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The membrane attack complex in complement-mediated glomerular epithelial cell injury: formation and stability of
Abstract:
Using a model of rat membranous nephropathy (MN), we examined the relationship between the development of glomerular epithelial cell injury and the formation and stability of the membrane attack complex (MAC) of complement. Isolated rat kidneys were perfused with buffered bovine albumin (BSA) or various plasmas (complement source). Kidneys containing nephritogenic amounts of complement-fixing sheep antibody to glomerular epithelial antigens (aFx1A) perfused with BSA (n = 5), and normal kidneys perfused with normal human plasma in BSA (50% v/v, n = 6) excreted 0.30 +/- 0.02 mg protein/min/g during 90 min perfusion (control groups). When normal plasma was added to the perfusate of aFx1A kidneys at concentrations of 12.5, 25, and 50% v/v, protein excretion rose in a time- and concentration-dependent manner. Perfusions with 25% plasma resulted in baseline proteinuria from 0 to 20 min that increased to 2.8 +/- 0.9 mg/min/g at 20 to 40 min and 8.6 +/- 2.1 at 40 to 60 min (n = 4, p less than 0.01 vs control groups). Removal of plasma at 20 min did not prevent this rise in protein excretion (3.9 +/- 2.4 and 5.8 +/- 2.6 mg/min/g at 30 to 40 and 55 to 65 min respectively, p less than 0.01, n = 4). Perfusion of aFx1A kidneys with C8-deficient (C8D) human plasma (25% v/v, n = 4) or C6D rabbit serum (25% v/v, n = 2) independently produced low levels of proteinuria comparable with BSA, but in combination, the two reagents restored enhanced protein excretion (n = 2). In aFx1A kidneys containing C5b-7, addition of C8 and C9 (C6D serum) after intervals of 20, 60, or 90 min immediately reconstituted heavy proteinuria. Thus, the magnitude of MAC-induced glomerular epithelial injury in rat MN is related to the complement dose. Altered glomerular permeability is delayed with respect to the onset of complement activation. Once sufficient C5b-9 is formed, proteinuria can develop despite cessation of new MAC assembly, implying that C5b-9 persists after formation. Moreover, the C5b-7 MAC intermediate is not eliminated rapidly in this model.
Insights
This study shows that the severity of membrane attack complex (MAC)-induced glomerular injury in rat membranous nephropathy (MN) depends on the complement dose. Proteinuria development is delayed but persists even after MAC formation stops, indicating MAC stability.
Area of Science:
- Nephrology
- Immunology
- Complement System Biology
Background:
- Membranous nephropathy (MN) involves glomerular epithelial cell injury.
- The membrane attack complex (MAC) of complement is implicated in this injury.
- Understanding MAC formation and stability is crucial for MN pathogenesis.
Purpose of the Study:
- To investigate the relationship between glomerular epithelial cell injury and MAC formation/stability in a rat MN model.
- To determine the role of complement dose in the magnitude of MAC-induced injury.
- To explore the kinetics of MAC assembly and its effect on glomerular permeability.
Main Methods:
- Isolated rat kidneys were perfused with albumin or plasma as a complement source.
- Nephritogenic sheep antibody to glomerular epithelial antigens (aFx1A) was used to induce MN.
- Proteinuria levels were measured during perfusion.
- Experiments utilized complement-deficient plasmas (C8D, C6D) to dissect MAC component roles.
Main Results:
- Proteinuria increased in a time- and concentration-dependent manner with increasing plasma concentration.
- Removal of plasma did not prevent the rise in proteinuria, indicating delayed injury onset and MAC persistence.
- Complement-deficient plasmas showed low proteinuria individually, but combined (C8D + C6D) restored proteinuria.
- Addition of C8 and C9 to kidneys with C5b-7 intermediate immediately reconstituted heavy proteinuria.
Conclusions:
- The extent of glomerular epithelial cell injury in rat MN is directly related to the dose of complement.
- Glomerular permeability changes are delayed relative to complement activation onset.
- The C5b-9 MAC complex is stable after formation, and the C5b-7 intermediate is not rapidly cleared in this model.