and microscopically screened for cobblestone-like outgrowth. After two limiting dilutions, homogeneous cultures were obtained. Cells were characterized by positive staining for the endothelial markers factor VIII, CD 31, endothelial leukocyte adhesion molecule-1, and the lectin Bandeiraea simplificifolia. Ang II stimulated the synthesis and release of endothelin-1 in culture supernatants. Moreover, in contrast to syngeneic mesangial cells, glomerular endothelial cells expressed angiotensin-converting enzyme. Ang II stimulated a mild but significant proliferation of quiescent cells, as measured by [3H]thymidine incorporation and direct cell counting. This mitogenesis was transduced by losartan-blockade angiotensin type 1 receptors. Moreover, Ang II mediated phosphorylation of mitogen-activated protein kinase 2 and induction of transcripts for the immediate early gene Egr-1. Our results indicate that Ang II is a moderate mitogen for primary cultures of rat glomerular endothelial cells and activation of these metabolically active cells may play a role in the pathophysiology of several types of glomerulonephritis. Moreover, remodeling of glomerular endothelial cells by Ang II may be important in the progression of structural renal damage during the course of hypertensive injury.

Interaction of antibody with Forssman antigen in guinea pigs. A mechanism of adaptation to antibody- and complement-mediated injury

Forssman antigen is a glycosphingolipid with antigenic specificity determined by extra-membrane haptenic sugars similar to blood group antigens and antigens that are the main barrier to xenogeneic organ transplantation. Herein, we describe the localization of Forssman antigen in guinea pig lungs and kidneys and the consequences of its interaction with antibodies in vitro and in vivo (Forssman reaction). Exposure of cultured guinea pig aortic endothelial cells to Forssman antibodies induced rapid redistribution of antigen-antibody complexes at the cell surface, followed by shedding that occurred by blebbing of plasma membrane as vesicles or fragments, and was associated with disappearance of antigen from the cell surface (antigenic modulation). Guinea pigs surviving frequent intravenous infections of increasing amounts of antibodies, for a total of 20 to 40 lethal doses, developed a partial or complete adaptation to generalized Forssman reaction, and adaptation was associated with partial or complete modulation of Forssman antigen at the surface of the pulmonary and, in minor degree, renal endothelial and epithelial cells. These findings support the hypothesis that modulation of endothelial carbohydrate antigens contributes to adaptation of highly vascularized organs exposed to tolerable levels of allo- or xenoantibodies.

Clinicopathologic associations of anti-endothelial cell antibodies in immunoglobulin A nephropathy and lupus nephritis

Sera from 45 patients with lupus nephritis (LN), 63 patients with immunoglobulin A nephropathy (IgA N), and 71 glomerulonephritic controls (including 44 mesangial proliferative glomerulonephritis cases, 14 membranous glomerulonephritis cases, and 13 focal segmental glomerular sclerosis cases), and from 33 normal control subjects were tested by a cellular enzyme-linked immunoabsorbent assay for their anti-endothelial cell antibody (AECA) activity. Compared with normal controls, AECAs of the IgG subtype (AECA-IgG) were detected in LN (P < 0.001) and AECAs of the IgA subtype (AECA-IgA) were detected in both IgA N and LN (P = 0.018 and P < 0.001, respectively). Binding activity of AECA to endothelial cells was inhibited by endothelial cell lysate and fibroblast lysate but not by lymphocyte lysate, double stranded-DNA, or bovine serum albumin. Anti-endothelial cell antibody-positive sera also reacted with fibroblasts. In IgA N, associations were found between the presence of AECA and younger age (P = 0.036), proportion of crescents greater than 10% (P = 0.016), fibrin crescents (P = 0.016), and focal and segmental necrotizing lesions (P = 0.047). In LN, inverse associations were found between the presence of AECA and the duration of disease (P = 0.021), elevated serum creatinine levels (P = 0.020), decreased creatinine clearance (P = 0.043), and frequency of chronic renal failure (P = 0.036). Positive associations were observed between the presence of AECA and active lupus (P = 0.017), anti-nuclear antibodies (P = 0.015), and anti-DNA antibodies (P = 0.041). Our results suggest that AECA may be linked with the pathogenesis of LN and IgA N.

Divalency of the monoclonal antibody 5-1-6 is required for induction of proteinuria in rats

A single i.v. injection of 3 mg of the F(ab')2 fragment of MoAb 5-1-6 into rats induced immediate proteinuria (128.1 +/- 80.7 mg/24 h on day 1) which lasted 1-2 days. In contrast, rats administered 10 mg of the corresponding Fab fragment did not develop abnormal proteinuria even though an equivalent dose of the intact MoAb 5-1-6 far exceeded the nephritogenic dose. The total kidney binding of 125I-Fab fragment was 209.5 +/- 34.3 micrograms/2 kidneys. This exceeded that obtained by injection of 3 mg MoAb 5-1-6 IgG1 (58.9 +/- 12.5 micrograms/2 kidneys at 1 h) and was similar to that obtained following injection of 3 mg F(ab')2 fragment (235.3 +/- 16.9 micrograms/2 kidneys). Immunofluorescence (IF) showed a linear pattern along the glomerular capillary wall at 1 h after the administration of MoAb 5-1-6 IgG1, F(ab')2 or Fab fragment. On day 5, fine to coarse granules were observed scattered in F(ab')2-injected rat glomeruli, whereas granules were densely localized in Fab-injected rat glomeruli. Complement-depleted rats injected with 3 mg of MoAb 5-1-6 IgG1 developed proteinuria with the same time course as non-depleted rats. This observation, together with the ability of F(ab')2 to induce proteinuria, indicates that proteinuria induced by MoAb 5-1-6 is complement-independent. This study suggests that MoAb 5-1-6-induced proteinuria is initiated by cross-linking of the epitopes by divalent MoAb 5-1-6 and is independent of complement activity.

Intraglomerular basement membrane translocation of immune complex (IC) in the development of passive in situ IC nephritis of rats

A study was performed to elucidate the mechanisms of charge-based immune complex nephritis. A chronological observation after induction of nephritis was made by immunoelectron microscopy to clarify whether antigen (Ag) remains in association with antibody (Ab) and C3 during the translocation through the glomerular basement membrane (GBM). Fifteen minutes after intrarenal perfusion with cationized ferritin (pI > 10.0) as Ag, followed by injection of rabbit anti-ferritin Ab, deposition of subendothelial Ag-Ab-C3 complexes was observed. Between 2 hours and 1 day, a large number of Ag in close association with Ab was noted in the lamina densa, but only a small amount of C3 was detectable. During this time Ag and Ab in the subendothelial region gradually decreased. However, C3 reappeared in the subepithelial region together with the Ag-Ab complex after 1 day, and the subendothelial C3 significantly decreased. At 2 hours and day 1, the distributions of Ag and Ab in the GBM were similar in immersion-fixed kidneys regardless of the preperfusion with phosphate-buffered saline. On the other hand, the passage of Ag across the lamina densa was delayed in the experimental rats as compared with the controls. Significant albuminuria also appeared on day 1. Despite the general concept that Ab binding to cationized Ag results in low avidity immune complex, cationized Ag translocated across the GBM in close association with Ab. The complement was activated biphasically in the subendothelial and in the subepithelial space. The subendothelial complement activation may have contributed to the translocation of immune complex.

Antibodies to intercellular adhesion molecule 1/lymphocyte function-associated antigen 1 prevent crescent formation in rat autoimmune glomerulonephritis

In patients with glomerulonephritis widespread crescents are associated with a poor prognosis. Crescent formation appears to depend on the migration of mononuclear cells into Bowman's space, and therefore the interaction between leukocytes and glomerular endothelium may be a critical event in the genesis of crescents. We performed the present study to determine the effects of mouse monoclonal antibodies to the adhesion molecules intercellular adhesion molecule 1 (ICAM-1) and lymphocyte function-associated antigen 1 (LFA-1) in a model of crescentic glomerulonephritis in Wistar-Kyoto rats, induced by immunization with bovine glomerular basement membrane (GBM). By 10-14 d after immunization, the rats had developed circulating anti-GBM antibodies, reactive with the alpha 3 chain of type IV collagen (the Goodpasture antigen), accompanied by proteinuria, accumulation of rat immunoglobulin (Ig)G in the GBM, increased expression of ICAM-1 by glomerular endothelial cells, infiltration of glomerular tufts with LFA-1+ T cells and monocyte/macrophages, and early crescents. At 5 wk all rats had diffuse fibrocellular crescents, glomerular sclerosis, and tubulointerstitial damage. All rats developed severe renal insufficiency and died by 5 or 6 wk. The administration of monoclonal antibodies to rat ICAM-1 and LFA-1 markedly decreased the severity of the renal disease. In a group of rats injected three times a week with the monoclonal antibodies, from 2 d before immunization with GBM to day 14, glomerular abnormalities and proteinuria were virtually absent at day 14; even at 5 wk glomerular disease was quite mild, with only slight crescent formation and with only a mild decrease in renal function. When treatment was continued until 5 wk, the beneficial effects were even more marked, with virtual absence of crescents and with preservation of normal renal function. In a group of rats in which treatment was initiated on day 14, shortly after the appearance of glomerular abnormalities, progression of the disease was appreciably retarded, and the decrease in renal function was inhibited. The kidneys of rats treated from days -2 to 14 with antibodies to ICAM-1 and LFA-1 showed bright linear staining for rat IgG along the GBM, which did not differ in intensity from that seen in untreated rats. Furthermore, the titers of anti-GBM antibodies at 2 wk in treated rats were not lower than that seen in most of the untreated rats. There was, however, moderate reduction of anti-GBM antibodies at 5 wk in the treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Endothelial cell destruction by polymorphonuclear leukocytes incubated with sera from patients with systemic lupus erythematosus (SLE)

When normal polymorphonuclear leukocytes (PMN) were incubated with sera from patients with active systemic lupus erythematosus (SLE), a significantly increased cytotoxicity against human cultured vascular endothelial cells (EC), compared with normal control sera, was demonstrated by the standard 51Cr release method. The degree of this cytotoxicity was correlated with the immune complex level in each serum. The cytotoxicity did not correlate with the presence of anti-EC antibody. An absorption study with C1q-Sepharose 4B further suggested that the immune complexes are the factor which induce cytotoxicity. A gel fractionation study, however, indicated the heterogenity of the cytotoxic activity, and suggested the possible contribution of other substances including anti-EC, at least in some of the patients. This type of cytotoxicity may initiate the inflammatory process including vascular damage of the disease.

Mechanisms of clearance of immune complexes from peritubular capillaries in the rat

These experiments evaluated extraglomerular sites of renal immune complex (IC) deposition and specific features of host capability to remove these IC. Ex vivo perfusion of rat kidneys with the endothelium binding lectin concanavalin A (con A) followed by rabbit anti con A IgG results in a subendothelial IC nephritis in glomerular capillaries (GC) and diffuse IC formation with complement (C3) deposition in peritubular capillaries (PC). Histologic, immunofluorescence, and ultrastructural studies were performed at 10 minutes and 1, 4, and 24 hours after perfusion. At 10 minutes, strong linear binding of con A, rabbit IgG, and rat C3 to the endothelium was detected by immunofluorescence in both GC and PC. In GC this was followed by endothelial cell swelling and denudation (1 hour) with platelet and neutrophil infiltration and formation of subendothelial IC deposits which persisted at 4 and 24 hours. In contrast, some PC endothelial swelling was also present at 10 minutes and 1 hour, but ICs (IgG, con A, C3) were capped and shed into capillary lumina at 1 to 2 hours with complete clearance of IC by 4 hours. Selective neutrophil depletion, by antisera and irradiation, and complement depletion with cobra venom factor, delayed clearance of PC IC by several hours but complete clearance of IC with restored structural integrity of PC was still achieved by 24 hours. Platelet depletion had no effect on PC IC clearance. These studies demonstrate a model for study of PC IC. Such a model may aid our understanding of lupus nephritis in which extensive GC IC deposits associated with severe inflammatory injury may coexist with PC deposits. Efficient clearance of IC in PC compared with GC may be due to differences in hemodynamic forces, amounts of IC formed in each of these sites, differences in binding of IC to subendothelial basement membrane, or phenotypic specialization of the endothelium lining these two different capillary beds.

Antibodies to endothelial cells in systemic lupus erythematosus: a potential marker for nephritis and vasculitis

Using an ELISA, anti-endothelial cell antibodies (AECA) have been found in sera obtained at the time of renal biopsy in 46 out of 57 patients (81%) with systemic lupus erythematosus (SLE) and nephritis (mean binding index (BI) = 84% +/- 52.8) compared with 22 out of 50 SLE patients (44%) without nephritis (mean BI = 45% +/- 35.9). Seventy normal human sera had a mean BI of 10% +/- 9.8. The highest levels were seen in patients with diffuse proliferative glomerulonephritis (WHO grade IV) and in patients with proteinuria and nephrotic syndrome. When the biopsies were assessed for activity and chronicity scores, AECA were associated with active renal lesions (P less than 0.001). AECA levels correlated with low complement levels but not with anti-DNA antibodies to extractable nuclear antigens (ENA), anti-cardiolipin or anti-neutrophil cytoplasmic antibodies. The presence of AECA conferred a positive predictive value of 0.68 for the presence of nephritis. Twenty-five patients had active vasculitis at the time of assay and the highest AECA values were seen in patients with both nephritis and vasculitis. No correlation was seen with serum immunoglobulin levels and immune complexes did not bind significantly to the endothelial surface. The possible role of these antibodies as a marker in lupus nephritis is discussed.

A role for DNA in anti-DNA antibodies binding to endothelial cells

Vascular injury and microvascular thrombosis are prominent features of systemic lupus erythematosus, as are circulating DNA-binding antibodies (DNAb). Experimental glomerulonephritis can be induced by anti-endothelial cell antibodies, and polyreactive DNAb might be pathogenetic by binding to endothelial cells, perhaps influencing their non-thrombogenic nature. To test this hypothesis, eight monoclonal antibodies (mAb) that bind to DNA derived from (NZB x NZW)F1 or MRL/Mp-lpr/lpr mice, were tested for their ability to bind to human umbilical vein endothelial cells (HUVEC). Binding was assessed using flow cytometry, fluorescence microscopy and cellular ELISA. Three of the eight mAb, at concentrations employed in this study, bound to HUVEC and dermal fibroblasts. Of these three mAb, one bound also to platelets. Two of the three demonstrated strong binding to (1) freshly isolated, collagenase-digested HUVEC, (2) 2nd passage HUVEC in suspension after trypsinization and, (3) 2nd passage HUVEC growing on plastic plates. To determine whether DNA itself acted as a ligand in this binding, prior treatment with DNAase was studied. Treatment of the endothelial cells with DNAase had no effect on the binding of one mAb, but DNAase treatment of this monoclonal itself resulted in a 60% reduction in binding to HUVEC, suggesting that the binding might be mediated through DNA in the form of a DNA/anti-DNA immune complex. In contrast, DNAase digestion of the endothelial cells caused a 40% reduction in the binding of the other two monoclonal antibodies. Furthermore, one of the two mAb bound 30% more to HUVEC after themselves being subjected to DNAase treatment. These two monoclonals may therefore be binding directly to HUVEC, possibly to DNA associated with the membrane. Prior DNAase digestion of dermal fibroblasts had a more profound effect on the binding of all three autoantibodies compared to HUVEC after similar treatment. Therefore, DNA can bind independently to either antibody or cell, thus supporting build up of complexes and capture of preformed complexes. Functionally, the binding of mAb to HUVEC did not influence thrombin-induced prostacyclin synthesis, in contrast to a control monoclonal anti-endothelial cell antibody EN4, which did.

Acute glomerulonephritis in a patient with Rocky Mountain spotted fever

It is generally assumed that acute tubular necrosis is the etiology of renal failure that can occur during the course of Rocky Mountain spotted fever (RMSF). However, histologic examination of kidneys has been mainly limited to autopsy cases of fulminant infections. Acute glomerulonephritis due to glomerular immune complex deposition has not been reported in RMSF. We describe a case of acute oliguric renal failure that developed more than 2 weeks following the onset of RMSF. Renal biopsy showed acute glomerulonephritis with inflammatory cell infiltration and subendothelial immune deposits. Thus, acute glomerulonephritis should be in the differential diagnosis of acute renal failure that occurs in RMSF.

Formation of subepithelial dense deposits in rats induced by a monoclonal antibody against the glomerular cell surface antigen

We developed a monoclonal antibody, H5H3, of IgG1 subclass by hybridization technique using spleen cells of mice immunized with plasma membrane fraction of isolated rat glomeruli. H5H3 recognized main bands at about 220 kD by immuno-overlay technique and bound to the glomerulus as well as brush border of proximal tubules by indirect immunofluorescence (IF) microscopy on normal rat kidney frozen sections. By immunoelectron microscopy (IEM) it bound to the surface of mainly glomerular epithelial cell and weakly to the endothelial cell. After injection to Wistar rats it remained granularly in the glomerulus for more than 2 weeks seen by IF. When rats were preimmunized with murine IgG 4 days before the injection of H5H3, mouse IgG, rat IgG and C3 were strongly visible granularly in the glomerulus in 14 days by IF. Numerous dense deposits were formed at subepithelial area seen by transmission electron microscopy. Perfusion experiment of H5H3 into rat left kidney showed granular distribution of mouse IgG in 48 h, indicating that the reaction occurred in situ. H5H3 bound diffusely in fine granular pattern on the surface of cultured glomerular epithelial cells (GEC) studied by IF and IEM. Antigenic redistribution occurred on GEC after incubation of H5H3 at 37 C. These results suggested the required conditions to form subepithelial immune dense deposits, namely that H5H3 after reaction with antigen could stay for long time in the glomerulus; that H5H3 became an antigen in autologous phase to induce large immune complexes; and H5H3 could induce antigenic modulation.

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.

Binding of monoclonal antibodies to glomerular endothelium, slit membranes, and epithelium after in vivo injection. Localization of antigens and bound IgGs by immunoelectron microscopy

The antigens recognized by seven monoclonal antibodies (MAbs) raised against rat glomerular proteins were localized, and the sites of binding of the MAbs after in vivo injection were determined by immunoelectron microscopy. The antigens were localized in situ by immunoperoxidase and immunogold labeling to different domains and microdomains of the glomerular endothelium and epithelium. 23A recognized an antigen expressed exclusively on the luminal (apical) domain of the endothelium. 5A (anti-podocalyxin) and 26C (anti-DPPIV) recognized antigens expressed on the apical domains of both the endothelium and podocytes. 13A, 14A, 20B (anti-gp330), and 27A recognized antigens restricted to podocytes in the glomerulus. The 13A antigen was present on their basal surface and the 27A and 14A antigens were expressed on both their apical and basal domains. The 14A antigen also was associated with the filtration slit membranes. All these MAbS bound to their antigens after injection in vivo. Those that recognize endothelial antigens were rapidly cleared from the circulation and rapidly disappeared from glomeruli, whereas those that recognize epithelial antigens persisted in the circulation and were detectable in glomeruli for hours or days. The sites of binding of the MAbs differed: 23A and 5A IgG (antipodocalyxin) bound exclusively to the luminal domain of the endothelium, whereas 26C IgG (anti-DPPIV) bound to both the luminal endothelial membrane and the apical and basal domains of podocytes. The MAbs that recognize podocyte antigens bound to different domains of the podocyte plasmalemma: 13A and 27A IgGs to the basal domain, 14A to the slit membranes, and 20B to coated pits on the entire plasma membrane. 27A IgG led to the formation of small subepithelial immune deposits that remained up to 10 days. It is concluded that 1) glomerular membrane proteins vary considerably in their distribution among plasmalemmal domains and microdomains of endothelial and epithelial cells; 2) virtually all structures in the glomerulus and all domains and micro-domains of the endothelium and podocyte are accessible to circulating antibodies; and 3) the fate of immune complexes formed by binding to glomerular components varies with the location of the antigen within the glomerulus, with those that bind to the basal domain and slit membranes of the podocyte persisting longer than the others.

Anti-vascular endothelial cell antibodies in severe preeclampsia

There is mounting evidence to suggest that vascular endothelial cell injury plays an important role in the pathogenesis of preeclampsia. In this study an enzyme-linked immunoassay was used to demonstrate increased binding of immunoglobulins G and M to human umbilical vein endothelial cells by sera from women with severe preeclampsia as compared with normal pregnant control women. Fifty percent of women with preeclampsia versus 15.4% of control women had either immunoglobulin G or immunoglobulin M binding. In addition, immunofluorescent staining of normal renal cortical tissue with preeclamptic sera showed increased binding of immunoglobulin G to arterioles in patients with anti-vascular endothelial cell antibodies. These antibodies were not directed at HLA antigens and did not cross react with platelets. Interferon-gamma stimulation did not increase immunoglobulin binding. Antibodies to antigens expressed on vascular endothelial cells may be important in mediating the endothelial damage seen in preeclampsia.

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.

Primary cultures of rabbit renal proximal tubule cells: I. Growth and biochemical characteristics

Before the usefulness of a new in vitro model can be ascertained, the model must be properly defined and characterized. This study presents the growth rate and biochemical characteristics of rabbit renal proximal tubule cells in primary culture over a 2-wk culture period. When grown in a hormonally defined, antibiotic-free medium these cells form confluent monolayer cultures within 7 d after plating. Multicellular dome formation, an indicator of transepithelial solute transport, was expressed after confluent cultures were formed. The activity of the cytosolic enzyme, lactate dehydrogenase, and the lysosomal enzyme, N-acetyl-glucosaminidase, increased 14- and 2-fold during the first 8 d of culture, respectively. In contrast, the activity of a brush border enzyme, alkaline phosphatase, decreased 85% within the first 8 d of culture. Release of these enzyme markers into the culture medium, which are routinely used to measure cytotoxicity, stabilized after 8 d in culture. The ratio of cellular protein to DNA changed according to the state of cellular growth. Values rose from 0.035 mg protein/micrograms DNA in preconfluent cultures to 0.059 mg protein/micrograms DNA in confluent cultures. These results document the characteristics of a primary proximal tubule cell culture system for future studies in in vitro toxicology.

Primary rabbit kidney proximal tubule cell cultures maintain differentiated functions when cultured in a hormonally defined serum-free medium

A primary rabbit kidney epithelial cell culture system has been developed which retains differentiated functions of the renal proximal tubule. In addition, the cells have a distinctive metabolism and spectrum of hormone responses. The primary cells were observed to retain in vitro a Na+-dependent sugar transport system (distinctive of the proximal segment of the nephron) and a Na+-dependent phosphate transport system. Both of these transport processes are localized on the apical membrane of proximal tubule cells in vivo. In addition, probenicid-sensitive p-aminohippurate (PAH) uptake was observed in basolateral membranes of the primary tubule cells, and the PAH uptake by these vesicles occurred at a rate that was very similar to that observed with membranes derived from the original tissue. Several other characteristics of the primary cells were examined, including hormone-sensitive cyclic AMP production and phosphoenolpyruvate carboxykinase (PEPCK) activity. Like the cells in vivo, the primary proximal tubule cells were observed to produce significant cyclic AMP in response to parathyroid hormone, but not in response to arginine vasopressin or salmon calcitonin. Significant PEPCK activity was observed in the particulate fraction derived from a homogenate of primary rabbit kidney proximal tubule cells.

De novo membranous glomerulonephropathy in renal allografts: a report of ten cases and review of the literature

De novo posttransplantation membranous glomerulonephropathy (MGN) is the most common form of de novo glomerulopathy in renal allografts. The clinical and pathological features of ten patients with de novo MGN were studied and the related literature was reviewed to assess the clinical features, morphologic characteristics, and natural course of this disease. De novo MGN may occur in both living related and cadaveric allografts at any time after transplantation. It presents clinically either as asymptomatic proteinuria or the nephrotic syndrome, a feature of poor prognostic implication. Morphologically, de novo MGN in most instances has distinct differences from idiopathic MGN in native kidneys and is accompanied by varying features of rejection. About 50% of grafts which develop de novo MGN eventually fail. This rather poor outcome may not represent the natural history of de novo MGN per se but rather the consequences of associated chronic rejection. Evidence is presented that many of the cases of so-called de novo MGN may be a complication of transplant glomerulopathy rather than being caused by mechanisms totally independent from rejection.

Development of immune complexes in the skin

Complement activation by immune complexes induces inflammation, but during this process the nature of the complexes is altered. Once immune complexes have attained sufficient lattice to activate complement, further increase of the lattice and immune precipitation are limited by the incorporation of complement components. The presence of complement components in immune complexes facilitates their disposal from circulation by complement receptors on red cells in humans. Without complement activation the disposal of immune complexes of sufficient lattice is mediated by Fc receptors. The development of immune deposits in tissues can arise by several mechanisms. Circulating immune complexes may be deposited in a number of vascular beds. Immune deposits in tissues may also arise by local formation. This process may involve structural antigens in tissues, cell surface antigens that are shed after interaction with specific antibodies or antigens that have become planted in tissues and then combine with antibodies. Charge-charge interactions enhance deposition of immune complexes in several organs, involving fixed negative charges in tissues and positive charges on antigens or antibodies in immune complexes. Successful detection of immune deposits in dermal vessels requires the examination of fresh lesions. Local vascular changes contribute significantly to deposition of immune complexes in dermal vessels. Charge-charge interactions enhance this deposition and contribute to the development of deposits at the dermal-epidermal junction in experimental animals.

Antiglomerular basement membrane nephritis in beige mice. Deficiency of leukocytic neutral proteinases prevents the induction of albuminuria in the heterologous phase

Antiglomerular basement membrane (GBM) nephritis with massive albuminuria can be induced in mice by injection of heterologous antibodies against mouse GBM. The albuminuria and the glomerular lesions in this model are not mediated by complement, but are dependent on the presence of polymorphonuclear granulocytes (PMN) in the glomeruli. Neutral serine proteinases and reactive oxygen metabolites produced by activated PMN have been implicated as agents contributing to tissue damage. We examined the role of leukocytic neutral proteinases by comparing the glomerular damage and albuminuria after injection of rabbit anti-mouse GBM antibodies in normal control mice (C57BL/6J, +/+) and in beige mice (C57BL/6J,bg/bg) in which PMN are deficient of the neutral proteinases elastase and cathepsin G. The dose-dependent albuminuria that occurred in control mice after injection of 1.4-22 mg of anti-GBM antibodies was not observed in beige mice, despite a comparable influx of PMNs in the glomeruli. By electron microscopy both strains showed a similar attachment of PMN to the denuded GBM together with swelling and necrosis of endothelial cells. Elastase activity of extracts from PMN of beige mice was only 10-15% of the activity of control mice. In vitro, GBM degradation by PMN extracts of beige mice was 70% lower than that seen in control experiments. PMNs of beige and control mice showed no differences in superoxide production. In addition, administration of scavengers of reactive oxygen metabolites, such as catalase and desferrioxamine, did not prevent the albuminuria in this model. These findings support the important contribution of leukocytic neutral proteinases to the induction of albuminuria in the acute phase of anti-GBM nephritis in the mouse.

Immunologic approaches to blockade of the renin-angiotensin system: a review

Several immunologic approaches to blockade of the renin-angiotensin system (RAS) have been reported, involving most of the proteins and peptides of the biochemical cascade: renin, substrate, angiotensins, and converting enzyme. None as yet has involved blockade of angiotensin II receptors. Earlier and more recent studies used passive transfer of heterologous antibodies or active immunization against RAS proteins and peptides. Passive transfers have been performed with both polyclonal antibodies and now with specific monoclonal immunoglobulins. The latter are better defined in affinity, quantity, and capacity to bind and thus inhibit the biologic activity of the antigen. Active immunization produced long-term blockade of part or all of the biologic activity of the system. The immunopathologic consequences of the use of antibodies raised against a self-antigen could be of interest in defining the predominant site of storage and secretion of the relevant protein and hence the respective roles of different tissues in the production of specific proteins in, for example, the vascular pulmonary bed for converting enzyme and renal arterial tree for renin. In all cases immunologic methods offer in vivo experimental models of short- or long-term RAS blockade that could be compared with pharmacologic methods, such as converting-enzyme inhibition, angiotensin II antagonists, and renin inhibitors.

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.