Urinary excretion of glomerular basement membrane-related peptides in children with renal disorders.

Urinary excretion of glomerular basement membrane (GBM)-related peptides was analysed in 72 patients with a variety of renal diseases by immunoblotting using polyclonal antibodies against either collagenase or pepsin digests of human GBM. The specificity of the antibodies was verified by elution of antibodies bound to urinary GBM-related peptides on nitrocellulose blots and demonstration of reactivity of the eluted antibodies with the respective GBM digests. Furthermore, six mice immunized with urinary GBM-related peptides all developed focal linear deposits of mouse IgG along their GBM, linear and mesangial deposits of C3 in the glomeruli and serum antibodies reactive with human GBM. Monoclonal antibodies against urinary GBM-related peptides of one of the mice reacted with different peptides of the non-collagenous and collagenous domains of type IV collagen, the major structural protein of GBM. In the majority of the 75 patients' urines tested, excretion of GBM-related peptides with molecular weights of 33, 50, 80 and 150 kilodaltons (kD) was detectable. Patients with a diminished glomerular filtration rate (GFR) demonstrated excretion of the 33 kD peptide more frequently (91%) and never of the 80 kD peptide as compared with patients with normal GFR (33 kD [42%] 80 kD [87%]). The pattern of urinary GBM-related peptides was not specific for the underlying renal disease as in Alport's syndrome.