A role of streptokinase in experimental post-streptococcal glomerulonephritis

Abstract

Post-streptococcal glomerulonephritis (PSGN) refers to the sequela of the acute infection, caused by Streptococcus pyogenes (group A streptococcus, GAS). This pathology has been studied for a long time, and today attempts are being made to identify the products of their life activity, able to initiate an immunopathological process in kidneys. Most attention has been paid to streptokinase, the enzyme transforming blood plasminogen into plasmin, capable, together with the plasmin receptor (NAPlr), of damaging the glomerular tissue, as well as activating the complement system. The aim of the study was to consider two tasks: to study the ability of the GAS-obtained enzyme to transform plasminogen of different species into plasmin as well as to study its role in the development of PSGN in rabbits having subcutaneously implanted tissue chambers. The animals were infected by inoculating GAS cultures into the chambers. Materials and methods. GAS strains of M types 1, 12, 22 and their ska– isogenic mutants were used in the study. Purified plasminogen preparations were isolated from fresh human, rabbit or mouse plasma by using chromatographic column with Lysine Sepharose 4B. To reveal the ability of streptokinase to activate plasminogen into plasmin, its preparation at a concentration of 1 mg/ml was added to 10 ìg of purified human, rabbit or mouse plasminogen. The concentration of plasmin was defined photometrically using S-2251 (Chromogenix, USA). To reproduce PSGN, four chambers were implanted under the skin in each rabbit; after the complete wound healing animals were infected and observed for three weeks. On day 14, the animals were treated with benzylpenicillin. The kidneys from survived rabbits were subjected to immunohistology analysis. Results. During in vitro experiments, M1, M12 and M22 GAS streptokinase showed distinct functional activity on human plasminogen, transforming it into plasmin: optical density indicators at ë = 405 nm were 0.4–0.7 compared with the negative control (ОD < 0.001). Streptokinase did not activate mouse plasminogen (ОD = 0.001) and exerted quite a weak effect on transformation of the rabbit plasminogen into plasmin (ОD = 0.002). In experiments on PSGN induction in rabbits, we failed to detect streptokinase involvement, because no differences between initiation of glomerulonephritis by wild strains or ska– isogenic mutants were identified. Mutant strains deficient in the gene responsible for streptokinase synthesis but retained ability to bind rabbit and human IgG, caused morphological changes in kidney tissue, specific for PSGN. In addition, a comparative analysis of PSGN “rabbit” and “mouse” models developed by the same technology, was carried out and led to opposing conclusions regarding a role of streptokinase in pathogenesis of experimental glomerulonephritis. The role of IgG Fc-binding activity of GAS in development of experimental PSGN is discussed.