The immunolocalization and urinary quantitation of 7-5Q/A, a unique human renal antigen

In this communication 7-5Q/A, a recently described human kidney-specific acidic membrane glycoprotein, was immunolocalized by immunofluorescence in kidney and placenta, and by immunogold electron microscopy in the kidney. The antigen is located above and below the slit diaphragm on epithelial cell foot processes in the glomerulus, and also on proximal tubular brush border membranes. In the placenta it was present on epithelial membranes. 7-5Q/A and dipeptidylpeptidase IV were compared by a variety of techniques because of their similar size and possible location, and found to be distinct. A sensitive sandwich ELISA was developed using polyclonal and monoclonal antibodies to 7-5Q/A, and applied to the quantitation of this antigen in the urines and sera of patients with a variety of kidney diseases, and in the urines and sera of normal subjects. The concentration of 7-5Q/A in normal urines ranged from 0 to 2 ng/ml but levels of up to 150 ng/ml were found in urines of patients with renal disease. 7-5Q/A was not detectable in either normal or nephritic sera. Urinary quantitation of this unique antigen may be of value in the early diagnosis of renal disease.