Antigens in urine of patients with glomerulonephritis and in normal human serum which cross-react with group A streptococci: identification and partial characterization.

Hyperimmune rabbit antisera antisera against group A streptococci precipitate protein antigens present in the urines of patients with poststreptococcal AGN and other glomerulopathies and also present in normal human serum. Over 90% of patients with AGN excrete detectable amounts of cross-reactive antigens in their urines, as do approximately 20% of patients with nonstreptococcal glomerulopathies. The streptococcal antigens are present in culture supernates, and immunodiffusion reactions in agar gel show identity or partial identity of serum, urine, and streptococcal antigens with antisera prepared against either urine proteins or against whole group A streptococci. Cross-reactive antibodies are removed from rabbit antisera by absorption with streptococcal culture supernates but not by absorption with a variety of streptococcal somatic constituents. The cross-reactive antigens have been isolated from streptococcal cultures grown in synthetic medium, thus eliminating the possibility of artefact due to tissue antigens present in Todd-Hewitt broth. The principal antigens have now been purified both from AGN urine and streptococcal supernates by molecular sieve and ion-exchange chromatography. They both have a molecular weight of approximately 360,000 daltons, as estimated on columns of agarose. The urine antigen has been applied to SDS-PAGE, and the migration of the major band was consistent with a molecular weight of 85,000 daltons. Rabbit antiserum to purified urine antigen precipitates both AGN urine and streptococcal supernates. These newly recognized human antigens, which cross-react with group A streptococcal antigens, are of particular interest because of their presence in readily available biologic fluids and their preferential excretion in almost all patients with poststreptococcal AGN.