A new role for complement in experimental membranous nephropathy in rats

Area of Science:

• Nephrology
• Immunology
• Complement System Biology

Background:

• The complement system's role in renal disease was primarily linked to neutrophil-mediated glomerular injury.
• Passive Heymann nephritis (PHN) is a model of experimental membranous nephropathy characterized by subepithelial immune deposits and proteinuria.
• The specific mechanisms by which complement contributes to proteinuria in PHN remained unclear.

Purpose of the Study:

• To investigate the role of complement, specifically complement component 3 (C3), in mediating proteinuria in the PHN model.
• To determine if proteinuria in PHN is dependent on neutrophil infiltration.

Main Methods:

• Rats with PHN were depleted of C3 using cobra venom factor and compared to untreated controls.
• Subepithelial immunoglobulin deposition was assessed in C3-depleted and control rats.
• The effect of C3 fixation by different antibody subclasses (gamma1 vs. gamma2) on proteinuria was examined.
• Neutrophil counts were assessed, and rats were depleted of neutrophils to evaluate their role in PHN-induced proteinuria.

Main Results:

• C3 depletion completely abolished proteinuria in PHN rats, despite similar immunoglobulin deposition.
• Non-complement-fixing antibody portions (F(ab')2) and the gamma2 subclass induced immunoglobulin deposition without C3 and without proteinuria.
• The gamma1 subclass induced C3 fixation and heavy proteinuria.
• Neutrophil depletion did not reduce proteinuria in PHN rats, indicating a neutrophil-independent mechanism.

Conclusions:

• Proteinuria in the PHN model of membranous nephropathy is critically dependent on complement activation.
• The findings strongly suggest a neutrophil-independent mechanism for complement-mediated glomerular injury in this model.
• This study identifies a novel role for the complement system in mediating immunologic glomerular injury.