Presence of circulating antibodies against brush border antigens (Fx1A) in a patient with membranous nephropathy and bilateral pyeloureteral stenosis. Comparison with idiopathic membranous nephropathy.

In a patient with membranous nephropathy and bilateral pyeloureteral stenosis with hydronephrosis, we examined the possibility that an increase in the intratubular pressure could facilitate the passage of the Fx1A antigens to the circulation. Elevated serum anti-Fx1A antibodies were detected in this particular patient by ELISA on three occasions during the disease follow-up, even though he was in clinical remission. These antibodies reacted in vitro with the tubular brush border of a normal human kidney. The anti-Fx1A antibodies isolated from the patient's sera by affinity chromatography competed with the rabbit anti-Fx1A antisera binding to plates coated with human Fx1A antigen. In immunoblotting studies the isolated specific IgG antibodies from that patient reacted with a 180 kDa antigen of the human Fx1A and with less intensity with 75 kDa and 50-55 kDa polypeptides. In none of 12 patients with idiopathic membranous nephropathy could the circulating anti-Fx1A antibodies be demonstrated. On the whole, this particular case suggests that on some occasions increased intratubular pressure could cause the release of Fx1A antigens, facilitating an autologous immunocomplex nephritis. These antigens, by contrast, do not seem to play any role in most cases of membranous nephropathy in man.