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Post-streptococcal glomerulonephritis: studies on the interaction between nephritis strain-associated protein (NSAP),
P W Peake1, B A Pussell, T E Karplus
1Department of Nephrology, Prince Henry Hospital, Little Bay, NSW, Australia.
Summary
Nephritis strain-associated protein (NSAP) from Streptococcus activates complement and binds to human glomeruli, suggesting a role in acute glomerulonephritis. This streptococcal antigen may initiate glomerular injury by binding before complement and antibody fixation.
Area of Science:
- Immunology
- Nephrology
- Microbiology
Background:
- Nephritis strain-associated protein (NSAP) is a streptokinase implicated in acute glomerulonephritis.
- NSAP is a potential specific antigen contributing to glomerular injury.
Purpose of the Study:
- To investigate the mechanisms of NSAP-induced glomerular damage.
- To examine NSAP's ability to activate complement in vitro.
- To assess NSAP's binding affinity to isolated human glomeruli.
Main Methods:
- Complement activation assays using normal human serum.
- Measurement of complement breakdown products (C3a, C4a).
- Scatchard analysis for NSAP binding to human glomeruli.
Main Results:
- NSAP, alone and with antibody, depleted complement, generating C3a and C4a.
- NSAP exhibited strong binding to human glomeruli (Ka = 400 x 10^6 M).
- NSAP binding was significantly higher than non-nephritic streptokinase or cationized albumin.
Conclusions:
- Findings support the hypothesis that NSAP binding to glomeruli precedes complement and antibody fixation.
- NSAP may play a direct role in initiating glomerular injury in acute glomerulonephritis.
- Streptococcal antigen deposition is a potential key step in the pathogenesis of this kidney disease.