Characterisation of human glomerular basement membrane antigenic fractions isolated by affinity chromatography utilising anti-glomerular basement membrane autoantibodies

Abnormalities in the NC1 domain of collagen type IV in GBM in canine hereditary nephritis

Samoyed hereditary glomerulopathy (SHG) in dogs serves as a model for human X-linked hereditary nephritis (HN). We previously showed that glomerular capillaries of affected males did not stain by immunofluorescence (IF) using serum from a patient with Goodpasture's syndrome. Our goal in the present study was to determine whether the NC1 domain of the collagen type IV molecule, which contains Goodpasture antigen (GPA), could be demonstrated in these dogs, and to assess its immunological reactivity. By SDS-PAGE, NC1 in collagenase digests of glomerular basement membranes (GBM) of unaffected and carrier female dogs in the family with SHG showed 24 kilodalton (kD), 26 kD and 28 kD monomer, and 46 kD and 47 kD dimer components, but the 24 kD monomer was diminished in the affected males. By IF, a rabbit antibody to NCl stained glomerular capillaries of unaffected, affected male, and carrier female dogs. In contrast, a human anti-GBM plasmapheresis fluid (PPF) stained glomerular capillaries of only the unaffected and carrier female dogs. By RIA, both antibodies reacted strongly with NCl in collagenase digests of GBM of the unaffected and carrier female dogs, but showed reduced reactivity with NCl of affected males. By Western blotting, both antibodies bound to dimers and 24 kD and 26 kD monomers of the NCl domain in collagenase digests of GBM of unaffected and carrier female dogs. However, in affected males, the rabbit anti-NCl antibody did not bind to the 24 kD monomer, while the human anti-GBM PPF showed weak binding to the 24 kD and 26 kD monomers.(ABSTRACT TRUNCATED AT 250 WORDS)

Ex vivo perfusion of plasma over protein A columns in human mammary adenocarcinoma. Evidence for a protein A leaking by radioimmunoassay

A solid phase radioimmunoassay (RIA) has been developed for detection of protein A in human serum or plasma using plates coated with specific goat anti-protein A IgG and affinity-purified anti-protein A F (ab')2 fragments labelled with 125Iodine as a tracer. This RIA detected 25 ng of protein A per ml of serum or plasma. The 'intra-plate' coefficient of variation (CV) was 4.26%, whereas the 'inter-plate' CV was 5.86%, even in the presence of aggregated IgG. The presence of protein A was searched for by this RIA in samples collected during ex vivo perfusion of the plasma of patients suffering from a metastatic mammary adenocarcinoma either over columns of 'native' protein A (seven patients; group A) or over columns of protein A in which the Fc-binding capacity was destroyed (five patients; group B). A protein A leaking occurred with the same incidence (about 20% of the sessions) in both groups. However, major acute side effects (hypotension, chills, mild fever, etc.) and necrolytic responses were seen only in some patients from group A. In these cases, the incidence of side effects, but not of tumoricidal responses, increased with the protein A serum concentrations reached 1 h after the end of the sessions (25-150 ng ml-1). The data suggest that the therapeutic efficacy of ex vivo protein A immunoadsorption in breast cancer is related to the Fc-binding capacity of the columns rather than to a leakage of 'native' protein A into the blood stream.

The involvement of type IV collagen in Goodpasture's syndrome

Goodpasture's syndrome, involving lung and kidney, is considered to be caused by autoantibodies to basement membranes. This paper has described the isolation and identification of the antigen, which is isolated from collagenase digests of glomerular basement membrane, as a monomer protein of 26,000 daltons and two dimers of about 50,000 daltons. Further analyses indicated that the antigenic protein is derived from the globular domain of type IV collagen corresponding to the NCl peptide. All 22 patients with Goodpasture's syndrome studied had circulating antibodies to this antigen, a few had additional antibodies to laminin, and only one also had antibodies to the 7S collagen domain. No other patient with glomerulonephritis had circulating antibodies to the antigen. The isolated protein can therefore be used in an assay specific for Goodpasture's syndrome. Interestingly the protein antigen could be identified in glomerular, lung, and placenta basement membranes, although the components reacting with the antibodies represented different proportions of the preparations.

Antiglomerular basement membrane antibodies in human sera: detection by a modified micro-ELISA

An enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to human glomerular basement membrane has been developed. Special emphasis has been put on the choice of microtiter plates which were coated with a collagenase digest of human glomerular basement membrane. Results differed markedly between the different microtiter plates. Best results were obtained with a flexible polyvinylchloride microtiter plate with flat wells (Dynatec). This plate exhibited the highest positive/negative ratio and the lowest intraassay standard deviation. Optimal conditions for each step in the ELISA have been determined. The assay proved to be specific, sensitive, and reproducible. Circulating antibodies in each of 11 patients with active antiglomerular basement membrane disease were detected by the ELISA, while sera from patients with various renal and nonrenal diseases were negative by the test.

Isolation and characterization of nephritogenic antigen from bovine glomerular basement membrane

A method for isolation of a potent nephritogenic antigen from bovine glomerular basement membrane has been established; the glomerular basement membrane was solubilized by trypsin digestion and fractionated successively by gel filtration on Ultrogel AcA-34, concanavalin A affinity chromatography and affinity chromatography on immobilized antibodies. The antigen thus prepared was found to be highly nephritogenic; it causes glomerulonephritis in rats by a single injection of 0.1 mg per individual. Amino acid and carbohydrate analyses revealed that the antigen is a glycoprotein which contains amino acids and sugars characteristic of collagen, namely, hydroxyproline, hydroxylysine, glycine, glucose and galactose, although the relative amounts of these amino acids and sugars are less than those found in Type IV collagen of glomerular basement membrane.

Isolation of the specific glomerular basement membrane antigen involved in Goodpasture syndrome

The antigen involved in the glomerulonephritis associated with antibodies to glomerular basement membrane (GBM) was purified from human GBM digested with highly purified clostridial collagenase. The purified nonreduced sample contained two components with closely similar mobilities on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. After reduction they moved as one, nonantigenic, component, corresponding to a molecular weight of 26,000. Immunologically identical aggregates of higher molecular weight (i.e., 48,000) were also identified in the crude digest. Reduction of such aggregates after purification released some protein with a molecular weight of 26,000, but a large proportion was insensitive to reduction. Seven patients with Goodpasture syndrome all had circulating anti-GBM antibodies directed only against the purified antigen.