C4d as a Diagnostic Tool in Proliferative GN.

Area of Science:

• Nephrology
• Immunopathology
• Complement System

Background:

• Proliferative glomerulonephritis (GN) is categorized into immune complex-mediated and complement-mediated (C3 glomerulopathy) types.
• Immune complex-mediated GN involves glomerular deposition of immune complexes/immunoglobulins (Ig) and C3, often via classical/lectin complement pathways.
• C3 glomerulopathy features C3 deposition from alternative pathway activation with minimal immune complex/Ig deposition.

Purpose of the Study:

• To determine the significance of C4d staining in C3 glomerulopathy.
• To evaluate C4d as a potential diagnostic marker differentiating immune complex-mediated GN from C3 glomerulopathy.

Main Methods:

• Analysis of glomerular C4d staining in biopsy specimens from patients with immune-complex GN (n=18), C3 GN (n=30), and postinfectious GN (n=13).
• Comparison of C4d staining patterns with immunoglobulin and C3 deposition patterns.
• Assessment of C4d staining intensity (negative, trace/1+, bright 2-3+).

Main Results:

• Bright (2-3+) C4d staining was observed in most immune complex-mediated GN specimens, mirroring Ig and C3 staining.
• C4d staining was negative in 80% and trace/1+ in 20% of C3 glomerulopathy specimens.
• Postinfectious GN showed variable C4d staining (negative in 46%, positive in 54%), suggesting alternative pathway involvement in some cases.

Conclusions:

• C4d staining serves as a positive marker for immune complex-mediated glomerulonephritis.
• The absence or minimal detection of C4d in C3 glomerulopathy distinguishes it from immune complex-mediated GN.
• C4d assessment aids in differentiating proliferative GN subtypes based on complement pathway activation.