Demonstration of human nephritogenic tubular antigen in the serum and organs by radioimmunoassay.

Nephritogenic tubular epithelial antigen (Tub-Ag), which had been found in immune complexes deposited along the glomerular capillary walls of some patients with idiopathic membranous glomerulonephritis, was solubilized from renal tubuli of humans by Pronase digestion. Soluble Tub-Ag was then purified by gel filtration and ion exchange chromatography on DEAE-Sephadex. Three DEAE fractions, designated as 0.07 M, 0.13M, and 0.23 M fractions, raised antibodies in rabbits and fluoresceinated antibodies against any of these fractions reacted exclusively with luminal layer of proximal tubular epithelia. Among three fluoresceinated antibodies, however, only the one directed to 0.07 M fraction bound with immune complexes which were deposited along the glomerular capilary walls of the patients with Tub-Ag (DEAE 0.07 M fraction) was physicochemically homogenous with a S20 value of 8.2. Utilizing 125I-labeled Tub-Ag, a sensitive and quantitave radioimmunoassay of Tub-Ag was developed. Tub-Ag was demonstrated to occur naturally in serum and urine, as well as in all the organs tested including kidney, intestine, liver, spleen, stomach, heart, and lung. Tub-Ag was detected even in the sera of anephric patients on maintenance hemodialysis (60.8 +/- 7.8 radioimmunoassay units/ml), although at slightly lower levels than in those of normal individuals (69.9 +/- 10.6 units/ml). The size of serum Tub-Ag was identical to that of molecules bearing Tub-Ag activity solubilized by Pronase from all the organs tested, indicating that circulating Tub-Ag was maintained mainly by organs other than kidneys.