Ricinus communis agglutinin I blocks the binding of human anti-renal basement membrane antibodies to the kidney.

Whether or not glycosyl moieties of glycoproteins present in human renal basement membranes are related to the sites where anti-basement membrane antibodies bind was examined by blocking experiments using several kinds of lectin. Ricinus communis agglutinin I (RCA I), specific for galactose, blocked the binding of human anti-glomerular basement membrane (GBM) and anti-tubular basement membrane (TBM) antibodies to renal basement membranes. This lectin also diminished the binding of rabbit anti-laminin antibody, but did not inhibit the binding of mouse anti-fibronectin or rabbit anti-human TBM antibodies. These findings suggest that the binding sites of human anti-GBM and anti-TBM antibodies and heteroantibodies to laminin are closely related to the galactose moieties in glycoproteins of human renal basement membranes. Whether the galactose-containing branches are associated with the nephritogenicity of human anti-GBM and anti-TBM antibodies or simply exist adjacently to the antibody binding sites remains to be discerned.