Allele Substitution of the Streptokinase Gene Reduces the Nephritogenic Capacity of Group A Streptococcal Strain NZ131

Abstract

To investigate the role of allelic variants of streptokinase in the pathogenesis of acute poststreptococcal glomerulonephritis (APSGN), site-specific integration plasmids were constructed, which contained either the non-nephritis-associated streptokinase gene (skc5) from the group C streptococcal strain Streptococcus equisimilis H46A or the nephritis-associated streptokinase gene (ska1) from the group A streptococcal nephritogenic strain NZ131. The plasmids were introduced by electroporation and homologous recombination into the chromosome of an isogenic derivative of strain NZ131, in which the streptokinase gene had been deleted and which had thereby lost its nephritogenic capacity in a mouse model of APSGN. The introduction of a non-nephritis-associated allelic variant of streptokinase did not rescue the nephritogenic capacity of the strain. The mutant and the wild-type strains produced equivalent amounts of streptokinase. Complementation of the ska deletion derivative with the original ska allele reconstituted the nephritogenicity of wild-type NZ131. The findings support the hypothesis that the role of streptokinase in the pathogenesis of APSGN is related to the allelic variant of the protein.Acute poststreptococcal glomerulonephritis (APSGN) is considered to be immune mediated since C3 and immunoglobulin G (IgG) are found deposited in glomeruli of patients with the disease. The symptoms of kidney injury typically appear 7 to 21 days after infection with group A streptococci (GAS). Occasionally, APSGN also occurs following infections with streptococci of groups C and G (GCS and GGS) (1,7,27,32). Since C3 deposition precedes that of IgG in the disease process (17,25), the initial activation of complement does not appear to be due to IgG deposition or the presence of immune complexes within the glomeruli. Thus, a prevalent hypothesis is that glomerular deposition of streptococcal antigen may precede the tissue damage and lead to non-immune-mediated local activation of the complement system, with subsequent deposition of C3 (8). Several streptococcal products have been suggested to be the so-called nephritogenic factor (5,22,(33)(34)(35)(36), and some of these factors have been demonstrated in glomeruli of APSGN patients (34). Of the implicated factors, streptokinase has received especial attention. Streptokinase is considered a spreading factor for GAS, GCS, and GGS, forming a tight 1:1 stoichometric complex with either plasminogen or plasmin (2). The complex can activate plasminogen to the broad specific serine protease plasmin, which has the potential to activate the complement cascade as well as to degrade fibrin clots and extracellular matrix. The enzymatic activity of the complex cannot be inhibited by the inhibitors normally acting to inhibit plasmin in plasma (3). The streptokinase gene is highly conserved, except for two polymorphic regions, designated variable regions 1 (V1) and 2 (V2) (10). By PCR amplification and restriction enzyme analysis of the V1 region of GAS isolated from patients with differe...

Rgg Influences the Expression of Multiple Regulatory Loci To Coregulate Virulence Factor Expression in Streptococcus pyogenes

“…In contrast to hasA and hasB, no difference in the quantity of hasC transcripts was detected in the rgg mutant (Table 3). Streptokinase is an activator of human plasminogen, and certain alleles, including ska from strain NZ131, have been associated with poststreptococcal acute glomerulonephritis in a rabbit model (37). DNA microarray analysis of the rgg mutant did not detect a difference in ska transcription (data not shown).…”

Extracellular Enzymes with Immunomodulating Activities: Variations on a Theme inStreptococcus pyogenes

“…An interesting hypothesis could thus be postulated: that IgG hydrolyzed by EndoS is important in the development of ARF and APSGN, where autoimmunity and antibody complexes are implicated in the disease processes. It should be noted that one of the major factors shown to contribute to the development of APSGN are the specific streptokinases (45,81), but of potential interest is the finding that a neuraminidase activity against IgG is associated with glomerulonephritis induced by S. pyogenes (79). As previously discussed, EndoS might contribute to the observed neuraminidase activity, but further investigation is needed to evaluate the importance of EndoS in the development of diseases such as ARF and APSGN…”

Structural Diversity of Streptokinase and Activation of Human Plasminogen

“…This would explain the reported associations between SK and APSGN (12) or the observed skin tissue tropism in certain GAS isolates (5). SK from nephritis-associated strain NZ131 exhibits an increased affinity to glomeruli compared to SK from nonpathogenic group C strain H46A (14), and replacement of the SK gene of NZ131 with that of H46A significantly reduces the nephritogenicity of the strain (13). As the ␤-domain polymorphic sequence is the primary source of sequence divergence between the two SK genes, such heterogeneity may account for the differential affinities to glomerular tissue and thus explain why APSGN develops in some cases.…”