Demonstration of streptococcal antigens produced in vivo and identification of a nephritis associated protein.

An experimental infectious model in rabbits was used to study the release of bacterial substances in vivo in relation to the development of renal lesions, using three different group A Streptococci (type M56, M12 and T3). Three weeks post infection, renal lesions were confirmed in animals infected with M56 and M12, but not T3 streptococci, by histological and immunohistological analyses of the kidneys. Tissue-cage fluid (TCF) from the potentially nephritogenic strains (M56 and M12) showed a time-related increase of proteins and a production of streptococcal antibodies in serum. Isoelectrofocusing of TCF from nephritogenic and non-nephritogenic strains showed the presence of "nephritogenic-strain-specific" proteins in the most cationic region as well as in pH region 5.8-6.4. Immunoblotting after SDS-PAGE of TCF revealed a nephritogenic-strain-restricted protein that, by means of a mouse-monoclonal antibody, identified with the NSAP (Nephritic-Strain-Associated Protein). The biological activity demonstrated in the focus of infection using the M56 and M12 strains thus seems to be related in time to the induction of the nephritic process.