The Goodpasture antigen in Alport's syndrome: studies with a monoclonal antibody

Alport disease: a review of the diagnostic difficulties

In patients with familial hematuria, ultrastructural study of the renal biopsy has been the gold standard for the diagnosis of Alport disease, based on characteristic findings of glomerular basement membrane thickening due to reduplication of the lamina densa. But the diagnosis has difficulties as not all biopsies from Alport disease patients have these structural changes. In adult female patients or in children, extensive thinning of the basement membrane can be the major abnormality by electron microscopy. Until the genetic mutation of collagen IV responsible for Alport disease can be demonstrated in all patients, the diagnosis will continue to be a challenge at the clinical and at the ultrastructural levels.

Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes

Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.

X-linked Alport syndrome in females

Alport syndrome (AS) is in the differential diagnosis of hematuria. Variability in clinical presentation and in the ultrastructural changes of the glomerulus can make the diagnosis of AS a challenge in female patients. The purpose of this report is to present immunostaining for glomerular basement membrane (GBM) expression of alpha5(IV) as an adjunctive diagnostic method. Renal biopsy specimens from eight female patients with clinical presentation suggestive of AS were studied. The patients were between 7 and 36 years of age; six were between 12 and 15 years. Light microscopy and immunohistochemistry using a monoclonal antibody to alpha5(IV) were performed. Controls showed a continuous linear pattern along the GBM in normal kidneys and absence in renal biopsy specimens from male X-linked AS patients. To express the variability of the ultrastructural GBM changes among the patients in the series, we developed a semi-quantitative Alport Index, obtained by quantification of severity and extent of ultrastructural GBM changes. With immunohistochemistry, we showed an interrupted, discontinuous linear pattern for alpha5(IV) in glomeruli from the eight patients in the series, confirming the diagnosis of X-linked AS. The ultrastructural Alport Index varied between 6 and 47, showing the heterogeneity in the severity of the GBM changes, even among the six patients aged between 12 and 15 years. In three of the eight biopsy specimens, the predominant change was thin GBM, and the Alport Index was below 20. Immunohistochemistry for alpha5(IV) in renal biopsy specimens can identify female patients heterozygous for X-linked AS. In this series, the method led to the diagnosis of AS in female patients in whom the predominant ultrastructural change was thin basement membrane.

Basement membrane synthesis and degradation

The biological importance of complex interactions between cells and extracellular matrix has become widely recognized. For normal epithelial cells, contact with the matrix is limited to the basement membrane. Our understanding of the composition and assembly of basement membranes is increasing, as is our understanding of the mechanisms by which synthesis and degradation of basement membranes are controlled. Basement membrane abnormalities may result from disease and may cause disease. Papers in this edition of the Journal of Pathology discuss changes in basement membrane composition in disease, and add yet another link to the many connections between basement membranes, fibrosis and the control of cell proliferation.

Epitope mapping of homologous and cross-reactive antigens by monoclonal antibodies to streptococcal cell membrane (mAb to SCM)

An approach to epitope mapping of a series of anti-streptococcal cell membrane (SCM) mAbs is described. Evaluations by enzyme-linked immunosorbent assay (ELISA) of one control mAb HB-35 and 13 different anti-SCM mAbs were made on homologous SCM antigen and human basement membrane antigens isolated from glomeruli (GBM) and lung (LBM). These anti-SCM mAbs were previously shown to be cross-reactive in a variety of systems with both GBM and LBM. The binding capacities were measured for all 14 mAbs on ELISA plates sensitized with SCM antigen or the cross-reactive GBM or LBM antigens, at 5 micrograms/ml or approximately 20 pM/well. From the 50% binding capacity dilution the pM of mAb bound/pM antigen-well was calculated which translated into an estimate of the ratio-number of epitopes bound. Observations with the homologous and cross-reactive antigens showed multiple reactive epitope ratios to eight mAbs whereas the other five yielded a ratio value of one or two on the tested antigens. Plates blocked with a specific dilution of one mAb evaluated the binding by a second mAb providing both binding and specificity data. One mAb (I-F-3) blocked all the other anti-SCM mAbs on all three antigen plates. An additive effect was noted by three mAbs, I-G-8, II-C-4 and II-D-8 with most of the other mAbs. The order of placement, however, made distinctive differences; II-F-4 showed an additive or enhancement effect on I-B-5 but no reciprocal effect was seen. A similar effect was made with I-G-8 and II-C-4 or I-F-7. Possible interpretations are that each mAb is binding different epitopes each fully exposed, and the order of placement of the mAbs makes no difference. Where an enhanced effect was observed it is suggested that the binding of the first mAb changed the conformation of the antigen, thereby opening and exposing additional epitope(s) to the second antibody. Or, in contrast, where the second mAb was blocked by the first, a fixing of the protein conformation is suggested thereby occluding the other epitope, as seen with I-F-3 and II-C-4. These epitope mapping procedures confirmed that all 13 anti-SCM mAbs were binding at different epitopes. The nature of basement membrane collagens and how this relates to post-streptococcal sequelae will be discussed.

Immunohistochemical study of alpha 1-5 chains of type IV collagen in hereditary nephritis

The distribution of alpha 1-5 chains of type IV collagen [alpha 1-5(IV)] in the glomerular basement membrane (GBM) and epidermal basement membrane (EBM) of 23 families with hereditary nephritis was examined by indirect immunofluorescence. These families were divided into three clinicopathological groups. Group I (10 families) patients showed a widespread "basket weave" pattern of the GBM and a family history of nephritis was present. Group II (6 families) patients showed a widespread "basket weave" change without a family history of nephritis. Group III (7 families) patients showed a widespread attenuation of the GBM but no "basket weave" change, and had a family history of nephritis and chronic renal failure. alpha 1(IV) and alpha 2(IV) were present in all affected and unaffected family members and controls. All normal family members and controls expressed alpha 3(IV), alpha 4(IV) and alpha 5(IV) in the GBM and alpha 5(IV) in the EBM in a diffuse pattern. All group I families and three of the group II families exhibited complete loss of the alpha 5(IV) antigen from the GBM and EBM in male patients, and segmental loss of the alpha 5(IV) antigen in female patients. In these families the alpha 3(IV) and alpha 4(IV) antigens were completely lost from the GBM in male patients with severe nephritis, whereas alpha 3(IV) alpha 4(IV) were present but diminished in male patients with mild nephritis. Three group II and all group III families expressed the alpha 3-5(IV) antigens in an identical manner to that of normal controls. These findings indicate that the heterogeneity of hereditary nephritis reflects a variety of aberrant expression patterns of alpha 3-5(IV) and that immunohistochemical examination of alpha 5(IV) in the EBM is a useful method for the diagnosis of X-linked Alport syndrome.

Recurrent diseases in the kidney transplant

Virtually all diseases affecting the native kidney recur in the kidney transplant with the exception of Alport syndrome, polycystic kidney disease, hypertension, chronic pyelonephritis, and chronic interstitial nephritis. Fortunately, in the majority of patients, recurrence of the original disease has minimal clinical impact, with only approximately 5% of all graft loss occurring as a result of recurrent disease. The primary renal diseases that commonly recur include membranoproliferative glomerulonephritis type II, IgA nephropathy, and focal and segmental glomerular sclerosis. The most common systemic disease that recurs is diabetic nephropathy. Living-related transplantation should be used with caution in patients with the hemolytic uremic syndrome, recurrent focal and segmental glomerular sclerosis, and membraneous glomerulonephritis. Fabry disease and primary hyperoxaluria type I are no longer absolute contraindications to kidney transplantation.

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 syndrome: from bedside to genome to bedside

Alport syndrome is a genetic disorder of basement membranes manifested clinically by a progressive nephropathy and, in many families, sensorineural hearing loss and ocular lesions. During the 1980s evidence was amassed indicating type IV (basement membrane) collagen as the defective protein in Alport This hypothesis was confirmed in 1990 by the cloning of the X-chromosomal gene COL4A5, which encodes the alpha 5 chain of type IV collagen, and the discovery of mutations in this gene in many Alport kindreds. The results of results of recent studies suggest that the alpha 5(IV) chain forms a distinct collagenous network with the alpha 3 and alpha 4 chains of type IV collagen and that mutations in alpha 5(IV) may prevent the normal incorporation of alpha 3(IV) and alpha 4(IV) into basement membranes. Renal biopsy remains an important modality for making the diagnosis of Alport syndrome, but may eventually be replaced by molecular genetic techniques. Posttransplant anti-glomerular basement membrane nephritis occurs rarely in Alport patients and may be restricted to a subgroup with particular COL4A5 mutations. It is not clear why COL4A5 mutations result in glomerulosclerosis and renal failure, or whether this process may be slowed through dietary or pharmacologic intervention.

COL4A5 splice site mutation and alpha 5(IV) collagen mRNA in Alport syndrome

Mutations affecting the COL4A5 gene encoding the alpha 5 chain of type IV collagen, are involved in the pathogenesis of X-linked Alport syndrome. We used denaturing gradient gel electrophoresis (DGGE) to screen PCR amplified exons of COL4A5 for point mutations in a set of 18 Alport patients previously characterized by Southern blotting. One sequence variant was identified in the exon 38 region of a male Alport patient. Sequence analysis revealed a G to C transversion in the 5' intron splice donor site downstream from exon 38 (GT to CT). To determine the effect of the mutation on mRNA splicing, alpha 5(IV) cDNA was generated from total RNA of peripheral blood lymphocytes. Subsequent cDNA PCR yielded a product 81 base pairs shorter in the affected Alport patient, compared to normal controls. The absence of exon 38 from the alpha 5(IV) cDNA was confirmed by sequence analysis. The results demonstrated that the mutation leads to skipping of exon 38 in the processing of alpha 5(IV) pre-mRNA. The shortened transcript lacked 27 codons encoding a Gly-X-Y-repeat sequence with a preserved reading frame, enabling the translation of codons further downstream. Clinically, the patient presented with juvenile onset Alport syndrome, end-stage renal failure, and deafness. He had no ocular lesions. Typical ultrastructural changes of the glomerular basement membrane (GBM) were shown on electron microscopy. The patient developed anti-GBM antibodies after renal transplantation, however, renal function deteriorated only moderately.

Deletions of the COL4A5 gene in patients with Alport syndrome

Mutations in the COL4A5 gene encoding the alpha 5 chain of type IV collagen have been found in linkage with X-chromosomal Alport syndrome (AS). To identify COL4A5 mutations in patients from Germany with clinically defined AS, DNA from 20 unrelated patients was analyzed by conventional Southern blotting. By using full length alpha 5(IV) cDNA probes, large COL4A5 deletions could be detected in two patients. In one case, a 34 kb deletion affecting the 14 most 3' exons of the gene was observed. The second patient harbored a complete COL4A5 deletion. In both cases, functional alpha 5(IV) mRNA was unlikely to be present. Clinically, both patients developed end-stage renal failure before age 30. Furthermore, they had characteristic retinal flecks, and sensorineural hearing loss with typical changes on the audiogram. The patient with the complete deletion of COL4A5 lost the renal allograft due to an anti-GBM mediated glomerulonephritis.

Intraglomerular pressure and mesangial stretching stimulate extracellular matrix formation in the rat

To define the interplay of glomerular hypertension and hypertrophy with mesangial extracellular matrix (ECM) deposition, we examined the effects of glomerular capillary distention and mesangial cell stretching on ECM synthesis. The volume of microdissected rat glomeruli (Vg), perfused ex vivo at increasing flows, was quantified and related to the proximal intraglomerular pressure (PIP). Glomerular compliance, expressed as the slope of the positive linear relationship between PIP and Vg was 7.68 x 10(3) microns 3/mmHg. Total Vg increment (PIP 0-150 mmHg) was 1.162 x 10(6) microns 3 or 61% (n = 13). A 16% increase in Vg was obtained over the PIP range equivalent to the pathophysiological limits of mean transcapillary pressure difference. A similar effect of renal perfusion on Vg was also noted histologically in tissue from kidneys perfused/fixed in vivo. Cultured mesangial cells undergoing cyclic stretching increased their synthesis of protein, total collagen, and key components of ECM (collagen IV, collagen I, laminin, fibronectin). Synthetic rates were stimulated by cell growth and the degree of stretching. These results suggest that capillary expansion and stretching of mesangial cells by glomerular hypertension provokes increased ECM production which is accentuated by cell growth and glomerular hypertrophy. Mesangial expansion and glomerulosclerosis might result from this interplay of mechanical and metabolic forces.

Distribution of the alpha 1 and alpha 2 chains of collagen IV and of collagens V and VI in Alport syndrome

We compared the distribution of the alpha 1 and alpha 2 chains of collagen IV and of collagens V and VI in glomeruli of males with Alport syndrome to their distribution in normal glomeruli and glomeruli from patients with non-Alport renal diseases. alpha 1(IV), alpha 2(IV), collagen V and collagen VI are normally restricted to the mesangium and the subendothelial aspect of the glomerular basement membrane (GBM). In contrast, these proteins were present throughout the entire width of the GBM in Alport glomeruli. These alterations were apparent in "early" Alport glomeruli, that is, those exhibiting minimal abnormalities by light microscopy, and they were further accentuated in sclerosing Alport glomeruli. Obsolescent Alport glomeruli, in which the capillary tuft had collapsed and few remaining cell nuclei were present, exhibited nearly complete loss of alpha 1(IV) and alpha 2(IV), like obsolescent glomeruli in non-Alport diseased kidneys. However, the matrix of obsolescent Alport glomeruli stained intensely for collagen V and collagen VI, while these collagen types were not prominent in obsolescent glomeruli of non-Alport diseases kidneys. These observations suggest that the process of glomerulosclerosis in Alport kidneys has attributes unique to this disease. It would also appear that mutations affecting the Alport gene product have secondary effects on the distribution of other GBM constituents.

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.

Molecular cloning of the human Goodpasture antigen demonstrates it to be the alpha 3 chain of type IV collagen

To characterize the autoantigen of Goodpasture's (anti-glomerular basement membrane) disease, a molecule of 26-kD reactive with autoantibodies from patients' sera was purified from collagenase digests of sheep glomerular basement membrane. Short internal amino acid sequences were obtained after tryptic or cyanogen bromide cleavage, and used to deduce redundant oligonucleotides for use in the polymerase chain reaction on cDNA derived from sheep renal cortex. Molecules of 175 bp were amplified and found to come from two cDNA sequences. One was identical to that of a type IV collagen chain (alpha 5) cloned from human placenta and shown to be expressed in human kidney. The other was from a type IV collagen chain with close similarities to alpha 1 and alpha 5 chains, and was used to obtain human cDNA sequences by cDNA library screening and by further polymerase chain reaction amplifications. The correspondence of the derived amino acid sequence of the new chain with published protein and cDNA sequences shows it to be the alpha 3 chain of type IV collagen. Its gene, COL4A3, maps to 2q36-2q37. The primary sequence and other characteristics of this chain confirm that it carries the Goodpasture antigen.

Restricted specificity of the autoantibody response in Goodpasture's syndrome demonstrated by two-dimensional western blotting

The autoantigen in Goodpasture's syndrome is known to be contained within the non-collagenous (NC1) domain of type IV collagen. We have examined the specificity of autoantibodies to glomerular basement membrane (GBM) using the technique of 2-D electrophoresis followed by Western blotting. Protein stains of 2-D gels of collagenase-digested human GBM revealed extensive charge and size heterogeneity. Major components were of mol. wt 24-30 kD and 43-56 kD, corresponding to monomeric and dimeric subunits of NCl. Western blotting of 2-D gels with IgG from patients with anti-GBM disease demonstrated that the most antigenic components migrated as cationic 28-kD monomers (pI 10) and similarly charged dimers, although other components were recognized less strongly. The mobility of the strongly antigenic polypeptides was different to that of the known alpha 1 and alpha 2 chains of type IV collagen. Autoantibodies from all 20 patients studied showed the same pattern of reactivity, regardless of their clinical features (in particular, the presence or absence of pulmonary haemorrhage) or HLA type. A monoclonal antibody (P1) to human GBM bound in a similar pattern, particularly recognizing the cationic components. 2-D gels of affinity-purified GBM from a P1 column showed enrichment of the 28-kD monomers, which were recognized by human autoantibodies on Western blotting. These results demonstrate that the autoimmune response in Goodpasture's syndrome is of restricted specificity, and support the suggestion that the major autoantigenic determinant is present on the novel alpha 3 chain of type IV collagen.

The gene corresponding to the putative Goodpasture antigen is present in Alport's syndrome

Alport's syndrome is a heterogeneous group of inherited abnormalities of basement membranes that may result in progressive renal failure, defective hearing and lens abnormalities. The glomerular basement membrane (GBM) characteristically has areas of reduplication, lamellation and attenuation on electron microscopic examination. In the majority of affected males and some females, there is reduced or variable binding of serum from patients with anti-GBM disease (Goodpasture's syndrome) to these basement membranes. These sera contain antibodies directed against the Goodpasture antigen which has been thought to be located in the non-collagenous domain of the alpha3 chain of type IV collagen and is presumed to be important in cross-linking of the collagen molecules. The reduced staining for the Goodpasture antigen suggests that this structure is either absent or masked in Alport's syndrome. We have tested DNA from six unrelated individuals with Alport's syndrome. All had been transplanted for renal failure. The diagnosis of Alport's syndrome was made on the characteristic electron microscopic appearance of the renal basement membranes (n = 4), the presence of sensori-neural deafness (n = 4), a family history of Alport's syndrome (n = 5) and the presence of circulating inhibitable anti-GBM antibody activity post-transplant (n = 2). Oligonucleotides (20mers) corresponding to the 5' and 3' ends of the known 25 amino acid sequence for the putative Goodpasture antigen were used as primers for amplification of genomic DNA. The products were then blotted and probed with an intermediate 19-mer DNA. All Alport's patients contained a 75-bp fragment corresponding to the published peptide sequence for the non-collagenous domain of the alpha 3 chain of type IV collagen, suggesting that a large deletion of this region, the putative Goodpasture antigen, is unlikely to account for the defect in Alport's syndrome.

Recurrent corneal epithelial erosions in Alport's syndrome

Alport's syndrome is a heritable disorder of uncertain aetiology characterized by nephritis, sensorineural deafness and ocular abnormalities. Bilateral corneal epithelial erosions are a previously unreported finding which support the hypothesis that Alport's syndrome is a disorder of selected basement membranes.

Hybridomas to specific streptococcal antigen induce tissue pathology in vivo; autoimmune mechanisms for post-streptococcal sequelae

A gross examination of organs from approximately 100 mice which were producing ascites fluids toward a series of streptococcal reactive monoclonal hybridomas showed, in some animals, what appeared to be autoimmune-like findings. A pattern of major lung pathology was associated with specific clones. These specific hybridomas led to the development of an experimental autoimmune animal model mimicking a Goodpasture's syndrome. Tissue injury was induced in mice, on a dose dependent basis, by the injection of monoclonal antibody generated against streptococcal cell membrane (SCM) antigens. A more severe onset of the pathology, also on a dose dependent bases, was induced by placement of the anti-SCM mAb secreting hybridoma cells into the peritoneal cavity of the host. Severity of observed lesions was dependent upon the number of cells injected (10(5), 5 x 10(5), 10(6) or 10(7], as well as the animals' sex. Severe and total hemorrhagic lungs were seen in animals challenged with 1 x 10(6) hybridomas cells when sacrificed on the tenth day. In all cases the lesions were greater in the female litter mate than the male. Gross and histologic observations were confirmed by lung/body weight ratios. Pulmonary hemorrhage ranged from slight, when mAb was injected at a low dose of 24 micrograms/g, to severe when 96 micrograms/g was injected. Reported findings were based on the review of approximately 300 mice. Immunochemical evaluations and ELISAs confirmed the ability of these anti-SCM mAb to react with glomerular basement membrane (GBM) antigens as well as lung basement membrane (LBM). Mitogenic experiments indicated that the parent immunogen (SCM) used to generate immunocytes was non-stimulatory to lymphocytes.

Deduction from Wilms' tumour that glomerular podocytes produce the basement membrane material bearing Goodpasture determinants

Using an indirect immunoperoxidase technique, we tested frozen specimens from one Wilms' tumour composed of numerous glomeruloid bodies devoid of blood vessels, with monoclonal antibodies directed against vimentin, cytokeratin, CALLA/CD10, CD24, CR1/CD35, endothelium factor VIII, class I and II MHC molecules, laminin, fibronectin, and non-collagenic domain NC1 of type IV collagen. Two reagents against Goodpasture determinants were used: P1 monoclonal antibody and serum IgG (GP antibodies) from a biopsy-proven Goodpasture patient. Glomeruloid bodies comprised two cell types: a peripheral layer of parietal epithelial cells (cytokeratin and CD24-positive) and central cell clumps of podocytes (vimentin and CALLA-positive). The basal lamina surrounding the glomeruloid bodies contained laminin and NC1 domain of type IV collagen, while that present between the podocytes reacted strongly with laminin, and P1 and GP antibodies. Endothelium factor VIII was not detected within the glomeruloid bodies and CR1 molecules bound to the basement membrane material within them. These data favour the hypothesis that podocytes produce the basement membrane material which bears Goodpasture determinants recently identified as a novel chain, named the alpha 3 chain, of type IV collagen.

Gene mapping in Alport families with different basement membrane antigenic phenotypes

The present study was undertaken to determine whether differences among Alport kindreds in the antigenic phenotypes of their basement membranes result from defects at distinct genetic loci or from allelic mutations at a single locus. We analyzed linkage of the Alport gene to polymorphic loci on the X chromosome in three families with Alport syndrome. In two of the families, epidermal basement membranes of affected members showed altered immunohistologic reactivity with a discriminating antibody (FNS1) that identified a 26 kD peptide in the NCl domain of basement membrane collagen. In the third family epidermal basement membranes of affected individuals reacted normally with the antibody. The disease gene mapped to the Xq21-q22 region of the long arm of the X chromosome in the two families with altered basement membrane antigenicity and in the family with normal basement membrane antigens. We conclude that Alport syndrome in each of these kindreds arose from allelic mutations at a single genetic locus, although we cannot at this time exclude the possibility that two or more tightly linked genes are involved. As the genes for the known chains of type IV collagen are on chromosome 13, our findings suggest that the Alport gene may encode a new basement membrane collagen chain.

Alport syndrome, basement membranes and collagen

Alport syndrome, an inherited disorder of the kidney, eye and ear, has fascinated nephrologists, pathologists, and geneticists for nearly a century. With the recent application of molecular biochemical and genetic techniques, this mysterious disease has begun to yield some of its secrets. Alport syndrome can now be viewed as a generalized disorder of basement membranes that appears to result from mutations in an X-chromosome-encoded basement membrane collagen chain. This chain, along with two other novel collagen chains, is absent from Alport basement membranes, in contrast to the classical chains of collagen IV. Phenotypic heterogeneity in Alport syndrome probably arises from allelic mutations at a single genetic locus. The phenomenon of post-transplant anti-glomerular basement membrane nephritis may be a manifestation of specific mutations at the Alport locus that prevent synthesis of the gene's protein product and the establishment of immunological tolerance.

Correlation of glomerular basement membrane alterations with clinical data in progressive hereditary nephritis (Alport's syndrome)

Electron microscopic examination of glomerular basement membrane (GBM) was performed in 19 patients whose morphological changes as well as clinical features indicated the diagnosis of progressive hereditary nephritis (Alport's syndrome). The percentage of characteristically thickened and split and of thin GBM portions was determined in all the cases. The clinical course was more severe in males, which corresponded to higher rate of GBM alterations. In males, 58% of GBM was thickened and split and 24% was thin, while in females, the reverse was true, 28% was split and 48% of GBM was thin. There was a positive correlation of the split lesions and age in males, but not in females. The degree of splitting was directly proportional to the grade of proteinuria, while GBM thinning did not significantly correlate with proteinuria.

Failure of two subsequent renal grafts by anti-GBM glomerulonephritis in Alport's syndrome: case report and review of the literature

We describe a patient with Alport's syndrome who developed severe crescentic glomerulonephritis after each of two successive transplantations, leading to accelerated graft failure on both occasions. This complication occurred in the 7th postoperative month for the first transplant and in the immediate postoperative period for the second. Immunopathological studies of the second transplant demonstrated that the glomerular lesions were mediated by antiglomerular basement membrane (GBM) antibodies displaying the same pattern of reactivity as the MCA-Pl monoclonal antibody directed against the Good-pasture antigen. This observation indicates that the anti-GBM immunization induced by renal transplantation in some patients with Alport's syndrome may be responsible for recurrent graft failure.

Renal biopsy and family studies in 65 children with isolated hematuria

We have investigated 65 children with isolated hematuria persisting for at least a year. Renal biopsy specimens were studied by light microscopy, electron microscopy and immunofluorescence with antisera specific against basement membrane components. The majority of the biopsies (62/65) showed variable histologic abnormalities. Four categories could be distinguished on combined histological and clinical criteria: Alport syndrome (n = 8), benign hematuria (n = 33, familial in 23), IgA nephropathy (n = 16) and increase in mesangial cells and matrix (n = 5). On the basis of our results, we suggest that a renal biopsy can establish diagnosis and prognosis in those children with isolated hematuria where the family history is negative. If the family has adult male individuals with isolated hematuria, a biopsy can usually be avoided, since this family history effectively excludes Alport syndrome. The use of antisera against basement membrane components did not allow a differentiation between Alport syndrome and benign hematuria. Goodpasture serum immunofluorescence was variable in the former and normally present in the latter.

A study by immunofluorescence microscopy of the NC1 domain of collagen type IV in glomerular basement membranes of two patients with hereditary nephritis

The NC1 domain of the collagen type IV molecule, the major component of glomerular basement membranes (GBM), consists of dimers and 24 kilodalton (K), 26 K and 28 K monomers in man, and contains the Goodpasture antigen. Serum obtained from patients with Goodpasture's syndrome has been reported not to stain GBM of most male and some female patients with hereditary nephritis (HN) by immunofluorescence (IF) microscopy. In the present study, GBM seen on the renal biopsies of 2 patients (one male and one female) with HN were examined by IF to ascertain whether NC1 monomers were detectable. Three reagents were used: a plasmapheresis fluid (PPF) obtained from a patient who was treated for anti-GBM nephritis (human anti-GBM PPF); a commercial rabbit antibody against human NC1; and a rabbit antibody raised by us against dog NC1, which cross-reacted with human NC1. All 3 reagents detected NC1 determinants in GBM of normal human kidney by IF and reacted with human NC1 by a plate-binding radioimmunoassay (RIA). The human anti-GBM PPF bound to 28 K and 26 K monomer components of NC1 by Western blotting, the rabbit anti-human NC1 antibody bound to 26 K and 24 K monomers, while the rabbit anti-dog NC1 antibody bound only to the 26 K monomer. By IF, the human anti-GBM PPF did not stain GBM of the male patient with HN, but produced segmental staining of GBM (i.e., some GBM stained, while others did not) of the female patient. In contrast, the rabbit anti-NC1 antibodies produced global staining by IF of GBM of both patients. The absence of staining (i.e., global or segmental) seen with the human anti-GBM PPF implied that the 26 K and 28 K monomers of NC1 were either absent from GBM, or were present but altered structurally, leading to a diminution in their immunological reactivity. However, the positive staining observed with the rabbit anti-NC1 antibodies implied that the 26 K monomer was actually present in GBM. Hence, we postulate that the 26 K monomer of NC1 in GBM was structurally altered, and that the 28 K monomer was either absent, or present but altered. These findings suggest that there is an abnormality of more than one monomer of NC1 in GBM of patients with HN.

Identification of variant Alport phenotypes using an Alport-specific antibody probe

An antibody, which recognizes an epitope(s) on a 26 kD peptide of the noncollagenous domain of type IV collagen and which fails to bind to basement membranes of individuals with Alport syndrome, was used to characterize members of families representing phenotypic variants of the disorder. Ten of 11 families with juvenile-onset renal failure and 4 of 5 families with adult-onset renal failure exhibited loss of the epitope(s) from epidermal and/or renal basement membranes by indirect immunofluorescence. Two families with typical Alport nephropathy but normal hearing exhibited the same abnormality. This study provides strong evidence that a defect in the main noncollagenous domain of type IV collagen is common to the various phenotypes of Alport syndrome.

The development of anti-glomerular basement membrane nephritis in two children with Alport's syndrome after renal transplantation: characterization of the antibody target

Two children with Alport's syndrome are described, who developed anti-glomerular basement membrane (GMB) antibody-mediated nephritis after renal transplantation. The reactivity of antibodies in their serum with collagenase-solubilized normal GBM was examined by SDS-PAGE with one- and two-dimensional immunoblotting. The specificity was compared with that of antibodies present in serum from a patient with Goodpasture's syndrome, and a mouse monoclonal antibody (MCA-P1), directed against the Goodpasture antigen. All reacted in a similar way with collagenase-solubilized GBM. Since abnormalities in the composition of the GBM are present in Alport's syndrome, it is proposed that differing antigen composition of GBM in the host compared with the donor kidney, together with transplant rejection, may have provoked the development of post-transplant anti-GBM antibodies.

Thin-basement-membrane nephropathy in adults with persistent hematuria

Thin-basement-membrane nephropathy, also called benign recurrent hematuria, is characterized by diffuse thinning of the glomerular basement membrane and by hematuria. To determine the incidence of thin-basement-membrane nephropathy among patients with idiopathic hematuria, we conducted a prospective study in the nephrology units of three large hospitals in the Netherlands. Eighty normotensive adults without azotemia underwent renal biopsy because of recurrent macroscopic hematuria (n = 26) or persistent microscopic hematuria (n = 54). Idiopathic IgA nephropathy was found in 27 of the 80 patients. Light microscopical examination showed that 42 patients had normal renal tissue. The remaining 11 patients had mesangioproliferative glomerulonephritis (n = 5), interstitial nephritis (n = 3), or focal global glomerulosclerosis (n = 3). Tissue from the 42 patients whose renal biopsy specimens were normal when examined with light microscopy was analyzed morphometrically with electron microscopy to determine the thickness of the glomerular basement membrane. Two subsets of patients were identified by this analysis. In 18, thin-basement-membrane nephropathy was found (mean basement-membrane thickness [+/- SE], 191 +/- 28 nm; normal, 350 +/- 43 nm); all but one of these 18 patients had microscopic hematuria, which persisted during follow-up (median duration, 50 months). (Of the 54 patients who presented with microscopic hematuria, 17 [31 percent] had thin-basement-membrane nephropathy.) The thickness of the glomerular basement membrane was normal in the other 24 patients (361 +/- 69 nm); during follow-up, hematuria disappeared in all 13 of these patients who had macroscopic hematuria, and hematuria resolved in 5 of the 11 patients who had microscopic hematuria. We conclude that in patients with persistent microscopic hematuria, the incidence of thin-basement-membrane nephropathy is similar to that of idiopathic IgA nephropathy. Morphometric analysis of the thickness of the glomerular basement membrane should be included in the workup of adults with persistent microscopic hematuria that is not of urologic origin.

Extraglomerular distribution of immunoreactive Goodpasture antigen

The distribution of Goodpasture antigen (GA) was studied in a range of human tissues using indirect immunofluorescence and immunoperoxidase techniques. Frozen sections were stained using (1) a mouse monoclonal antibody (P1) raised against the autoantigenic component of human glomerular basement membrane, (2) autoantibodies eluted from the kidneys of patients with Goodpasture's syndrome, (3) antibodies eluted from the kidneys of a sheep with Steblay nephritis, and (4) mouse monoclonal and guinea pig polyclonal antibodies to human type IV collagen. The same pattern of staining was demonstrated using the eluted antibodies and monoclonal antibody P1. The presence of GA was confirmed in the lung and choroid plexus. GA was also detected in basement membranes at a number of previously unreported sites in the eye, thyroid, pituitary, adrenal, breast, and liver. GA was absent from other sites at which type IV collagen could be demonstrated. Direct immunofluorescence studies of tissue from a patient with Goodpasture's syndrome revealed deposition of IgG in the choroid plexus and eye, as well as in the kidney and lung.

An immunohistochemical and electron microscopic study of extra-renal basement membranes in dogs with Samoyed hereditary glomerulopathy

Samoyed hereditary glomerulopathy (SHG) in dogs has been employed as a model for human hereditary nephritis (HN), since affected dogs and patients show splitting of glomerular capillary basement membranes by electron microscopy (EM) and absent staining of glomerular capillaries for Goodpasture antigen (GPA) by immunofluorescence (IF). EM and IF were used to examine basement membranes (BM) in skin, lung, choroid plexus, lens, retina, and inner ear in SHG. By EM, BM in these tissues appeared similar in affected male, carrier female, and unaffected dogs. By IF, GPA could be detected only in lens capsule, internal limiting membrane of retina and basilar membrane of inner ear of unaffected and carrier female dogs, but not in affected male dogs. However, eye abnormalities and hearing loss were not present in any dogs, in contrast to their frequent occurrence in human HN. Our findings on extra-renal BM in SHG suggest that GPA is not required to maintain normal vision or hearing in affected male dogs and permit a greater understanding of the pathogenesis of human HN.

The glomerular basement membrane abnormality in Alport's syndrome

The characteristic electron microscopic abnormality in Alport's syndrome is thickening of the glomerular basement membrane with splitting and lamellation of the lamina densa. It is commonly accompanied by severe attenuation of the basement membrane and sometimes by disruption of capillary walls. The ultrastructural abnormality is secondary to a more basic defect in the chemical structure of the glomerular basement membrane. Clues to chemical abnormalities have come from immunochemical studies, which suggest a lack of or alteration in that part of the noncollagenous portion of type 4 collagen related to Goodpasture antigen. Variability in the results of immunochemical studies suggest biochemical heterogeneity that still needs to be correlated with the known evidence of genetic heterogeneity in Alport's syndrome.

Glomerular lesions in the transplanted kidney in children

The glomerular pathology of 634 transplant specimens (526 biopsies and 108 transplantectomies) from 410 children was studied. Three types of glomerulopathies were observed: (1) recurrent glomerulonephritis (GN) (40 of 142 patients with glomerular nephropathy), (2) de novo GN (52 grafts), and (3) transplant glomerulopathy (29 grafts). The study of recurrent GN is considered of great interest because of the possible insight into the nature of the original disease and the opportunity to observe the evolution of the disease in sequential biopsies of the transplant. The two major forms of de novo GN were membranous GN and IgG linear deposits along glomerular and tubular basement membranes. Transplant glomerulopathy, although distinctive morphologically, may resemble membranoproliferative GN (MPGN) or thrombotic microangiopathy.

Alport's syndrome: specificity and pathogenesis of glomerular basement membrane alterations

In Alport's syndrome (AS) thinning and splitting of the glomerular basement membrane (GBM) are assumed to be characteristic ultrastructural alterations. Both lesions are, however, non-specific because they can occur in other glomerulopathies. In addition, splitting may be found in non-glomerular structures. It should be emphasized that the characteristic lesion in AS is a result of the widespread combination of thin and split GBM in the same biopsy specimen. In our opinion the basic lesion is the thin GBM, which is characterized by a lamina densa (measuring 50-150 nm in thickness) which may begin to split as a result of focal detachment of podocyte pedicles (spacing) and repeated subepithelial deposition of new lamina densa layers. Splitting thus appears to be a secondary lesion. Thinning of GBM may represent a persistent embryonal status of the lamina densa and may thus be the result of a development defect. This assumption is supported by the findings of fetal-like glomeruli and small capillary loops in AS.

Variants of Alport's syndrome

Variants of Alport's syndrome include mainly those associated with hereditary macrothrombocytopenia (and occasionally leukocyte inclusions) or with esophageal, tracheobronchial and genital leiomyomatosis. Within Alport's syndrome there appears to be no justification for differentiating those with nephritis and deafness from those with nephritis alone. However, in indirect immunofluorescence studies using the mouse monoclonal antibody, MCA-P1, which recognizes the glomerular basement membrane (GBM), reduced or absent binding was found in 20 of 42 cases of hereditary nephritis. Most of these showed typical ultrastructural GMB changes. These results suggest that there is probably a subset of patients characterized by typical GBM lesions and an absence, inaccessibility or abnormality of the GBM antigen recognized by MCA-P1.