Immunochemical characterization and quantitation of the human glomerular basement membrane antigen from the urine of patients with glomerular diseases.

A soluble glomerular basement membrane (GBM) antigen was detected in the urines of patients with various glomerular diseases including chronic glomerulonephritis, nephrotic syndrome, chronic renal insufficiency, and lupus nephropathy. The urinary GBM antigen (u-GBM) was immunochemically distinct from other renal antigens and other serum components, but it was cross-reactive with trypsinized human GBM antigen (t-GBM). The molecular size of u-GBM was approximately the same as human serum albumin as estimated by elution patterns on Sephadex G-200. The concentration of u-GBM was estimated quantitatively by a single radial radioimmunodiffusion. Although differed from case to case, a rough correlation with the type and/or stage of nephrotic syndrom existed. It was also demonstrated that the amounts of u-GBM decreased in response to steroid therapy of nephrotic syndrome. It was further shown that in a case of membranoproliferative glomerulonephritis, anti-GBM antibody could be eluted from the kidney removed from the patient. These findings imply that the GBM antigen plays an important role in the pathogenesis of human renal diseases. The pathophysiological significance of urinary GBM excretion in renal diseases is also discussed here.