PHYSICOCHEMICAL CHARACTERISTICS OF GLOMERULAR BASEMENT-MEMBRANE ANTIGENS IN URINE

Glomerular basment membrane (GBM) antigens in pooled normal urine and the pooled urine of infants with congenital nephrotic syndrome of Finnish type (CNF) have been characterized by gel filtration, ion-exchange chromatography, and immunodiffusion or immunoelectrophoretic analysis. Gel filtration studies were also done on urine samples from 7 individual children with various renal diseases. Using a single antiserum, we found four GBM antigens (Ag 1, 2, 3, and 4) in normal urine. Ag1 consistently produced the strongest precipitation in immunodiffusion analyses and was shown to be heterogeneous with respect to both molecular size (average mol wt, 100,000 daltons) and charge. In contrast, Ag3 gave the most intense precipitation in immunodiffusion analyses of urine concentrates from patients with CNF, diffuse mesangial sclerosis, and Alport's syndrome. Ag3 in these urine concentrates had an average mol wt of 40,000 daltons, somewhat smaller than that of Ag3 in normal urine. Ag1 was the only antigen to be detected in the urine of patients with steroid-sensitive nephrotic syndrome or focal glomerular sclerosis. In ion-exchange chromatography, Ag2 and Ag3 of CNF urine eluted at lower ionic strength than did the same antigens in normal urine, suggesting qualitative as well as quantitative differences. The observed heterogeneity of GBM fragments in different diseases may reflect different underlying mechanisms responsible for GBM damage.