Epitope specific induction of proteinuria by monoclonal antibodies

Antibody induced injury to podocytes with proteinuria and foot process swelling in a transgenic (T16) mouse

T16 mice contain a human 3' untranslated sequence of the Thy 1.1 gene. Unlike normal mice they express Thy 1.1 protein on the podocytes which was immuno-localized to podocyte apical and basal plasma membranes and filtration slit. When monoclonal anti-Thy 1.1 antibody (OX7) was injected in nonproteinuric heterozygous mice there was rapid podocyte foot process swelling and proteinuria. Immunofluorescence showed granular glomerular OX7 binding at one hour. Progressive loss of pedicels occurred with 17.9 +/- 2.5, 14.4 +/- 1.1 and 10.5 +/- 3.5 per 10 nm glomerular basement membrane (GBM) remaining 1, 6 and 24 hours, respectively, after 1 mg OX7, vs 32.2 +/- 2.0 in T16 mice given saline. Twenty-four hour proteinuria was OX7 dose-dependent, peaked at 1-3 days and reduced to near basal levels 9-11 days thereafter. Proteinuria was nonselective except at very low doses (0.1 mg OX7) where microalbuminuria was seen. F(ab')2 OX7 administration also caused proteinuria in T16 mice. One milligram F(ab')1 OX7 caused diffuse foot process swelling without manifest proteinuria in T16 mice. Anti-Thy 1.1 IgM monoclonal antibody did not produce the effects of OX7 in T16 mice. Foot process swelling was not modified by histamine or 5-hydroxytryptamine antagonists. OX7 did not cause complement activation or leucocyte infiltration, hence glomerular injury appeared to be mediated directly by the antibody.

Active Heymann nephritis in complement component C6 deficient rats

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

Effect of traditional Chinese medicine (sairei-to) on monoclonal antibody-induced proteinuria in rats

The effects of traditional Chinese medicine (Sairei-to) on monoclonal antibody (mAb) inducing proteinuria were examined. Four hundred, 200 and 100 mg/kg body weight (BW) of Sairei-to and phosphate-buffered saline (PBS) as a control were injected intraperitoneally into four groups of female Wistar rats every day from 5 days before intravenous injection of mAb to the end of the experimental period. The amount of urinary protein excretion was significantly suppressed in roughly a dose-dependent manner. For example, 116.6 +/- 89.7 mg/day of proteinuria was observed in control groups compared to 4.2 +/- 15.2 mg/day in the 400 mg/kg BW of Sairei-to treated group 2 days after mAb injection (P < 0.01). Statistically significant (P < 0.01) differences were again observed in a repeat experiment (122.1 +/- 53.7 vs 10.2 +/- 10.1 mg/day on the 2nd day) without affecting the glomerular filtration rate. No significant difference was recognized between the total amount of mAb bound to glomeruli 1 h after mAb injection in Sairei-to-treated and non-treated rats, indicating that Sairei-to pretreatment has no effects on the number or quality of antigenic molecules. The effect of Sairei-to on a non-immunological model of proteinuria was also examined. No significant reduction of proteinuria by similar Sairei-to treatment was observed in aminonucleoside of puromycin nephropathy. The authors conclude that mAb-induced proteinuria in rats is significantly suppressed by the traditional Chinese medicine, Sairei-to.

Mechanisms of proteinuria in noninflammatory glomerular diseases

Neither the initiating factors nor the proximate causes of injury that produce proteinuria in nephrotic syndrome have been clearly defined. Immune mechanisms have been postulated in minimal-change nephrotic syndrome (MCNS), focal segmental glomerular sclerosis (FSGS), and glomerular sclerosis associated with human immunodeficiency virus (HIV) infection. Circulating factors have been proposed in MCNS and FSGS, although no specific mediator has been identified. Prompt remission of proteinuria following steroid treatment and the presence of altered immune responsiveness in patients with MCNS have been used to support the participation of an immune mechanism in the pathogenesis of MCNS. Both FSGS and HIV-related nephropathy are usually steroid-resistant. Immune mechanisms are postulated in FSGS because of early recurrence after transplantation, and in HIV-related nephropathy because of the numerous associated immune abnormalities. Experimental models of nephrotic syndrome based on neutralization of glomerular charge, toxic injury to podocytes, injection of antibodies to glomerular components, or abnormalities in transgenic mice have been used to define mechanisms of glomerular injury. This review summarizes physiologic and immunologic abnormalities in MCNS, FSGS, and HIV-associated nephropathy and in several experimental models of nephrotic syndrome, and outlines the immunologic mechanisms and cellular reactions that may be responsible for glomerular dysfunction in these entities.

Rat intestinal M cells contain acidic endosomal-lysosomal compartments and express class II major histocompatibility complex determinants

BACKGROUND

It is generally believed that M cells do not modify the antigens they transport from the intestinal lumen to underlying immunocompetent cells because it has been reported that M cells contain few elements of the lysosomal system.

METHODS

We used specific cytochemical and immunocytochemical probes to examine whether M cells in jejunal Peyer's patches of adult rats contain the requisite intracellular components to process and potentially present endocytosed antigens.

RESULTS

M cells contained acid phosphatase-enriched prelysosomelike and lysosomelike structures. A basic congener of dinitrophenol, which concentrates in acidic cell compartments, is localized following its instillation into Peyer's patch-containing ligated jejunal loops to the endosomal-lysosomal system of M cells. Prelysosomelike and lysosomelike structures in ultrathin cryosections of M cells reacted with polyclonal antibody to a membrane glycoprotein (lgp120) enriched in prelysosomes and lysosomes. Using monoclonal antibody OX6 as a probe, M cells expressed the major histocompatibility complex (MHC) class II determinant, Ia, on the basolateral plasma membrane and in organelles with structural features of endosomes, prelysosomes, and lysosomes. Expression was enhanced by pretreatment with interferon gamma.

CONCLUSIONS

M cells possess acidic endosomal and acid phosphatase-containing prelysosomal and lysosomal compartments and express MHC class II determinants. Hence, M cells may have the capacity to process and present endocytosed antigens to adjacent intraepithelial T lymphocytes.

Immune modulation of biologic systems in renal somatic cells

The various theories discussed here suggest that somatic renal cells are susceptible to biologic modulation by the immune system independent of an inflammatory effect. (1) The mode of repression of type IV collagen synthesis by novel, soluble antigen-binding proteins, the down-regulation of class II MHC expression with interruption of antigen presentation to epithelia after selective gene regulation by antibody, and the diverse interactions of antibody with renal glomerular cells producing functional disturbances in endocytosis and permselectivity; (2) modification of surface-antigen composition; (3) alteration of matrix deposition, remodeling and composition; (4) biophysical perturbation of cytoskeletal and cell membrane components; (5) and lastly, alterations in cell adhesion through cell-surface alterations, all lend testimony to the richness of the signal transduction pathways in somatic cells. Although the preceding examples represent only a small fraction of those which may take place within the glomerular and tubular microenvironments, these paradigms may nevertheless serve as new models upon which one can consider the multitude of potential communications between disparate biologic systems that connect in complex organisms.

Epitope-specific induction of mesangial lesions with proteinuria by a MoAb against mesangial cell surface antigen

A MoAb 1-22-3 (IgG3) was produced in mice immunized with rat glomeruli. A blotting study indicated the antigen molecule recognized by this MoAb has a molecular weight of about 25 kD, which is the same as that of the Thy 1.1 molecule. This MoAb is capable of inducing the morphological changes similar to those induced by anti-thymocyte serum or the anti-Thy 1.1 MoAb, ER4 and massive proteinuria in rats by a single i.v. injection. Proteinuria started immediately after MoAb 1-22-3 injection and peaked on day 5. Reaction products were detected by immunoelectron microscopy in vitro on the limited mesangial cell surface facing endothelial cells and in vivo in partially lysed mesangial cells 30 min after injection. Unlike the proteinuria-inducing MoAb ER4, reactivity of MoAb 1-22-3 was detected neither on endothelial cells, epithelial cells, nor along the glomerular basement membrane in vivo and in vitro. There is a difference in reactivity toward guinea-pig and rabbit materials between MoAb 1-22-3 and the commercial anti-Thy 1.1 MoAb (OX7). The antigenic determinant of MoAb 1-22-3 is concluded to be a new epitope and only the binding of MoAb 1-22-3 to this epitope proved to lead to an abnormal increase of glomerular capillary wall permeability.

Quantitative studies of monoclonal antibody 5-1-6-induced proteinuric state in rats

Murine monoclonal antibody (MoAb) 5-1-6 was already reported to bind to epithelial cell foot processes and to cause proteinuria in rats. In vivo kinetics of the injected MoAb 5-1-6, relationship between the quantity of kidney-binding antibody and proteinuria, and changes in the amount of antigenic molecule recognized by this MoAb in the proteinuric state were studied. The amount of total kidney-binding antibody (TKAb) as determined 1 h after a 2 mg administration was 50.8 +/- 10.4 micrograms/2 kidneys, and TKAb declined to 1.9 +/- 0.4 at day 15. The minimum dose of MoAb required to induce proteinuria was 125 micrograms as the injected dose. This dose corresponded to 12.8 micrograms of TKAb at 1 h and 0.34 micrograms of TKAb at day 5. The amount of MoAb 5-1-6 binding to isolated normal glomeruli was also shown to exceed 147.7 micrograms/76,000 glomeruli, indicating proteinuria to be induced provided more than 8.7% (= 12.8/147.7) of the critical epitopes is specifically occupied by MoAb. The total amount of MoAb 5-1-6 bound to glomeruli in vivo and in vitro was assayed with [125I]-labelled anti-mouse IgG. The amount of [125I] anti-mouse IgG bound to glomeruli was 6.93 +/- 0.45 micrograms/10,000 glomeruli from rat 5 days after this MoAb injection and 26.58 +/- 0.66 micrograms/10,000 control glomeruli, indicating the decrease in the number of MoAb 5-1-6-recognized antigen molecules in glomeruli isolated from the rat in proteinuric state induced by this MoAb. Thus, the MoAb 5-1-6-recognized molecule itself may principally function to regulate the permeability of the glomerular capillary wall and the decrease of the molecule may lead to proteinuria.

Antigen processing and presentation by glomerular visceral epithelium in vitro

Although macrophages are considered the prototype of antigen presenting cells (APC), recent studies have emphasized the potential role of several parenchymal and mesenchymal cells in this process. We have studied the capacity of cultured glomerular visceral epithelial cells (GEC) to act as effective APC and compared this capacity with that demonstrated by peritoneal macrophages. Affinity-purified and in vitro propagated rat GEC were exposed to hen egg lysozyme, keyhole limpet hemocyanin, and cationic ferritin. As effector cells, we used antigen-specific T cell hybridomas; the level of antigen presentation was assessed by determining the level of interleukin 2 (IL-2) present in tissue culture supernatants. Cytokine-treated GEC were capable of processing and presenting all antigens in a dose-dependent manner. Crucial for antigen presentation were intracellular processing of antigen and the presence of Ia on the cell surface. Our findings indicate that GEC can act as effective APC, and further suggest that this capacity may be relevant to cell-mediated immune injury at the level of the glomerular capillaries in vivo.

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.

Heymann antigen GP330 demonstrates affinity for fibronectin, laminin, and type I collagen and mediates rat proximal tubule epithelial cell adherence to such matrices in vitro

We have utilized monoclonal antibodies directed against glycoproteins on the surface of proximal tubule epithelial cells (PTEC) to study their interaction with matrix components. PTEC exposed to monoclonal antibodies directed against a 330-kDa cell surface glycoprotein exhibited a significant epitope-specific inhibition of attachment and proliferation on type I collagen-, fibronectin-, laminin-, and gelatin-coated tissue culture surfaces. This effect was not due to antibody toxicity since such cells did not exhibit metabolic dysfunction in suspension cultures and the inhibition could be reversed upon removal of the antibody from the cell surface. Furthermore, detergent-solubilized gp330 demonstrated specific affinity for fibronectin, laminin, and type I collagen which was not inhibited by Arg-Gly-Asp-containing peptides. A monoclonal antibody directed against the receptor epitope was capable of promoting PTEC adherence and growth when such an antibody was immobilized on cell culture dishes. Although gp330 acted as a receptor for matrix proteins in primary cultures of freshly isolated PTEC, this effect was not demonstrable in established cultures. These results suggest that freshly isolated PTEC depend on gp330 for their attachment to matrix molecules while in vitro-adapted PTEC rely on other receptors activated by culture conditions. The affinity of gp330 for matrix molecules may be of pathogenic relevance in the persistence of gp330-containing immune complexes formed in the glomerular capillary wall in experimental membranous nephropathy (Heymann nephritis).

Expression of enzymatically active rat dipeptidyl peptidase IV in Chinese hamster ovary cells after transfection

Dipeptidyl peptidase IV (DPPIV) is a cell surface membrane glycoprotein expressed in many tissues. We have subcloned the coding region of a full-length cDNA for DPPIV into the inducible eukaryotic expression vector pMSG. The resulting construct was used to transfect Chinese hamster ovary (CHO) cells. Stable transformants were found to express DPPIV, and the expression is enhanced by dexamethasone. Metabolic labeling of the transfected cells with [35S]Met followed by immunoprecipitation revealed the presence of two specific products of apparent Mr 100,000 (100-kDa form) and 110,000 (110-kDa form), respectively. Pulse-chase experiments demonstrated that the 100-kDa form can be chased into the 110-kDa form, suggesting the 100-kDa form is the precursor of the 110-kDa form. Further studies with endo H treatment demonstrated that the carbohydrate structures are of the high-mannose type, and of the complex type for the 100- and 110-kDa forms, respectively. The 110-kDa form is present at the cell surface as shown by its accessibility to cell surface iodination. The DPPIV expressed on the cell surface is resistant to digestion by relatively high concentrations of trypsin. Studies also demonstrated that the surface DPPIV is fairly stable with a half-life for turnover of about 40 h. Furthermore, the DPPIV produced in the transfected cells displays specific dipeptidyl peptidase activity. The stably transfected cells that express enzymatically active DPPIV in an inducible manner will provide an excellent system for further biochemical, functional, and cell biological characterizations of DPPIV.

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

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

Expression of dipeptidyl peptidase IV in rat tissues is mainly regulated at the mRNA levels

Dipeptidyl peptidase IV (DPPIV) is a serine peptidase that cleaves N-terminal dipeptides from polypeptides when the second residue is a proline or an alanine. We have recently cloned cDNAs for rat gp110, a membrane glycoprotein with Mr of 110,000 isolated initially from rat liver. Studies reported here establish that the gp110 for which we have cloned cDNAs is DPPIV. Using the antibodies against and cDNA for DPPIV, we have assessed the tissue distribution of DPPIV by molecular approaches. Immunoblot analysis demonstrated that DPPIV is present in the kidney, lung, and small intestine at high levels, in the liver and spleen at moderate levels, and in the heart at low levels. The highest levels of mRNA for DPPIV were detected in the kidney and small intestine as compared to moderate levels found in the lung, liver, and spleen. The lowest levels of DPPIV mRNA were found in the stomach, testis, and heart. No detectable DPPIV protein and mRNA were found in brain or muscle. LDPPIV protein and mRNA are present at much lower levels in fetal livers as compared to the adult liver. Indirect immunofluorescence microscopy demonstrated that DPPIV is localized in the bile canaliculus of hematocytes and in the apical membrane domains of kidney tubule and small intestine. Further studies by Southern blot analysis indicate that DPPIV is encoded by a single gene.