RANTES and monocyte chemoattractant protein-1 (MCP-1) play an important role in the inflammatory phase of crescentic nephritis, but only MCP-1 is involved in crescent formation and interstitial fibrosis

The involvement of chemokines in inflammation is well established, but their functional role in disease progression, and particularly in the development of fibrosis, is not yet understood. To investigate the functional role that the chemokines monocyte chemoattractant protein-1 (MCP-1) and RANTES play in inflammation and the progression to fibrosis during crescentic nephritis we have developed and characterized a murine model for this syndrome. Significant increases in T-lymphocytes and macrophages were observed within glomeruli and interstitium, paralleled by an induction of mRNA expression of MCP-1 and RANTES, early after disease initiation. Blocking the function of MCP-1 or RANTES resulted in significant decreases in proteinuria as well as in numbers of infiltrating leukocytes, indicating that both MCP-1 and RANTES (regulated upon activation in normal T cells expressed and secreted) play an important role in the inflammatory phase of crescentic nephritis. In addition, neutralization of MCP-1 resulted in a dramatic decrease in both glomerular crescent formation and deposition of type I collagen. These results highlight a novel role for MCP-1 in crescent formation and development of interstitial fibrosis, and indicate that in addition to recruiting inflammatory cells this chemokine is critically involved in irreversible tissue damage.

Effects of omega-3 fatty acids on complement-mediated glomerular epithelial cell injury

To define the mechanisms by which fish oil protects rats with passive Heymann nephritis (PHN) from proteinuria in vivo, we investigated whether omega-3 fatty acid substitution of glomerular epithelial cells (GEC) in culture alters their susceptibility or response to complement-mediated sublethal injury. The results show that GECs can be cultured under conditions that effectively incorporate omega-3 or omega-6 fatty acids into membrane phospholipids without causing toxicity. Under these conditions, sublethal injury with anti-Fx1A and C5b-9 stimulated a 6.6-fold increase in TxA2 production by GECs substituted with arachidonic acid (AA, omega-6) but no increase was detected in eicosapentaenoic acid (EPA, omega-3) substituted cells. Sublethal cell membrane injury was of equal severity in both groups as measured by the release of preloaded biscarboxyethyl carboxyfluorescein and by the transepithelial flux of albumin. In addition, omega-3 and omega-6 fatty acid substituted cells showed similar increases in diacylglycerol mass in response to sublethal injury by C5b-9, suggesting that omega-3 incorporation did not limit phospholipid (PL) hydrolysis by PLC. From this we can conclude that the protective effect of fish oil in PHN does not appear to result from the preservation of GEC integrity but is likely related to changes in the production of lipid mediators.

Characterization of a rat glomerular visceral epithelial cell line

Cultures of glomerular epithelial cells (GEC) are currently used to identify important cellular and molecular mechanisms involved in the pathogenesis of renal diseases. However, there is still controversy in the literature as to the visceral or parietal origin of cultured GEC. Our aim was to firmly establish the nature of a GEC cell line. The reactivity of cultured GEC was investigated with a large panel of mono- and polyclonal antibodies by using immunofluorescent techniques and compared with literature data on the in vivo expression of these antigens on podocytes. In addition, the podocyte specific 5A (podocalyxin), 13A and 27A (9-O-acetylated GD3) antigen expression was investigated in immuno-overlay experiments with isolated gangliosides and in immunoprecipitations with metabolically labelled cells. In general, immunoreactivities between cultured GEC and literature data on GEC in vivo expressions were similar. Important podocyte epitopes in vivo were expressed by cultured GEC such as podocalyxin, gp330 and the 13A antigen. Cultured GEC however differed from their in vivo counterparts in their expression of keratin-18, their lack of expression of pp44 and no detectable immunohistological expression of the ganglioside 9-O-acetylated GD3. Interestingly, the podocyte-specific epitope 9-O-acetylated GD3 was detected by the 27A antibodies in immuno-overlays of isolated GEC gangliosides. Moreover, by using the 27A antibody, we were able to precipitate the podocyte-specific 103-kD protein from 35S-methionine metabolically labelled GEC. From our immunohistological data together with the detectability of the 27A antigen we conclude that the cell line we use very probably originates from glomerular visceral epithelial cells.

Fish oil ameliorates renal injury and hyperlipidemia in the Milan normotensive rat model of focal glomerulosclerosis

Rats of the Milan normotensive rat strain (MNS) spontaneously develop severe proteinuria and excessive glomerular thromboxane (Tx)A2 production at a young age. These abnormalities are accompanied by podocyte alterations, progressive focal glomerulosclerosis (FGS), and interstitial fibrosis, resembling human FGS. Since it has been shown that pharmacologic Tx-synthase inhibition protects MNS rats from these changes, it was hypothesized that a fish oil (FO) enriched diet, by enhancing TxA3 production instead of TxA2, might afford similar protection, compared with diets enriched in safflower oil (SO) or lard (LD). Rats were pair-fed 11% fat diets from age of 1 to 11 months. Glomerular TxA2 at 11 months was significantly lower in PO-fed rats than in SO- and LD-fed rats (11 +/- 3.0, 69 +/- 3.0, 59 +/- 19.0 nanograms per min/mg, respectively; P < 0.001). At 3 months, urinary albumin excretion was similar among the groups. Over the course of the study, rats fed FO developed significantly less albuminuria than the SO and LD groups (P < 0.001 by analysis of variance for repeated measures), such that the values at 11 months were 25 +/- 5.8, 49 +/- 8.7, and 68 +/- 13.0 mg/24h, respectively. Serum cholesterol and triglycerides were also significantly lower in FO-fed rats than in SO- and LD-fed rats. The extent of FGS was similar in the three groups, but FO-fed rats had less interstitial injury than the other groups. It was observed that a fish-oil diet substantially alleviated albuminuria, normalized nephrotic hyperlipidemia, and reduced interstitial injury, but did not prevent the development of FGS in the MNS model.

Developmental expression of the nephritogenic antigen of monoclonal antibody 5-1-6

The biogenesis of p51, the target of nephritogenic monoclonal antibody 5-1-6, was studied in the developing glomerulus by immunolocalization and metabolic labeling. The localization of p51 was compared with that of ZO-1, a component of the cytoplasmic face of the epithelial slit diaphragm, and with that of podocalyxin, and apical marker of the podocyte. p51 first became faintly, but clearly, detectable on the basal and lateral sides of the developing podocytes at the S-shaped body stage. Staining intensity increased with further maturation and was restricted to the visceral epithelial cells. On immunoelectron microscopy, the antigen was seen along the basal and lateral surfaces below occluding junction at the early capillary loop stage and later, with the interdigitation of foot processes, became concentrated in the slit pores. At no stage was p51 seen on the apical surface. p51 and ZO-1 were closely localized in the mature glomerulus but arrived at their final positions from opposite directions. p51 was on basal and podocalyxin was on apical sides of the glomerular epithelium from the S-shaped body stage onwards. Metabolic labeling studies showed that p51 is actively synthesized during initial glomerular development and that the rate of synthesis declines substantially with maturation. We conclude that p51 is primarily synthesized during the initial glomerular development, becomes concentrated in the slit pores of mature podocytes, and serves as a basal differentiation marker for podocytes.

The effect of VH residues 6 and 23 on IgG3 cryoprecipitation and glomerular deposition

MRL/lpr mice spontaneously develop a lupus-like autoimmune syndrome characterized by immunopathologic manifestations such as necrotizing vasculitis of the skin and glomerulonephritis. A feature of this autoimmune syndrome is the production of extremely large amounts of monoclonal IgG3 cryoglobulins. The structural basis of IgG3 cryoprecipitation is not well understood. Although the IgG3 isotype is necessary for cryoprecipitation, not all IgG3 antibodies cryoprecipitate. It has been postulated that electrostatic charge may be influential in cryoprecipitation. To investigate this problem, the VH and VL sequences of a panel of IgG3 cryoglobulins and non-cryoglobulins were compared, with particular attention to charged amino acid differences. At VH residues 6 and 23 the cryoglobulins were more positively charged than their non-cryoglobulin counterparts. To analyze further the effect of charge on cryoprecipitation, the sequence of an IgG3 monoclonal cryoprecipitating rheumatoid factor was modified by site-directed mutagenesis. The more positive residues at VH 6 and 23 present in some of the cryoglobulin antibodies were mutated to the more negative residues found in the non-cryoglobulins. The results show that VH residue 6 affects cryoprecipitation while residue 23 does not. When injected into normal BALB/c mice, the unmutated antibody produced glomerular immune deposits and focal glomerulonephritis, whereas loss of cryoprecipitability by mutating residue 6 completely abrogated glomerular immune deposition and glomerular injury. In contrast, the mutation at residue 23 which retains cryoprecipitability reduced glomerular immune deposition and prevented glomerular injury.

The nephritogenic immune response

The past year has witnessed continued advances along several fronts in understanding the initiation and effects of a nephritogenic immune response. New information on the major histocompatibility complex in autoimmunity suggests that major histocompatibility complex class I and class II expression is important in the initiation of the immune response. The complex pathways involved in the regulation of leukocyte recruitment in inflammation continue to unravel and the role of cytokines in these processes is being defined. The ability of antibodies directed against leukocyte adhesion molecules to attenuate inflammation in experimental glomerulonephritis opens up the possibility of new therapeutic agents for human disease. The need to reexamine the role of complement as an effector in immune renal disease is suggested by evidence of intrinsic renal complement component production. Recent information on the pathogenesis of renal scarring in crescentic glomerulonephritis suggests the importance of leukocyte-endothelial cell interaction and of delayed-type hypersensitivity in this process. The ability of the growth factors transforming growth factor-beta and platelet-derived growth factor to induce glomerulosclerosis has been documented in an innovative study using selective renal gene transfer. Finally, the potential importance of apoptosis of inflammatory cells as a mechanism limiting injury is a new focus of attention.

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

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

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

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

Management of glomerular diseases of primary and secondary origin

Most recent information on the management of glomerular diseases is clustered in three areas. In nephrotic syndrome, interest has focused on the use of cyclosporine in steroid-resistant patients, treatment of progressive membranous nephropathy with alkylating agents, and symptomatic management of unresponsive cases with angiotensin-converting enzyme inhibitors. The most recent data on lupus nephritis establish the efficacy of intravenous cyclophosphamide in the long-term preservation of renal function and the lack of benefit of plasmapheresis in patients with severe disease. In rapidly progressive glomerulonephritis, the discovery of circulating antibodies to neutrophil cytoplasmic antigens has proved valuable in diagnosing certain forms of renal vasculitis. A rational approach to treating such patients is beginning to crystallize.

Quantification of glomerular epithelial cell adhesion by using anti-DNA antibodies in ELISA

A sensitive and reproducible microassay is described for quantification of adhesion of cells to matrix-coated 96-wells plates under different experimental conditions. For this purpose glomerular visceral epithelial cells (GVEC) were used. Attached GVEC were fixed with methanol and incubated with a monoclonal anti-DNA antibody. Following standard procedures, the amount of bound antibody was quantified by ELISA. A positive linear relationship in the range of 800-5000 cells per well was found between OD values and cell numbers obtained by hand-counting (r = 0.94, p less than 0.001). The assay is 10 to 100 times more sensitive than most other adhesion assays. The applicability of the ELISA assay was demonstrated by manipulation of the temperature during adhesion and by using different concentrations of the matrix-molecules fibronectin, EHS-laminin and collagen type I. The ELISA assay was found to be unaffected by non-specific interaction of anti-DNA antibodies with the matrix molecules used for coating. The assay was neither affected by potential release of DNA from the GVEC under these different experimental conditions. In conclusion, this cell adhesion microassay is simple, reliable, sensitive, and cost-effective, since it requires small amounts of GVEC and reagents.

Nephrotoxic antiserum identifies a beta 1-integrin on rat glomerular epithelial cells

A postulated mechanism of immune glomerular injury is a direct interaction between antibody and glomerular epithelial cell (GEC) surface antigens. To explore this hypothesis, we examined the interaction of the noncomplement-fixing gamma 2-subclass of sheep anti-rat nephrotoxic serum (NTS), which causes immediate complement- and neutrophil-independent proteinuria in vivo, with rat GECs in culture. Reactivity of NTS with GEC surface antigens was determined by positive immunofluorescence of GEC plasma membranes and by the ability of NTS-coated tissue culture wells to provide an adhesive substrate for GECs. NTS immunoprecipitated two proteins (135 and 118 kDa) from surface-labeled GECs. Proteins of similar molecular mass were precipitated by a polyclonal rabbit antibody that identifies the beta 1-integrin chain of the mouse fibronectin receptor (anti-FnR). In addition, NTS identified similarly sized bands on Western blot analysis of cell membranes from isolated rat glomeruli. Similar reactivity was eluted from the glomeruli of proteinuric rats injected with NTS. NTS significantly inhibited GEC adhesion to laminin, types I and IV collagen, and fibronectin and prevented GEC spreading on types I and IV collagen. Anti-FnR similarly inhibited GEC adhesion. Cell viability was not affected. These results show that NTS recognizes a pair of GEC surface proteins that have the characteristics of an alpha- and beta 1-integrin and, at low concentrations, disrupt cell-matrix interactions.

Production and polarized secretion of basement membrane components by glomerular epithelial cells

To study the formation of basement membrane by glomerular epithelial cells (GECs), production and secretion of type IV collagen and laminin by rat GECs in culture were evaluated. GECs produced two chains of type IV collagen (180 and 170 kDa) in the ratio of approximately 2 to 1, when immunoprecipitated with antibody to type IV collagen of mouse Engelbreth-Holm-Swarm (EHS) sarcoma. GECs also produced proteins that were precipitated by antibody to EHS laminin, i.e., two bands each in the positions of the A and B chains of mouse laminin. On enzyme-linked immunosorbent assay (ELISA), type IV collagen and laminin were found mainly in the cell-associated fraction and in the subepithelial culture medium. Confluent GECs on membrane filters formed a tight barrier against the flux of macromolecules. Under these conditions, 80% of newly synthesized and secreted matrix proteins were detected in the basolateral medium. Moreover, treatment with ammonium chloride, which is known to affect polarized secretion, caused both type IV collagen and laminin to be secreted via the basolateral and apical surfaces in similar amounts. These results indicate that cultured GECs are polarized and that they produce and secrete basement membrane components via the basolateral side.

Effect of nephritogenic antibody on complement regulation in cultured rat glomerular epithelial cells

In passive Heymann nephritis, a rat model of membranous nephropathy, antibody (anti-Fx1A) activates C on the surface of the glomerular epithelial cell (GEC), leading to GEC injury and proteinuria. In this study, we examined C activation by anti-Fx1A in cultured rat GEC. In addition to anti-Fx1A IgG, anti-Fx1A F(ab')2 and Fab' led to GEC injury in the presence of rat or human sera as sources of C. Cytotoxicity was Mg2+ and factor B dependent, but Ca2+ independent, indicating that anti-Fx1A activated the C alternative pathway (AP). Furthermore, in the presence of Mg2+ and factor B, anti-Fx1A enhanced 125I-C3b deposition on GEC in the absence of classical pathway activation. AP C3 and C5 convertases formed on GEC (GEC-C3bBbP) were inactivated over time, probably due to binding of GEC C regulatory proteins. This inactivation was prevented when GEC-C3bBbP were incubated with anti-Fx1A IgG. An antibody raised against cultured GEC that binds to GEC in vitro and in vivo had no effect on C3 and C5 convertases, suggesting that stabilization of C3bBbP is unique to anti-Fx1A. Anti-Fx1A Fab' also stabilized GEC-C3bBbP, indicating that cross-linking of membrane Ag was not required. C3bBbP on E were not affected by anti-Fx1A, excluding direct stabilization of convertases by anti-Fx1A. Therefore, anti-Fx1A inhibits C regulation on GEC, which can account for its ability to activate the AP. This represents a potentially powerful mechanism of producing disease in vivo.

Effect of nephritogenic antibody on complement regulation in cultured rat glomerular epithelial cells

In passive Heymann nephritis, a rat model of membranous nephropathy, antibody (anti-Fx1A) activates C on the surface of the glomerular epithelial cell (GEC), leading to GEC injury and proteinuria. In this study, we examined C activation by anti-Fx1A in cultured rat GEC. In addition to anti-Fx1A IgG, anti-Fx1A F(ab')2 and Fab' led to GEC injury in the presence of rat or human sera as sources of C. Cytotoxicity was Mg2+ and factor B dependent, but Ca2+ independent, indicating that anti-Fx1A activated the C alternative pathway (AP). Furthermore, in the presence of Mg2+ and factor B, anti-Fx1A enhanced 125I-C3b deposition on GEC in the absence of classical pathway activation. AP C3 and C5 convertases formed on GEC (GEC-C3bBbP) were inactivated over time, probably due to binding of GEC C regulatory proteins. This inactivation was prevented when GEC-C3bBbP were incubated with anti-Fx1A IgG. An antibody raised against cultured GEC that binds to GEC in vitro and in vivo had no effect on C3 and C5 convertases, suggesting that stabilization of C3bBbP is unique to anti-Fx1A. Anti-Fx1A Fab' also stabilized GEC-C3bBbP, indicating that cross-linking of membrane Ag was not required. C3bBbP on E were not affected by anti-Fx1A, excluding direct stabilization of convertases by anti-Fx1A. Therefore, anti-Fx1A inhibits C regulation on GEC, which can account for its ability to activate the AP. This represents a potentially powerful mechanism of producing disease in vivo.

Cytosolic calcium and protein kinase C reduce complement-mediated glomerular epithelial injury

In rat membranous nephropathy, protein-uria is due to formation of the C5b-9 membrane attack complex of complement (C), and is associated with morphological evidence of glomerular epithelial cell (GEC) injury. Analogous morphological changes are induced by C5b-9 in cultured GEC. In addition, in cultured GEC C5b-9 induces Ca2+ influx, as well as Ca2+ mobilization and increased 1,2-diacylglycerol due to the activation of phospholipase C. In this study we investigated how this GEC activation pattern might influence C-mediated GEC injury. We demonstrate that the C5b-9-induced increase in cytosolic Ca2+ concentration ([Ca2+]i) did not impair ATP generation by mitochondria, suggesting that it does not contribute to cytotoxicity. Moreover, this increase in [Ca2+]i protected GEC from C-mediated cytolysis. However, a large increase in [Ca2+]i (produced by the Ca2+ ionophore A23187) impaired ATP generation and aggravated C-mediated cytotoxicity, suggesting that intact mitochondrial activity is necessary for GEC to withstand C attack. Activation of protein kinase C (PKC) by phorbol myristate acetate (PMA) also decreased C-mediated cytolysis. Conversely, C lysis was enhanced in GEC that had been pretreated for 18 hours with a high dose of PMA to deplete PKC, and following PKC inhibition with H-7. Therefore, PKC activation, possibly resulting from C5b-9-induced increase in 1,2-diacylglycerol, triggered mechanisms that protected GEC from C-mediated injury. Thus, as a consequence of C5b-9-induced phospholipase activation, the amount of C-induced GEC injury is diminished.

Extracellular matrix regulates proliferation and phospholipid turnover in glomerular epithelial cells

To understand how glomerular epithelial cell (GEC) growth might be regulated in health and disease, we studied the effects of growth factors and extracellular matrix on proliferation and membrane phospholipid turnover in cultured rat GECs. In GECs adherent to type I collagen matrix, epidermal growth factor (EGF), insulin, and serum stimulated DNA synthesis and increased cell number. In addition, GECs proliferated when adherent to type IV collagen, but not to laminin or plastic substrata. Attachment of GECs to the substrata that facilitated proliferation (types I or IV collagen) produced increases in 1,2-diacylglycerol (DAG), an activator of protein kinase C (PKC). Increased DAG was associated with hydrolysis of inositol phospholipids and an increase in inositol trisphosphate and was not dependent on the presence of growth factors. After PKC downregulation (by preincubation with a high dose of phorbol myristate acetate), DNA synthesis was enhanced in GECs adherent to collagen. Thus contact of GECs with collagen matrices is required for serum, EGF, or insulin to induce proliferation. Collagen matrix also activates phospholipase C. As a result, the DAG-PKC signaling pathway desensitizes GECs to the mitogenic effects of growth factors and might promote cell differentiation. Understanding the interaction between GECs, growth factors, and extracellular matrix may elucidate the mechanisms of proliferation during glomerular injury.

Loss and rearrangement of glomerular basement membrane laminin during acute nephrotoxic nephritis in the rat

Many earlier studies have shown that the intravenous injection into rats of sheep antibodies against rat glomerular basement membrane (GBM) induces a rapid influx of neutrophils and proteinuria (nephrotoxic nephritis or NTN). The GBM antigens recognized by nephrotoxic antibodies (NTAbs) have not been identified conclusively. Our experiments presented here, however, showed that NTAbs did not significantly reduce binding of anti-laminin IgGs to laminin-coated enzyme-linked immunosorbent assay (ELISA) plates or to the GBM in vivo, indicating little cross-reactivity between the NTAbs and laminin. To evaluate possible changes in GBM architecture during acute stages of NTN, the ultrastructural distribution of laminin was determined by postfixation, postembedding immunogold labeling, and compared between normal and nephritic rats. The density of immunoreactive GBM laminin was significantly reduced in rats with acute NTN. In addition, conjugates of anti-laminin IgG and horseradish peroxidase were intravenously injected into rats that then received injections of NTAbs. Anti-laminin peroxidase conjugates were also injected after administering NTAbs. In both cases, an overall decrease in anti-laminin peroxidase reaction product was observed as compared to normal controls. The densest labeling was seen in the lamina rara interna, especially in areas of endothelial cell detachment. Some immunoperoxidase reaction product was also bound to basal surfaces of detaching endothelial cells, demonstrating the removal of at least some laminin from the GBM. A decrease in GBM binding of intravenously injected anti-laminin IgG, both before and after injection of rats with NTAbs, was also confirmed by postembedding immunogold labeling. Furthermore, morphometry showed that the GBM was significantly wider in nephritic rats than in controls, indicating a redistribution of laminin over a greatly increased area. These immunoultrastructural findings show, therefore, that GBM architecture is altered in the early phase of NTN.

Complement C5b-9 complex activates phospholipases in glomerular epithelial cells

In rat membranous nephropathy, formation of the C5b-9 membrane attack complex (MAC) leads to proteinuria in association with glomerular visceral epithelial cell (GEC) injury. These alterations in GEC function and morphology might result from changes in intracellular free Ca2+ concentration [( Ca2+]i) and activation of phospholipases. We demonstrate that in cultured rat GEC, antibody-directed formation of noncytolytic amounts of the MAC induced a rapid and sustained increase in [Ca2+]i that was partly inhibited by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The MAC elevated levels of inositol bis- (IP2) and trisphosphate (IP3), as well as 1,2-diacylglycerol (DAG) and phosphatidic acid (PA). In permeabilized GEC, IP3 released Ca2+ from intracellular stores. Cellular 45Ca2+ uptake was also increased by the MAC. Thus, in GEC, the MAC induced Ca2+ mobilization from intracellular stores secondary to activation of phospholipase C and production of IP3, as well as enhanced Ca2+ influx. In addition, C5b-9 stimulated release of arachidonic acid (AA), prostaglandin F2 alpha, and thromboxane A2. Indomethacin partially inhibited the increase in DAG levels observed with the MAC, whereas the prostaglandin H2/thromboxane A2 analogue U46619 elevated DAG, suggesting that an eicosanoid product of MAC-induced AA release may enhance the activation of phospholipase C. Activation of phospholipases by the MAC may lead to altered GEC function and thereby contribute to the pathophysiological changes that characterize complement-dependent rat membranous nephropathy.

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

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

Decay accelerating factor regulates complement activation on glomerular epithelial cells

Epithelial cells of the glomerular capillary are the site of C5b-9 mediated injury in rat membranous nephropathy. We investigated the regulation of C activation by cultured glomerular epithelial cells (GEC). Rat and human GEC were more resistant to C injury by homologous C than heterologous C. In human GEC homologous C cytotoxicity was enhanced by antiserum to decay accelerating factor (DAF) indicating that homologous C activation was, at least in part, restricted by membrane DAF. Anti-DAF immunoprecipitated a 67-kDa protein from human glomeruli. In rat GEC, pronase and phosphatidylinositol-specific phospholipase C (which are known to inactivate human DAF) enhanced cytotoxicity by homologous C. Thus, DAF is present on human GEC in culture and in human kidney glomeruli, and a DAF-like protein is present on cultured rat GEC. These proteins regulate C activation in vitro and may play a role in controlling C activation on GEC in vivo.

Decay accelerating factor regulates complement activation on glomerular epithelial cells

Epithelial cells of the glomerular capillary are the site of C5b-9 mediated injury in rat membranous nephropathy. We investigated the regulation of C activation by cultured glomerular epithelial cells (GEC). Rat and human GEC were more resistant to C injury by homologous C than heterologous C. In human GEC homologous C cytotoxicity was enhanced by antiserum to decay accelerating factor (DAF) indicating that homologous C activation was, at least in part, restricted by membrane DAF. Anti-DAF immunoprecipitated a 67-kDa protein from human glomeruli. In rat GEC, pronase and phosphatidylinositol-specific phospholipase C (which are known to inactivate human DAF) enhanced cytotoxicity by homologous C. Thus, DAF is present on human GEC in culture and in human kidney glomeruli, and a DAF-like protein is present on cultured rat GEC. These proteins regulate C activation in vitro and may play a role in controlling C activation on GEC in vivo.