Immune-mediated injury to basement membranes in mice immunized with murine laminin

Basement membranes and autoimmune diseases

Basement membrane components are targets of autoimmune attack in diverse diseases that destroy kidneys, lungs, skin, mucous membranes, joints, and other organs in man. Epitopes on collagen and laminin, in particular, are targeted by autoantibodies and T cells in anti-glomerular basement membrane glomerulonephritis, Goodpasture's disease, rheumatoid arthritis, post-lung transplant bronchiolitis obliterans syndrome, and multiple autoimmune dermatoses. This review examines major diseases linked to basement membrane autoreactivity, with a focus on investigations in patients and animal models that advance our understanding of disease pathogenesis. Autoimmunity to glomerular basement membrane type IV is discussed in depth as a prototypic organ-specific autoimmune disease yielding novel insights into the complexity of anti-basement membrane immunity and the roles of genetic and environmental susceptibility.

Autoimmunity against laminins

Laminins are ubiquitous constituents of the basement membranes with major architectural and functional role as supported by the fact that absence or mutations of laminins lead to either lethal or severely impairing phenotypes. Besides genetic defects, laminins are involved in a wide range of human diseases including cancer, infections, and inflammatory diseases, as well as autoimmune disorders. A growing body of evidence implicates several laminin chains as autoantigens in blistering skin diseases, collagenoses, vasculitis, or post-infectious autoimmunity. The current paper reviews the existing knowledge on autoimmunity against laminins referring to both experimental and clinical data, and on therapeutic implications of anti-laminin antibodies. Further investigation of relevant laminin epitopes in pathogenic autoimmunity would facilitate the development of appropriate diagnostic tools for thorough characterization of patients' antibody specificities and should decisively contribute to designing more specific therapeutic interventions.

Ex vivo pathogenicity of anti-laminin γ1 autoantibodies

Autoimmunity against laminins has been described in several autoimmune diseases (including mucous membrane pemphigoid, anti-laminin γ1 pemphigoid, and connective tissue diseases), in pregnancy loss, and in infections such as Chagas disease. Except for anti-laminin-332 mucous membrane pemphigoid, adequate evidence has been lacking for the tissue injury potential of laminin-specific antibodies and the pathogenic epitopes. We evaluated the pathogenic potential of antibodies targeting laminin γ1, a major constituent of basement membranes and the main antigen in anti-laminin γ1 pemphigoid. Rabbit antibodies were generated against fragments of the N-terminus and C-terminus of murine laminin γ1, and their ability to disrupt ligand interactions and/or to activate complement and granulocytes was assessed using previously established ex vivo assays. Our findings document a pathogenic potential of antibodies targeting the laminin γ1 N-terminus. These antibodies interfere with the binding of nidogen to laminin and can activate granulocytes and the complement cascade. We detected antibodies with different degrees of reactivity with laminin γ1 N-terminus in patients with anti-laminin γ1 pemphigoid, cutaneous lupus erythematosus, and scleroderma. Our results provide mechanistic insights into the tissue damage associated with laminin autoimmunity and could facilitate development of appropriate diagnostic tools and therapeutic strategies.

Humoral autoimmunity to basement membrane antigens is regulated in C57BL/6 and MRL/MpJ mice transgenic for anti-laminin Ig receptors

Basement membrane proteins are targeted in organ-limited and systemic autoimmune nephritis, yet little is known about the origin or regulation of immunity to these complex extracellular matrices. We used mice transgenic for a nephrotropic systemic lupus erythematosus (SLE) Ig H chain to test the hypothesis that humoral immunity to basement membrane is actively regulated. The LamH-Cmu Ig H chain transgene combines with diverse L chains to produce nephrotropic Ig reactive with murine laminin alpha1. To determine the fate of transgene-bearing B cells in vivo, transgenic mice were outcrossed onto nonautoimmune B6 and SLE-prone MRL backgrounds and exposed to potent mitogen or Ag in adjuvant. In this work we demonstrate that transgenic autoantibodies are absent in serum from M6 and M29 lineage transgenic mice and transgenic B cells hypoproliferate and fail to increase Ig production upon exposure to endotoxin or when subjected to B cell receptor cross-linking. Administration of LPS or immunization with autologous or heterologous laminin, maneuvers that induce nonoverlapping endogenous anti-laminin IgG responses, fails to induce a transgenic anti-laminin response. The marked reduction in splenic B cell number suggests that selected LamH-Cmu H chain and endogenous L chain combinations generate autospecificities that lead to B cell deletion. It thus appears that SLE-like anti-laminin B cells have access to and engage a tolerizing self-Ag in vivo. Failure to induce autoimmunity by global perturbations in immune regulation introduced by the MRL autoimmune background and exposure to potent environmental challenge suggests that humoral immunity to nephritogenic basement membrane epitopes targeted in systemic autoimmunity is tightly regulated.

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.

Susceptibility for infection-related glomerulopathy depends on non-MHC genes

BALB/c mice infected with Trypanosoma brucei and treated seven days after inoculation with Diminazene aceturate develop polyclonal B-cell stimulation, including production of antibodies to known nephritogenic autoantigens and glomerular disease associated with severe albuminuria. To investigate if the susceptibility for glomerular disease in this model is linked to MHC or non-MHC genes, we studied this disease in six mouse strains that were partly congenic for their MHC and partly congenic for their non-MHC genes. The course of the infection was measured by parasitemia and related to (auto)antibody production, proteinuria and glomerular deposition of immunoglobulins. The mouse strains could be divided into two groups. The first group consisted of the C57BL/6 (H-2b), C57BL/10 (H-2b) and B10.D2 (H-2d) strains, which proved to be relatively resistant to infection with Trypanosoma brucei (that is, spontaneous survival > 25 days). In sera of these mice antibodies to a broad range of antigens could be found 14 days after inoculation; no proteinuria was observed. The second group consisted of the BALB/c (H-2d), BALB.B (H-2b) and DBA/2 (H-2d) strains, which were relatively susceptible to the infection. In these animals proteinuria occurred and a broad polyclonal B-cell stimulation was seen 42 days after inoculation. No correlation was found between the specificity of circulating antibodies and the occurrence of proteinuria or a glomerular fluorescence pattern. These results indicate that in this model non-MHC genes govern the outcome of the infection as well as the development of polyclonal B-cell stimulation and proteinuria.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum laminin P1 fragment concentration in renal diseases

The serum concentration of laminin P1 fragment was determined in various histologically proven renal diseases by a competitive radioimmunoassay directed against the pepsin-resistant fragment P1. The serum laminin P1 fragment level of healthy subjects (n = 71) was 1.35 +/- 0.19 U/ml. Serum levels of laminin P1 fragment in patients with minimal change nephrosis in the remission phase and those with IgA nephropathy showed no significant difference when compared with healthy controls. However, patients with minimal change nephrosis in the nephrotic phase, membranous glomerulonephritis, diabetic nephropathy, lupus nephritis and renal cell carcinoma showed significantly higher levels (P less than 0.01) of serum laminin P1 fragment. No correlation was observed between serum laminin P1 fragment level and creatinine clearance. These results suggest that changes in serum laminin P1 fragment level could be used to indicate alterations in glomerular basement membrane metabolism in renal disease.

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

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

Antigenicity of basement membrane fractions obtained from rat seminiferous tubules

A noncollagenous fraction of basement membrane (D-STBM) obtained from rat testes was submitted to sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE), and eight well-defined bands were detected. A cross-reaction with an antiserum against laminin was revealed by immunoblotting in five bands, with molecular weights ranging from 54 to 64 kDa. No further resolution of these components could be obtained by size exclusion and ionic exchange chromatography. Fifty-two percent of the rats immunized with D-STBM and adjuvants developed a mild multifocal damage of the testis. The lesions were characterized by foci of seminiferous tubules with different degrees of sloughing and/or atrophy of the germinal epithelium. Giant multinucleated cells were frequently seen, and mild interstitial mononuclear cell infiltrates were also detected. By immunofluorescence, deposits of rat IgG with a faint discontinuous linear pattern were observed along the walls of the seminiferous tubules. Circulating antibodies to D-STBM were detected by ELISA in 100% of the rats, whereas in a cross-reaction with laminin antibodies were detected in only 63%. All rats studied revealed a positive delayed type of hypersensitivity (DTH) response to D-STBM. None of the control rats injected with saline and adjuvants presented circulating antibodies to D-STBM or laminin or a positive DTH reaction to D-STBM. Some control group rats (10%) revealed few isolated seminiferous tubules with some degree of sloughing of the germinal epithelium.

Autoantibodies to laminin and other basement membrane proteins in sera from monkeys with histories of reproductive failure identified by cultures of whole rat embryos

Head-fold-stage rat embryos cultured on sera taken from monkeys with histories of reproductive failure had an abnormality frequency of 97% compared with only 7% on sera taken from monkeys with excellent reproductive histories. For a group of these poor reproducers, the toxicity of their sera was associated with the immunoglobulin G (IgG) fraction. These IgG fractions bound to Reichert's membrane and other basement membranes of the embryo. For one monkey, the IgG specifically reacted with a 41 kDa polypeptide of Reichert's membrane, while for two others binding was to laminin, type IV collagen, and several other minor polypeptides of Reichert's membrane. For serum from one monkey, the toxicity to cultured rat embryos was eliminated by absorption with laminin but not type IV collagen.

A murine nephritogenic monoclonal anti-DNA autoantibody binds directly to mouse laminin, the major non-collagenous protein component of the glomerular basement membrane

The interaction of the murine monoclonal anti-DNA antibody H241 with extracellular glomerular antigens was found to be due to the binding of this antibody to laminin, the major non-collagenous protein constituent of the glomerular basement membrane. This interaction is specific, since it is inhibited by laminin, double-stranded DNA and single-stranded DNA in solution. Furthermore, the binding of H241 to mouse laminin is mediated by conformational properties of the antigen because mild denaturation of laminin strongly decreases the binding capacity of H241, while exposure of laminin to sodium dodecyl sulfate, completely abolishes this interaction. H241 is able to bind to both, human and mouse laminin. These findings are in agreement with the ligand binding specificities of the autoantibodies spontaneously produced, that differ from those generated by artificial immunization. We conclude that the polyreactivity of H241 that confers to it the capacity to bind laminin, may account for its ability to form immune deposits by binding directly to non-DNA glomerular antigens.

Testis lesions and cellular and humoral immune responses induced in rats by immunization with laminin

Sixty-six percent of rats immunized with laminin isolated from a mouse Engelbreth-Holm-Swarm (EHS) sarcoma developed moderate lesions in the testis characterized by multiple foci of seminiferous tubules with different degrees of sloughing of the germinal epithelium or atrophy intermingled with normal histological areas. Interstitial mononuclear cell infiltrates were seen in the epididymis. By electron microscopy, pathological changes in the basement membranes of the seminiferous tubules, such as splitting and focal thickenings of knob-like projections toward the epithelium, were observed. Moreover, Sertoli cell cytoplasm showed dilated smooth endoplasmic reticulum and large vacuoles. By electron microscopy with the immunoperoxidase technique, staining for in vivo-bound rat IgG was detected along the walls of the seminiferous tubules as a bright linear immunofluorescence and as a dense reaction product on the basal lamina. High titers of circulating antilaminin antibodies were detected by ELISA in all the rats immunized with laminin. As revealed by the skin test, a delayed type hypersensitivity reaction to laminin was observed in these rats.

Interactions of fibronectin with Treponema pallidum

The adhesive or opsonic glycoprotein, fibronectin, is associated with the surface of Treponema pallidum as shown by immunofluorescence. A quantitative assay using iodine-125 (125I) showed that T pallidum harvested seven days after infection bound more fibronectin than T pallidum harvested 14 days after infection. This increased binding by "younger" organisms was confirmed by radioimmunoassay techniques. Fibronectin appears to have a role in treponemal attachment. Preincubation of T pallidum with goat or rabbit antibody to fibronectin blocked treponemal attachment to cultured cells and to isolated capillaries and inhibited treponemal virulence. Treponemes were incubated in glass wool columns pretreated with fibronectin and were then eluted from the columns. This technique yielded a population of T pallidum that failed to bind to fibronectin. Compared with treponemes eluted from control ovalbumin columns, organisms eluted from fibronectin columns attached to cultured cells in larger numbers but did not survive as long and were not as virulent. Findings are discussed in terms of the relevance of interaction between treponemes and fibronectin in the pathogenesis of T pallidum.