Granulomatous Thyroiditis: A Case Report and Literature Review

BACKGROUND

Granulomatous disease in the thyroid gland has been linked to viral, bacterial and autoimmune etiologies. The most common granulomatous disease of the thyroid is subacute granulomatous thyroiditis, which is presumed to have a viral or post-viral inflammatory cause. Bacterial etiologies include tuberculosis, actinomycosis, and nocardiosis, but are extremely rare. Disseminated actinomycosis and nocardiosis more commonly affect organ-transplant patients with the highest susceptibility within the first year after transplant surgery.

CASE

A 45-year-old African American male, who received his third kidney transplant for renal failure secondary to Alport Syndrome, presented with numerous subcutaneous nodules and diffuse muscle pain in the neck. Further workup revealed bilateral nodularity of the thyroid. Fine needle aspiration of these nodules demonstrated suppurative granulomatous thyroiditis. Subsequent right thyroid lobectomy showed granulomatous thyroiditis with filamentous micro-organisms, morphologically resembling Nocardia or Actinomyces.

CONCLUSION

Disseminated granulomatous disease presenting in the thyroid is very rare, and typically afflicts immune-compromised patients. The overall clinical, cytologic and histologic picture of this patient strongly points to an infectious etiology, likely Nocardia, in the setting of recent organ transplantation within the last year.

Progression of Alport Kidney Disease in Col4a3 Knock Out Mice Is Independent of Sex or Macrophage Depletion by Clodronate Treatment

Alport syndrome is a genetic disease of collagen IV (α3, 4, 5) resulting in renal failure. This study was designed to investigate sex-phenotype correlations and evaluate the contribution of macrophage infiltration to disease progression using Col4a3 knock out (Col4a3KO) mice, an established genetic model of autosomal recessive Alport syndrome. No sex differences in the evolution of body mass loss, renal pathology, biomarkers of tubular damage KIM-1 and NGAL, or deterioration of kidney function were observed during the life span of Col4a3KO mice. These findings confirm that, similar to human autosomal recessive Alport syndrome, female and male Col4a3KO mice develop renal failure at the same age and with similar severity. The specific contribution of macrophage infiltration to Alport disease, one of the prominent features of the disease in human and Col4a3KO mice, remains unknown. This study shows that depletion of kidney macrophages in Col4a3KO male mice by administration of clodronate liposomes, prior to clinical onset of disease and throughout the study period, does not protect the mice from renal failure and interstitial fibrosis, nor delay disease progression. These results suggest that therapy targeting macrophage recruitment to kidney is unlikely to be effective as treatment of Alport syndrome.

Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis

BACKGROUND

In Goodpasture's disease, circulating autoantibodies bind to the noncollagenous-1 (NC1) domain of type IV collagen in the glomerular basement membrane (GBM). The specificity and molecular architecture of epitopes of tissue-bound autoantibodies are unknown. Alport's post-transplantation nephritis, which is mediated by alloantibodies against the GBM, occurs after kidney transplantation in some patients with Alport's syndrome. We compared the conformations of the antibody epitopes in Goodpasture's disease and Alport's post-transplantation nephritis with the intention of finding clues to the pathogenesis of anti-GBM glomerulonephritis.

METHODS

We used an enzyme-linked immunosorbent assay to determine the specificity of circulating autoantibodies and kidney-bound antibodies to NC1 domains. Circulating antibodies were analyzed in 57 patients with Goodpasture's disease, and kidney-bound antibodies were analyzed in 14 patients with Goodpasture's disease and 2 patients with Alport's post-transplantation nephritis. The molecular architecture of key epitope regions was deduced with the use of chimeric molecules and a three-dimensional model of the alpha345NC1 hexamer.

RESULTS

In patients with Goodpasture's disease, both autoantibodies to the alpha3NC1 monomer and antibodies to the alpha5NC1 monomer (and fewer to the alpha4NC1 monomer) were bound in the kidneys and lungs, indicating roles for the alpha3NC1 and alpha5NC1 monomers as autoantigens. High antibody titers at diagnosis of anti-GBM disease were associated with ultimate loss of renal function. The antibodies bound to distinct epitopes encompassing region E(A) in the alpha5NC1 monomer and regions E(A) and E(B) in the alpha3NC1 monomer, but they did not bind to the native cross-linked alpha345NC1 hexamer. In contrast, in patients with Alport's post-transplantation nephritis, alloantibodies bound to the E(A) region of the alpha5NC1 subunit in the intact hexamer, and binding decreased on dissociation.

CONCLUSIONS

The development of Goodpasture's disease may be considered an autoimmune "conformeropathy" that involves perturbation of the quaternary structure of the alpha345NC1 hexamer, inducing a pathogenic conformational change in the alpha3NC1 and alpha5NC1 subunits, which in turn elicits an autoimmune response. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.)

The alloantigenic sites of alpha3alpha4alpha5(IV) collagen: pathogenic X-linked alport alloantibodies target two accessible conformational epitopes in the alpha5NC1 domain

Anti-glomerular basement membrane (GBM) antibody nephritis is caused by an autoimmune or alloimmune reaction to the NC1 domains of alpha3alpha4alpha5(IV) collagen. Some patients with X-linked Alport syndrome (XLAS) develop post-transplant nephritis mediated by pathogenic anti-GBM alloantibodies to collagen IV chains present in the renal allograft but absent from the tissues of the patient. In this work, the epitopes targeted by alloantibodies from these patients were identified and characterized. All XLAS alloantibodies recognized conformational epitopes in the NC1 domain of alpha5(IV) collagen, which were mapped using chimeric alpha1/alpha5 NC1 domains expressed in mammalian cells. Allograft-eluted alloantibodies mainly targeted two conformational alloepitopes mapping to alpha5NC1 residues 1-45 and 114-168. These regions also encompassed the major epitopes of circulating XLAS alloantibodies, which in some patients additionally targeted alpha5NC1 residues 169-229. Both kidney-eluted and circulating alloantibodies to alpha5NC1 distinctively targeted epitopes accessible in the alpha3alpha4alpha5NC1 hexamers of human GBM, unlike anti-GBM autoantibodies, which targeted sequestered alpha3NC1 epitopes. The results identify two immunodominant alpha5NC1 epitopes as major alloantigenic sites of alpha3alpha4alpha5(IV) collagen specifically implicated in the pathogenesis of post-transplant nephritis in XLAS patients. The contrast between the accessibility of these alloepitopes and the crypticity of autoepitopes indicates that distinct molecular forms of antigen may initiate the immunopathogenic processes in the two forms of anti-GBM disease.

Immunohistochemical study for the diagnosis of Alport's syndrome

BACKGROUND

Alport's syndrome (AS) is the most common cause of inherited glomerular disease in Thailand. The majority of cases show X-linked inheritance, which is caused by mutations in the gene coding for the alpha5 chain of type IV collagen in the glomerular basement membrane (GBM) and epidermal basement membrane (EBM). Such mutation usually leads to a reduction in protein amount, thus, immunohistochemical studies have been considered in diagnostic evaluation.

OBJECTIVE

To study the expression of alpha[IV] collagen chains in the skin as an alternative approach to diagnose AS.

MATERIAL AND METHOD

Eleven unrelated probands with proven AS, 7 relatives with abnormal urinalysis, 4 suspected individuals, and 8 normal controls were enrolled. A punch skin biopsy and immunofluorescence staining of the tissue specimens for alpha1, alpha3 and alpha5[IV] collagen chains was performed.

RESULTS

The alpha5[IV] chain was absent in the EBM in all male AS patients while a discontinuing pattern was observed in all females except one. The findings are specific for AS with a sensitivity of 91%. Studies in relatives and suspected individuals also confirmed the advantage of this approach as demonstrated by the absence and discontinuation of alpha5[IV] staining in all males and females, respectively. We also analyzed their expressions in the kidney tissue and demonstrated abnormal alpha3 and alpha5[IV] staining in five of six samples.

CONCLUSION

Immunohistochemical study of the skin should be used as a screening method in patients suspected of AS, as it is much less invasive. Moreover, it is a useful adjunct to conventional examination of biopsied renal tissue.

Gene expression analysis in a canine model of X-linked Alport syndrome

Chronic kidney disease (CKD) often culminates in renal failure as a consequence of progressive interstitial fibrosis and is an important cause of illness and death in dogs. Identification of disease biomarkers and gene expression changes will yield valuable information regarding the specific biological pathways involved in disease progression. Toward these goals, gene expression changes in the renal cortex of dogs with X-linked Alport syndrome (XLAS) were examined using microarray technology. Extensive changes in inflammatory, metabolic, immune, and extracellular matrix biology were revealed in affected dogs. Statistical analysis showed 133 genes that were robustly induced or repressed in affected animals relative to age-matched littermates. Altered expression of numerous major histocompatibility complex (MHC) molecules suggests that the immune system plays a significant role in XLAS. Increased expression of COL4A1 and TIMP-1 at the end stage of disease supports the suggestion that expression increases in association with progression of fibrosis and confirms an observation of increased COL4A1 protein expression. Clusterin may function as one of the primary defenses of the renal cortex against progressive injury in dogs with XLAS, as demonstrated here by increased CLU gene expression. Cellular mechanisms that function during excess oxidative stress might also act to deter renal damage, as evidenced by alterations in gene expression of SOD1, ACO1, FDXR, and GPX1. This investigation provides a better understanding of interstitial fibrosis pathogenesis, and potential biomarkers for early detection, factors that are essential to discovering more effective treatments thereby reducing clinical illness and death due to CKD.

Renal transplantation in patients with Alport syndrome

For pediatric kidney transplant physicians, two aspects of Alport syndrome set the disease apart from other causes of terminal renal failure. First, an understanding of the genetics of Alport syndrome is needed to make appropriate decisions regarding potential related kidney donors to Alport patients requiring renal transplantation. Second, renal transplantation for Alport syndrome may be complicated by post-transplant anti-GBM nephritis, a problem that is nearly unique to this disease. This review discusses these aspects of Alport syndrome and attempts to provide rational recommendations for clinicians.

Hereditary nephritis mimicking immune complex-mediated glomerulonephritis

The defining ultrastructural features of hereditary nephritis are "basket weave" lamellation or thinning of glomerular basement membranes. Electron-dense deposits are not seen and immunofluorescence (IF) is generally negative. In this study, we report 5 cases of hereditary nephritis in which substantial amounts of glomerular electron-dense deposits were identified on electron microscopy, with corresponding positive IF staining in 4 cases, suggesting immune complex-mediated glomerulonephritis. However, no case had histological evidence of glomerular endocapillary or extracapillary proliferation or leukocyte infiltration typical of active glomerulonephritis. Four cases were diagnosed at outside institutions simply as forms of glomerulonephritis without considering the possibility of hereditary nephritis and were sent for consultation in contemplation of possible immunosuppressive therapy. All patients had negative serologies and no known underlying infectious or autoimmune disease; 4 patients had family history of hematuria or renal disease. The glomerular electron-dense deposits were predominantly mesangial (4 cases) and intramembranous (4 cases), as well as subepithelial (2 cases) or subendothelial (1 case). Corresponding IF positivity for immune reactants was identified in 4 cases, and IgG was the predominant immunoglobulin deposited. A characteristic feature was the tendency for deposits to form between the complex layers of glomerular basement membrane material, favoring a process of nonspecific entrapment of immune reactants within the thickened, lamellated basement membrane. In all cases, a diagnosis of hereditary nephritis was confirmed by demonstration of the characteristic loss of immunoreactivity for the alpha5 subunit of collagen IV (4 cases) or Goodpasture's antigen (1 case) in renal or epidermal basement membranes. These cases expand the spectrum of unusual pathological findings in hereditary nephritis and emphasize the potential for hereditary nephritis to mimic immune complex glomerulonephritis.

Nephroprotection by antifibrotic and anti-inflammatory effects of the vasopeptidase inhibitor AVE7688

BACKGROUND

Chronic renal disease substantially increases the risk of cardiovascular events and death. Vasopeptidase inhibitors are known to show a strong antihypertensive effect. In the present study, we investigated the nephroprotective potential of the vasopeptidase inhibitor AVE7688 beyond its antihypertensive effects in a mouse model of progressive renal fibrosis.

METHODS

COL4A3 -/- mice received 25 mg AVE7688 per kg body weight. Treatment was initiated in week 4 (early) and week 7 (late). Eight mice per group were sacrificed after 7.5 or 9.5 weeks, and serum levels of urea, systemic blood pressure, and proteinuria were measured. Renal tissue was investigated by routine histology, electron microscopy, immunohistochemistry, and Western blotting. Lifespan until death from renal fibrosis was monitored.

RESULTS

Lifespan of treated mice increased by 143% (early therapy) and by 53% (late therapy) compared to untreated animals (172 +/- 19 vs. 109 +/- 15 vs. 71 +/- 6 days, P < 0.01). Untreated COL4A3 -/- mice did not develop severe hypertension (mean systolic blood pressure 116 +/- 14 vs. 111 +/- 9 mm Hg in wild-type mice), and both therapies mildly reduced systemic blood pressure (107 +/- 13 and 105 +/- 14 mm Hg, data not significant). AVE7688 decreased proteinuria from 12 +/- 3 g/L in untreated mice to 2 +/- 1 g/L (early) and to 4 +/- 1 g/L (late therapy, P < 0.05), as well as serum-urea from 247 +/- 27 to 57 +/- 10 and to 105 +/- 20 mmol/L (P < 0.05). Extent of fibrosis, inflammation, and profibrotic cytokines was reduced by AVE7688 therapy.

CONCLUSION

The results indicate a strong nephroprotective effect of the vasopeptidase inhibitor in this animal model of progressive renal fibrosis. Besides the antihypertensive action of AVE7688, its antifibrotic, anti-inflammatory, and antiproteinuric effects demonstrated in the present study may serve as an important therapeutic option for chronic inflammatory and fibrotic diseases in man.

An unusual case of pulmonary-renal syndrome associated with defects in type IV collagen composition and anti-glomerular basement membrane autoantibodies

Commercial serological assays for the presence of anti-glomerular basement membrane (GBM) antibodies are thought to be indicative of Goodpasture's syndrome. We report a case in which commercial tests inaccurately suggested that a patient with a pulmonary-renal syndrome had Goodpasture's disease. Additional laboratory testing using recombinant type IV collagen NC1 domain proteins showed that the autoantibodies in question were not directed against the Goodpasture antigen (the alpha3NC1 domain), but against the alpha2NC1 domain of type IV collagen. Our findings represent the first known case of human autoantibodies to the alpha2NC1 domain. Further investigation showed that this patient has decreased alpha3 and alpha5 chain expression in the GBM and defects in type IV collagen, resembling abnormalities in patients with Alport's syndrome.

Retransplantation in Alport post-transplant anti-GBM disease

BACKGROUND

Post transplant anti-glomerular basement membrane (GBM) disease affects up to 5% of patients with Alport's syndrome. Defects in the COL4A5 gene are responsible for most cases, and alpha 5(IV)NC1 is the usual target for alloantibodies. Gene deletions are more commonly associated with this complication than are point mutations. The disease is severe in renal allografts and nearly always results in graft loss.

METHODS

Three cases of retransplantation in Alport's syndrome are described here in detail. All cases were started on immunosuppressive therapy early in the course of their disease and one patient (case 2) received pre-emptive anti-T-cell therapy (Campath IH). Anti-GBM antibodies in these cases were investigated by standard anti-GBM enzyme-linked immunosorbent assay (ELISA), by indirect immunofluorescence, and by Western blotting using collagenase-digested human GBM and recombinant type IV collagen NC1 domains made in insect cells.

RESULTS

All cases showed early antibody and complement fixation to human GBM. Target alloantibodies were to alpha 5(IV)NC1 domain predominantly. Cases two and three gave negative results on standard ELISA for anti-GBM antibodies. Pathologic examination revealed crescentic glomerulonephritis, which was rapid in onset in case 1, blunted and less aggressive in case 3, and case 2 developed segmental necrosis without crescent formation. Neutrophilic infiltrates were an early feature in all 3 cases. All cases are compared with a review of all retransplanted cases in the literature.

CONCLUSION

Alport anti-GBM disease is a severe disease in retransplanted patients. Anti-T-cell therapy seemed to modify the pathologic findings but did not prevent graft loss. Longer term plasma exchange and mycophenolate mofetil may attenuate the illness, but in these cases did not prevent graft loss. Western blotting detected alloantibodies to alpha 5(IV) NC1 domain and is more sensitive and specific for this disease than standard ELISAs.

CD151, the first member of the tetraspanin (TM4) superfamily detected on erythrocytes, is essential for the correct assembly of human basement membranes in kidney and skin

Tetraspanins are thought to facilitate the formation of multiprotein complexes at cell surfaces, but evidence illuminating the biologic importance of this role is sparse. Tetraspanin CD151 forms very stable laminin-binding complexes with integrins alpha3beta1 and alpha6beta1 in kidney and alpha3beta1 and alpha6beta4 in skin. It is encoded by a gene at the same position on chromosome 11p15.5 as the MER2 blood group gene. We show that CD151 expresses the MER2 blood group antigen and is located on erythrocytes. We examined CD151 in 3 MER2-negative patients (2 are sibs) of Indian Jewish origin with end-stage kidney disease. In addition to hereditary nephritis the sibs have sensorineural deafness, pretibial epidermolysis bullosa, and beta-thalassemia minor. The 3 patients are homozygous for a single nucleotide insertion (G383) in exon 5 of CD151, causing a frameshift and premature stop signal at codon 140. The resultant truncated protein would lack its integrin-binding domain. We conclude that CD151 is essential for the proper assembly of the glomerular and tubular basement membrane in kidney, has functional significance in the skin, is probably a component of the inner ear, and could play a role in erythropoiesis.

Alport syndrome: HLA association and kidney graft outcome

Alport syndrome (AS) is a genetic disease of type IV collagen involving non-homogeneous patterns of inheritance characterized clinically by the presence of progressive haematuric nephritis leading to end-stage renal disease (ESRD), hearing loss and/or ophthalmologic abnormalities. The aim of this study was to investigate, in a cohort of AS patients who had undergone a kidney graft (KG) or who were still on a waiting list for a KG, (a) whether there is a correlation between AS and HLA antigen expression, and (b) long-term graft outcome in transplant patients. The AS cohort was represented by 34 ESRD patients, of whom 25 received a KG and the remaining nine were still on a waiting list. AS transplant patients represented 2.78% of 899 first KGs performed at our centre (Transplantation Department at S. Martino Hospital, Genoa) between 1983 and 2002. Grafts were procured from cadaveric donors in 18 cases and from living, related donors in seven cases. All AS transplant patients had a post-transplant follow-up period of at least 12 months. Results showed that: (i) the frequency of the HLA-DRB1*16 antigen was significantly increased in the whole AS cohort as compared to 128 healthy subjects (HS) (corrected P-value 0.0026; relative risk 7.20) as well as to 232 non-AS ESRD patients on a waiting list for KG (corrected P-values 0.0156; relative risk 4.67); (ii) 5- and 10-year graft survivals in the AS transplant patients were 80 and 73%, respectively, and did not differ from those of a control group represented by 25 non-AS KG recipients matched for sex, age, number of HLA mismatches and immunosuppressive treatment. Increased frequency of HLA-DRB1*16 in AS patients may reflect a linkage disequilibrium with genes coding for collagen synthesis.

Allograft rejection and glomerular basement membrane antibodies in Alport's syndrome

BACKGROUND

Anti-glomerular basement membrane (GBM) antibodies occasionally occur in Alport patients after renal allograft transplantation.

METHODS

We report a patient with Alport's syndrome who lost four transplants each within the first year post transplantation. We searched for the presence of anti-GBM antibodies using recombinant NC1 domains of type IV collagen. Immunoblotting, enzyme linked immunosorbent assay (ELISA), and immunofluorescence were used to detect the presence of antibodies against the glomerular basement membrane.

RESULTS

High antibody titers to the alpha3 chain (the Goodpasture antigen) and alpha5 chain of type IV collagen were detected. Review of pathologic specimens showed features of vascular rejection in all specimens.

CONCLUSION

The association of high titer anti-GBM antibodies and vascular rejection may be important. When vascular rejection occurs in Alport patients, the presence of anti-GBM antibodies should be sought. Recombinant anti-GBM assays should be used if standard anti-GBM testing is equivocal.

High affinity of anti-GBM antibodies from Goodpasture and transplanted Alport patients to alpha3(IV)NC1 collagen

BACKGROUND

Anti-glomerular basement membrane (anti-GBM) antibody-mediated diseases are characterized by rapidly progressive glomerulonephritis (RPGN) that often results in irreversible loss of renal function and renal failure. Although many factors contribute to the fulminant nature and treatment resistance of this disease, we questioned whether high affinity autoantibody-alpha3(IV) collagen interactions lead to persistent antibody deposition, thereby perpetuating inflammation. To address this hypothesis, the binding kinetics of human anti-GBM antibodies (Ab) to alpha3(IV)NC1 were evaluated using an optical biosensor interaction analysis.

METHODS

Polyclonal anti-GBM Abs were purified by alpha3(IV)NC1 affinity chromatography from the sera of patients with anti-GBM AB-mediated diseases, including individuals with Goodpasture syndrome (GS), idiopathic RPGN (N = 7), and Alport syndrome (AL) following kidney transplantation (N = 4). The affinity-binding characteristics of the autoantibodies were determined using a biosensor analysis system, with immobilized bovine alpha3(IV)NC1 dimers.

RESULTS

All of the autoantibody preparations bound to alpha3(IV)NC1, whereas none bound to alpha1(IV)NC1 (control). Purified, normal serum IgG did not bind to either antigen. Estimated dissociation constants (Kd) for the purified autoantibodies were 1.39E-04 +/- 7.30E-05 s-l (GS) and 8. 90E-05 +/- 2.80E-05 s-l (AL). Their estimated association constants (Ka) were 2.67E+04 +/- 1.8E+04 (M-ls-l) and 2.76E+04 +/- 1. 70E+04(M-ls-l) for GS and AL patients, respectively. By comparison with other Ab interactions, these Abs demonstrated high affinity, with relatively high on (binding) rates and slow off (dissociation) rates.

CONCLUSIONS

The results suggest that anti-GBM Abs bind rapidly and remain tightly bound to the GBM in vivo. This property likely contributes to both the fulminant nature of this disease and its resistance to therapy, because persistent glomerular Ab deposition has the potential to produce continuous inflammation, despite removal of circulating Abs and adequate immunosuppression.

Identification of alpha3, alpha4, and alpha5 chains of type IV collagen as alloantigens for Alport posttransplant anti-glomerular basement membrane antibodies

BACKGROUND

Alport syndrome is a hereditary disorder of basement membranes especially affecting the kidneys, ears, and eyes. Some patients who undergo renal transplantation lose their kidneys as a result of posttransplant anti-glomerular basement membrane (anti-GBM) disease.

METHODS

In the present study, we analyzed serum from 21 unselected Alport patients who underwent renal transplantation. Eleven samples were from patients without posttransplant anti-GBM nephritis, and 10 were from patients with this disease.

RESULTS

Thirteen serum samples [10 alport posttransplant nephritis serum (APTN) and three Alport posttransplant serum (APT)] revealed linear binding to the GBM by indirect immunofluorescence. By using direct ELISA and immunoblotting with GBM constituents and type IV collagen NC1 domains from bovine, human, and recombinant sources, we detected anti-GBM antibodies in all Alport patients in varying titers. Five samples showed specific reactivity to the alpha3 chain, four to the alpha5 chain, six to both alpha3 and alpha5 chains, one to the alpha3 and alpha4 chains, and two to the alpha3, alpha4, and alpha5 chains of type IV collagen. The varied spectrum of reactivities was present equally in nephritic and non-nephritic sera. Ten control samples from non-Alport transplant patients did not exhibit specific binding to the GBM.

CONCLUSIONS

These results suggest that the absence of alpha3, alpha4, and alpha5 chains of type IV collagen in the Alport kidney leads to alloantibodies in all Alport patients who receive transplants, irrespective of whether they develop nephritis or not. Although all Alport transplant patients develop this humoral response, only a select few develop anti-GBM disease. We suggest that this difference could be attributable to a genotypic effect on the ability of some individuals to launch a cell-mediated immune response.

Rapidly progressive glomerulonephritis

The management of rapidly progressive glomerulonephritis has been transformed over the past thirty years. It has become one of the few forms of glomerulonephritis that can be effectively treated, and today overall renal survival is as high as 70%. Effective management of patients with RPGN requires prompt and accurate diagnosis so that patients are appropriately treated, and long term follow up to minimise the risk of relapse in patients with some types of those disease.

LINE-1 elements at the sites of molecular rearrangements in Alport syndrome-diffuse leiomyomatosis

Deletions encompassing the 5' termini of the paired type IV collagen genes COL4A5 and COL4A6 on chromosome Xq22 give rise to Alport syndrome (AS) and associated diffuse leiomyomatosis (DL), a syndrome of disseminated smooth-muscle tumors involving the esophagus, large airways, and female reproductive tract. In this study, we report isolation and characterization of two deletion junctions. The first, in a patient described elsewhere, arose by a nonhomologous recombination event fusing a LINE-1 (L1) repetitive element in intron 1 of COL4A5 to intron 2 of COL4A6, resulting in a 13.4-kb deletion. The second, in a previously undescribed family, arose by unequal homologous recombination between the same L1 and a colinear L1 element in intron 2 of COL4A6, resulting in a>40-kb deletion. L1 elements have contributed to the emergence of this locus as a site of frequent recombinations by diverse mechanisms. These give rise to AS-DL by disruption of type IV collagen and perhaps other as yet unidentified genes, evidenced by deletions as small as 13.4 kb.

Association of Alport's syndrome with HLA-DR2 antigen in a group of unrelated patients

A few family studies have evaluated HLA antigens in Alport's syndrome; however, there are no large population studies. In the present report, we studied 40 unrelated white patients with Alport's syndrome seen at the Unit of Renal Transplantation, Faculty of Medicine of Ribeirão Preto, São Paulo, Brazil. HLA-A, -B, -DR and -DQ antigens were typed using a complement-dependent microlymphocytotoxicity assay. A control white population (N = 403) from the same geographical area was also typed for HLA antigens. Although the frequencies of HLA-A and -B antigens of patients were not statistically different from controls, the frequency of HLA-DR2 antigen observed in patients (65%) was significantly increased in relation to controls (26%; P < 0.001). The relative risk and etiologic fraction for HLA-DR2 antigen were 5.2 and 0.525, respectively. Although few immunological abnormalities have been shown in Alport's syndrome, in this report we emphasize the association of HLA molecules and Alport's syndrome. Besides the well-known inherited molecular defects encoded by type IV collagen genes in Alport's syndrome, the major histocompatibility alleles may be in linkage disequilibrium with these defective collagen genes.

Targets of alloantibodies in Alport anti-glomerular basement membrane disease after renal transplantation

A minority of patients with Alport syndrome develop anti-GBM disease in their allografts after renal transplantation. Clinically, the renal disease appears indistinguishable from Goodpasture's disease of native kidneys, in which the target of autoantibodies had been identified as the NC1 domain of the alpha 3 chain of type IV collagen, alpha 3(IV)NC1. However, in the majority of cases, Alport syndrome is due to mutations in the gene encoding the alpha 5 chain of type IV collagen, located on the X chromosome. Neither chain is detectable in the glomerular basement membrane (GBM) of most patients with Alport syndrome. We investigated the targets of the alloantibodies of 12 Alport patients who developed post-transplant anti-GBM disease by Western blotting onto recombinant NC1 domains made in insect cells. Binding to these antigens, for both typical Goodpasture and Alport anti-GBM antibodies, was strong and conformation-sensitive. Nine antibodies showed selective binding to alpha 5(IV)NC1. This specificity was confirmed by the demonstration of binding to a 26 kDa band of collagenase-solubilized human GBM, and/or binding to normal epidermal as well as renal basement membranes by indirect immunofluorescence. One antibody showed binding to alpha 5 and alpha 3(IV)NC1, while two showed predominant binding to alpha 3(IV)NC1. All seven patients whose pedigree or mutation analysis showed X-linked inheritance had predominant anti-alpha 5 reactivity. One with predominant anti-alpha 3 reactivity had a COL4A3 mutation. These findings show that human anti-GBM disease can be associated with antibodies directed towards different molecular targets. Alpha 5(IV)NC1 is the primary target in most patients with X-linked Alport syndrome who develop post-transplant anti-GBM disease.

Antithyroid and antiadrenal autoantibodies in antiglomerular basement membrane disease, thin basement membrane disease and Alport syndrome

The basement membranes of the glomerulus, thyroid and adrenal all contain the Goodpasture antigen, the target of autoantibodies in antiglomerular basement membrane (GBM) disease. Antithyroid antibodies can be associated with antiGBM disease, and there have been occasional reports of antithyroid antibodies in Alport syndrome, an inherited kidney disease where the GBM lacks the Goodpasture antigen. The aim of this study was to determine how often antithyroid and antiadrenal autoantibodies occurred in antiGBM disease, Alport syndrome and a related condition, thin basement membrane disease (TBMD). Sera from patients with antiGBM disease (n = 19), Alport syndrome (n = 5) or TBMD (n = 13) were tested for antithyroglobulin, antithyroid microsomal and antiadrenal antibodies. Five of the patients with antiGBM disease (5/19, 26%, P NS) had antimicrosomal, and one had antithyroglobulin, antibodies (1/19, 5%, P NS). No patient with Alport syndrome had antithyroid antibodies. One with TBMD (1/13, 8%, P NS) had antithyroglobulin and antimicrosomal antibodies at titres of 1/400 and 1/25,600, respectively. Both patients with antithyroglobulin antibodies had previously been diagnosed with hypothyroidism. No one with antiGBM disease, Alport syndrome or TBMD had antiadrenal antibodies. Antithyroid microsomal antibodies do not occur significantly more often in patients with antiGBM disease than in normals, and antithyroid and antiadrenal antibodies are not associated with Alport syndrome or TBMD.

Identification of post-transplant anti-alpha 5 (IV) collagen alloantibodies in X-linked Alport syndrome

X-linked Alport syndrome (AS) is a heritable disorder which is associated with mutations in the type IV collagen alpha 5 (IV) chain gene (COL4A5) located on chromosome X. Following renal transplantation, an average of 6% of male AS patients develop anti-GBM nephritis. We studied the specificity of the antibodies against type IV collagen in the serum of a patient with COL4A5 partial deletion. The specificity of these alloantibodies was determined against collagenase-digested GBM, as well as against recombinant non-collagenous (NC1) domains of the type IV collagen alpha 1(IV)-alpha 6(IV) chains expressed in escherichia coli. Immunoblotting and ELISA demonstrated that these antibodies bound specifically to the NC1 domain of alpha 5(IV) collagen. There was no binding to the NC1 domain of the other chains, including the Goodpasture antigen. Competitive ELISA confirmed the results obtained by ELISA and immunoblotting. This patient developed alloantibodies directed against antigens present in the grafted kidney, but absent from his Alport kidney. The pathogenesis of post-transplantation glomerulonephritis in the Alport patient studied is thus similar to that of Goodpasture syndrome, with the exception that the pathogenic antibodies are targeted to another alpha chain of type IV collagen.

[New molecular and clinical information about collagens]

Collagen is one of the most abundant proteins in human tissues. Together with other connective tissue components (non-collagenous glycoproteins, proteoglycans, laminins, thrombospondins, entactin and tenascin), collagen promotes cellular adhesion, activates intracellular signals, and regulates the biological activities of growth factors and other proteins. During the past 20 years at least 19 genetically different collagenous proteins coded by 30 distinct genes have been identified. Here, we review some new aspects of the collagens that form fibrils, sheets, or beaded filaments, and of the so-called multiplexin collagens. Whenever possible, we give insights regarding the association of the structural abnormalities of these proteins as they relate with human disease(s).

A COL4A3 gene mutation and post-transplant anti-alpha 3(IV) collagen alloantibodies in Alport syndrome

The X-linked Alport syndrome is associated with mutations and deletions in COL4A5 gene, one of six genes which constitute the alpha-chains of type IV collagen in basement membranes. The autosomal recessive form of Alport syndrome is characterized by mutations and deletions in the COL4A3 and COL4A4 genes. A fraction of Alport patients who undergo renal transplantation develop anti-glomerular basement membrane (GBM) nephritis, which results in loss of the renal allograft function. Recently, the target for alloantibodies from an X-linked Alport patient with complete COL4A5 gene deletion was determined to be the alpha 3 chain of type IV collagen. The present study characterized the post-transplant alloantibodies from an autosomal recessive Alport patient with anti-GBM glomerulonephritis and a COL4A3 gene mutation which predicted a loss of 85% of the alpha 3(IV) NC1 domain. The specificity of these new antibodies were studied using glomerular basement membrane constituents and recombinant type IV collagen domains. The results establish the target for the alloantibodies from an autosomal recessive Alport patient with COL4A3 deletion as principally the alpha 3(IV) collagen chain, similar to the post-transplant alloantibodies from X-linked Alport patients with COL4A5 gene deletions. The absence of alpha 3(IV) chain in the GBM of patients with both these forms of Alport syndrome, due either to a failure of synthesis or a failure of assembly, presumably leads to a loss of immunologic tolerance for the alpha 3(IV) NC1 domain in transplanted allografts.

Bull terrier hereditary nephritis: a model for autosomal dominant Alport syndrome

Bull terrier hereditary nephritis is inherited as an autosomal dominant disease and causes renal failure at variable ages in affected dogs. The aims of this study were to compare the clinical, ultrastructural and immunohistochemical features of bull terrier hereditary nephritis with the characteristics of the human forms of Alport syndrome. Many animals with bull terrier hereditary nephritis have hematuria, and some have anterior lenticonus. However, deafness is not associated with the renal disease, and affected dogs do not have the large platelets that are occasionally seen in patients with autosomal Alport syndrome. The glomerular capillary basement membrane (GCBM) in affected bull terriers has an identical ultrastructural appearance to that seen in X-linked Alport syndrome, with lamellations and intramembranous electron-dense deposits. However, both the Goodpasture and the Alport antigens, which represent parts of the alpha 3(IV) and alpha 5(IV) collagen chains, respectively, are present in the GCBM of affected dogs. Bull terrier hereditary nephritis represents an animal model for autosomal dominant Alport syndrome, and can be used to further examine how genetic mutations affect a basement membrane protein and the corresponding membrane structure.

Anti-glomerular and anti-tubular basement membrane nephritis in a renal allograft recipient with Alport's syndrome

A 28-year-old deaf, white man with a clinical diagnosis of Alport's syndrome since 4 years of age experienced renal failure, fever, and mental status changes suggestive of vasculitis following his first cadaveric renal transplant; these symptoms and changes resolved after removal of the allograft. Immunohistological stains demonstrated intense linear deposition of IgG and C3 in glomerular and tubular basement membranes in the absence of glomerular crescents. One year later, a second renal transplant led to similar symptoms. A biopsy was performed 14 days after engraftment, which demonstrated intense linear deposition of IgG in glomerular and tubular basement membranes, but cellular crescents were not present. A serologic profile was ordered to evaluate the patient further for vasculitis, and during the evaluation, circulating anti-glomerular basement membrane and anti-tubular basement membrane antibodies were identified by indirect immunofluorescence microscopy (titer, > 1:320). An open biopsy specimen obtained during repair of a renal laceration demonstrated a crescentic glomerulonephritis with immunohistologic findings identical to those of previous biopsies. Anti-glomerular basement membrane nephritis should be suspected in any patient with Alport's syndrome in whom progressive renal failure develops following renal transplantation. Detection of anti-glomerular basement membrane/anti-tubular basement membrane antibodies will assure the diagnosis, and early initiation of plasmapheresis may be helpful to prevent further renal damage.

A monoclonal antibody marker for Alport syndrome identifies the Alport antigen as the alpha 5 chain of type IV collagen

The nephropathy of Alport syndrome is associated with unique abnormalities of glomerular basement membranes and is caused in many families by mutations in the X-chromosomal gene COL4A5, which encodes the alpha 5 chain of type IV collagen. We have previously reported that Alport epidermal and glomerular basement membranes fail to bind a monoclonal antibody, Mab A7, that reacts with normal epidermal and glomerular basement membranes, and that this abnormality is unique to Alport syndrome. The molecule in normal tissues that reacts with Mab A7 was termed the "Alport antigen". In the present study we used recombinant carboxyterminal noncollagenous (NC1) domains of the alpha 1, alpha 2, alpha 3, alpha 4 and alpha 5 chains of type IV collagen to determine the molecular identity of the Alport antigen. Mab A7 was found to bind specifically to the NC1 domain of the alpha 5 chain of type IV collagen, by ELISA and immunoblotting studies. This finding provides a molecular explanation for the utility of Mab A7 as a marker for the Alport basement membrane defect. Mab A7 can identify the Alport basement membrane defect in those patients in whom COL4A5 mutations prevent incorporation of alpha 5(IV) into basement membranes.

Immunohistologic studies of type IV collagen in anterior lens capsules of patients with Alport syndrome

BACKGROUND

Alport syndrome is an inherited disorder affecting the kidney, eye and ear arising from mutations in the gene COL4A5, which encodes the alpha 5 chain of type IV collagen. Structural defects of glomerular basement membranes in Alport syndrome are associated in most instances with failure to detect the alpha 3, alpha 4, and alpha 5 chains of type IV collagen as well as the Alport antigen that is identified in normal tissues by a genetically discriminating alloantibody and monoclonal antibody. Anterior lenticonus is an ocular abnormality pathognomic of Alport syndrome that is associated with marked thinning of the anterior lens capsule (ALC). The reactivity of Alport ALC with type IV collagen antibodies has not previously been reported.

EXPERIMENTAL DESIGN

ALCs were obtained at the time of cataract extraction from two unrelated males with Alport syndrome and anterior lenticonus, and stained with antibodies against the alpha 1, alpha 2, alpha 3 and alpha 4 chains of type IV collagen, as well as an antibody against the alpha 5 (IV) chain. Controls consisted of ALCs from a normal individual and from a patient with diabetes mellitus.

RESULTS

Normal and diabetic ALCs reacted with antibodies against the alpha 1, alpha 2, alpha 3, and alpha 4 chains of type IV collagen and the alpha 5 (IV) chain. In one of the Alport patients, ALC showed no reactivity with antibodies against the alpha 5 (IV) chain and the alpha 3 and alpha 4 chains of type IV collagen. In the second patient, ALC reactivity with these antibodies was preserved. Epidermal basement membranes from this second patient also showed reactivity with antibody against the alpha 5 (IV) chain, unlike most males with Alport syndrome. In both Alport patients, ALCs reacted with antibodies against the alpha 1 (IV) and alpha 2 (IV) chains.

CONCLUSIONS

These findings suggest that anterior lenticonus in patients with Alport syndrome may be associated with absence of the alpha 3 and alpha 4 chains of type IV collagen, as well as the alpha 5 (IV) chain, from anterior lens capsule. On the other hand, these chains may be present in Alport patients with anterior lenticonus. The precise structural basis for mechanical weakness of the anterior lens capsule in patients with Alport syndrome remains to be determined.

Inherited diseases of the glomerular basement membrane

The inherited diseases of the glomerular basement membrane include Alport's syndrome (AS), nail-patella syndrome, and thin basement membrane nephropathy. Classical AS is inherited in an X-linked manner and accounts for approximately 85% of the cases. Its manifestations include hematuria, sensorineural hearing loss, ocular defects, and a progression to renal failure. A defect(s) in the alpha 5 (IV) chain of type IV collagen is believed to be the etiology of classic AS, and alterations in its encoding gene localized to the X-chromosome have been elucidated. Although isolated cases of anti-glomerular basement membrane glomerulonephritis have been reported following renal transplantation in patients with AS, it is considered an effective form of renal replacement therapy. Less is known regarding the genetic basis of the autosomal-dominant form of AS, which apparently accounts for the remaining 15% of the cases. Nail-patella syndrome is characterized by nail dysplasia, patellar hypoplasia or aplasia, and nephropathy. It is inherited in an autosomal-dominant fashion with the gene locus assigned to the long arm of chromosome 9. Possible linkage between the COL5A1 gene and the gene for nail-patella syndrome has been suggested. Approximately 30% of the patients progress to end-stage renal failure. Renal transplantation has been successful in treating patients who progress to end-stage renal failure. Thin basement membrane nephropathy is an autosomal dominant trait that accounts for approximately 30% of the cases presenting as persistent, asymptomatic hematuria. The cause of thin basement membrane nephropathy is unknown at present. No decline in renal function is associated with thin basement membrane nephropathy.

COL4A5 gene deletion and production of post-transplant anti-alpha 3(IV) collagen alloantibodies in Alport syndrome

Mutations in the COL4A5 gene encoding the alpha 5(IV) chain of type IV collagen have been implicated as the primary defect in X-linked Alport syndrome. Several kinds of mutations have been reported so far, spanning point mutations to complete gene deletions. About 5% of Alport patients, who undergo renal transplantation, develop anti-glomerular basement membrane (GBM) nephritis, causing loss of allograft function. In one such patient, COL4A5 gene deletion was recently identified. In the present study, the GBM constituent, targeted by the anti-GBM alloantibodies from the patient who had complete COL4A5 gene deletion was identified. Its identity was determined on the basis of circulating antibody binding to various GBM constituents, domains of bovine type IV collagen and recombinant NC1 domain of human type IV collagen. These results establish, for the first time, the absence of the alpha 5(IV) chain in Alport GBM and, in the same patient, the production of an alloantibody that is targeted to a different chain of type IV collagen, the alpha 3(IV) chain. These findings provide further support for the hypothesis that: (1) anti-alpha 3(IV) collagen alloantibodies mediate the allograft glomerulonephritis; and (2) COL4A5 gene mutations cause defective assembly of the alpha 3(IV) collagen alloantibodies mediate the allograft glomerulonephritis; and (2) COL4A5 gene mutations cause defective assembly of the alpha 3(IV) chain in Alport GBM, as reflected by the production of anti-alpha 3(IV) alloantibodies.

[Alport's syndrome: new findings]

The Alport's syndrome is a disease characterized by a symptomatic triad: nephropathy, hypoacusia and ocular alterations. This syndrome is genetically heterogeneous and results from numerous mutations in COL4A5 gene, whose locus resides on the long arm of the X chromosome (Xq22). This gene codifies for IV collagen alpha 5 chain, which is a fundamental constituent of the glomerular, lens and Corti's organ basal membranes. Present knowledge on molecular genetics and the characterization of the different mutations that affect the Alport's gene will lead to classification of this syndrome in subtypes, according to those mutations, and to its phenotypic expressions; in addition, some syndromes, phenotypically similar, will probably have to be distinguished from Alport's disease, in a future, if a genetic alteration is found in genes other than COL4A5.

Immunogenetic findings in glomerulonephritis

In the 19th century, several authors recognized that some renal diseases tend to run in families. Alport pointed to the constellation of nephritic urinary sediment, hearing loss and progression into renal failure. Today this is recognized to result from abnormal basement membrane (BM) collagen synthesis. Recently it has been recognized, however, that other forms of glomerulonephritis may also run in families. In about 10% of patients with glomerulonephritis one or more sibling also suffers from glomerulonephritis. Genetically determined derangements of immune regulation may play a role in the genesis of primary chronic glomerulonephritis. Potentially associated immunogenetic abnormalities include inherited defects of the complement system, increased prevalence of certain HLA-types, altered frequencies of polymorphisms in immunoglobulins and TCR genes and others. This overview summarizes immunogenetic studies performed in patients with glomerulonephritis with special emphasis on patients with mesangial IgA GN.

Alport syndrome diagnosed by immunofluorescence using a new monoclonal antibody

A 14-year-old female with microscopic hematuria was admitted for a renal biopsy. She had a family history of renal disease without deafness. The findings of light microscopy and conventional immunofluorescence were normal. Electron microscopy showed a diffuse thinning of the glomerular basement membrane (GBM) with its mild splitting. Irregular thickening of GBM and glomerular small dense particles was not observed. Thin basement membrane syndrome was suspected from these findings. However, it was difficult to differentiate from Alport syndrome. Immunofluorescence analysis using the monoclonal antibody to the 28-kilodalton monomers of the noncollagenous domain of type IV collagen verified the diagnosis of heterozygous Alport syndrome.

Laminin, fibronectin, and Goodpasture antigen detection in patients with Alport's syndrome

Indirect immunofluorescence study with laminin and fibronectin monoclonal antibodies on paraffin sections, as well as with serum from a patient with Goodpasture's syndrome with high titer of autoantibodies that recognize the antigenic determinants in human glomerular and tubular basement membrane, was performed on 14 patients with Alport's syndrome and 5 specimens of normal renal tissue obtained from donors in cases of renal transplantation (control group). We found no binding of Goodpasture antigen to glomerular and distal tubular basement membranes in renal biopsy tissue from all 14 patients with Alport's syndrome. In contrast, there was bright linear fluorescence of Goodpasture antigen on glomerular and tubular basement membranes of normal renal material. There was no difference in laminin and fibronectin binding in patients with Alport's syndrome and controls. In all the cases binding was strongly positive. These results suggest an abnormality or absence of immunoreactive autoantigen in the glomerular and distal tubular basement membrane in patients with Alport's syndrome. Therefore, Goodpasture antigen detection could be an important diagnostic method in early stages of Alport's syndrome when characteristic morphological changes are not yet developed.

Production of anti-NC1 antibody by affected male dogs with X-linked hereditary nephritis: a probe for assessing the NC1 domain of collagen type IV in dogs and humans with hereditary nephritis

Some patients with hereditary nephritis (HN) who have received a renal transplant have been shown to form antibody with specificity for the NC1 domain of collagen type IV, a major constituent of glomerular basement membranes (GBM). We attempted to duplicate this phenomenon in a family of dogs with X-linked HN, a model for human X-linked HN, by immunizing affected male dogs with normal dog NC1 domain. A collagenase digest was prepared from normal dog GBM, the NC1 domain was separated into dimer (approximately 50 kDa) and monomer (24 kDa and 26 kDa) components by SDS-PAGE, and injected into two affected male dogs. Antisera obtained from both dogs contained antibody which reacted with the NC1 domain of dog and human GBM by a plate-binding radioimmunoassay, bound to the dimer and 26 kDa monomer bands by Western blotting, and staining dog and human GBM by immunofluorescence (IF). The affected male dog antiserum reacted equally by radioimmunoassay with the NC1 domain isolated from GBM of unaffected, affected male, and carrier female dogs in the family with X-linked HN, and bound by Western blotting to dimers and the 26 kDa monomer band of the NC1 domain of GBM in each group of dogs. However, the affected male dog antiserum differentiated these dogs by IF; it produced global staining of GBM of unaffected dogs, failed to stain GBM of affected male dogs, and produced segmental staining of GBM of carrier female dogs. Absorption of the affected male dog antiserum with normal dog NC1 domain eliminated the staining of dog GBM by IF, whereas staining persisted after absorption with affected male dog NC1 domain. The abnormal staining patterns of GBM seen by IF in the affected male and carrier female dogs and the results of the absorption studies imply an abnormality of one or more determinants in the 26 kDa monomer band of the NC1 domain of their GBM. Amino acid sequencing of this band identified the alpha 1(IV) chain of collagen type IV, a finding that has implications for the pathogenesis of canine X-linked HN. Absent and segmental staining respectively were also seen by IF in GBM of a male and female patient with HN, using the affected male dog antiserum. Thus, the results obtained in affected male and carrier female dogs with X-linked HN may also be relevant to patients with this disease.

Different mutations in the COL4A5 collagen gene in two patients with different features of Alport syndrome

Alport syndrome is a hereditary renal disease in which progressive renal failure is often accompanied by sensorineural deafness and ocular abnormalities. Recently, mutations were detected in the type IV collagen alpha 5 chain gene in Alport syndrome patients. We searched for mutations in this gene in 18 unrelated patients, and in two patients abnormalities were detected. In the gene of patient BB we identified a complex deletion, which included the exons encoding the non-collagenous domain and part of the collagenous region. This patient showed early onset nephritis (end-stage renal disease at 17 years) with deafness. Within a year after receiving a kidney from an unrelated donor, he developed an antiglomerular basement membrane nephritis. In patient WJ a point-mutation was detected, changing a tryptophane into a serine in the non-collagenous domain. His clinical features are milder (renal failure at 33 years, no hearing loss), and a recent renal allograft did not provoke antiglomerular basement membrane disease. These initial data suggest that differences in the extent of disruption of the non-collagenous domain may correlate with the severity and/or heterogeneity of Alport syndrome and with the development of nephritis in renal allografts.

The pathogenesis of Alport syndrome involves type IV collagen molecules containing the alpha 3(IV) chain: evidence from anti-GBM nephritis after renal transplantation

Mutations in the COL4A5 collagen gene have been implicated as the primary defect in Alport syndrome, a heritable disorder characterized by sensorineural deafness and glomerulonephritis that progresses to end-stage renal failure. In the present study, the molecular nature of the defect in Alport glomerular basement membrane (GBM) was explored using anti-GBM alloantibodies (tissue-bound and circulating) produced in three Alport patients subsequent to renal transplantation. The alloantibodies bound to the alpha 3(IV)NC1 domain of type IV collagen and not to any other basement membrane component. In tissue sections, the alloantibodies bound specifically to peripheral GBM in normal kidney and the affected renal transplant but not to that of Alport kidney. These results establish that: the alpha 3 chain in type IV collagen molecules, the Goodpasture autoantigen, is the target alloantigen in post-transplant anti-GBM nephritis in patients with Alport syndrome, and that a molecular commonality exists in the pathogenesis of anti-GBM nephritis causing loss of renal allografts in patients with Alport syndrome and renal failure in patients with Goodpasture syndrome. These findings implicate: (1) defective assembly of type IV collagen molecules containing the alpha 3(IV) chain in Alport GBM; and (2) the existence of a mechanism linking the assembly of molecules containing the alpha 3(IV) chain with those containing the alpha 5(IV) chain.

Immunochemical studies of the Alport antigen

The Alport antigen, a component of normal glomerular basement membranes (GBM) which is absent in Alport familial nephritis, is characterized as a 26 kD non-collagenous (NC1) peptide identified by a monoclonal antibody (Mab A7) and an Alport alloantibody. Both antibodies discriminate X-linkage of the Alport defect using indirect immunofluorescence of hemizygous and heterozygous Alport GBM and epidermal basement membrane (EBM). Immunoblotting of SDS-PAGE gels of collagenase-digested Alport renal BM shows absence of monomeric and dimeric components of the Alport antigen, alpha 3(IV) NC1, and alpha 4(IV) NC1. By immunoprecipitation experiments with specific antibodies, the Alport antigen is distinct from the 26 kD NC1 peptide derived from alpha 1(IV). The monoclonal antibody to the Alport antigen and rabbit antiserum to a non-consensus sequence of alpha 5(IV) NC1 react similarly by immunofluorescence with normal kidney and both fail to bind to Alport renal BM. Two dimension Western blots of collagenase-digested BM show that the anti-Alport antigen and the ant-alpha 5(IV) NC1 react similarly with monomeric and dimeric components of BM collagen. These studies are consistent with the likelihood that the Alport antigen and alpha 5(IV) NC1 are the same or are highly homologous molecules. The precise relationship will require characterization of alpha 5(IV) NC1 protein and determination of the nucleotide sequence of the Alport antigen. The associated absence of alpha 3(IV) NC1 and alpha 4(IV) (NC1) from Alport BM is consistent with other observations for a molecular association of these chains in a novel collagen network.

Evidence for separate networks of classical and novel basement membrane collagen. Characterization of alpha 3(IV)-alport antigen heterodimer

The COOH-terminal non-collagenous domains (NC1) of type IV collagen from glomerular basement membranes (GBM), lens capsule basement membranes, and Descemet's membrane varied in the distribution of their NC1 subunits. All of these basement membranes (BMs) contained both classical (alpha 1(IV) and alpha 2(IV)) and novel collagen chains (alpha 3(IV), alpha 4(IV) and the Alport antigen). Whereas GBM had a predominance of disulfide-bonded subunits, the lens capsule and Descemet's membrane were primarily monomeric, differences that are likely related to the functional and structural diversity of collagen in various tissues. A heterodimer formed from monomeric subunits of alpha 3(IV) and the Alport antigen exists in human and bovine GBM. This dimer represents an important cross-link of the NC1 domain of novel collagen. Additionally, immunoaffinity methodology showed that the novel BM collagen hexamers segregate into populations containing only novel BM subunits without the participation of the classical subunits (alpha 1(IV) and alpha 2(IV)). These data provided evidence for the presence of two separate networks of BM collagen: one containing alpha 1(IV) and alpha 2(IV), and the other consisting of the novel collagen chains.