Establishing a Case for Anti-complement Therapy in Membranous Nephropathy.

Area of Science:

• Nephrology
• Immunology
• Pathophysiology

Background:

• Membranous nephropathy (MN) is a leading cause of adult nephrotic syndrome, often progressing to kidney failure.
• It is an autoimmune glomerular disease characterized by IgG deposits, where complement activation is known to cause kidney damage in experimental models.
• The specific role of complement in human MN remains less defined.

Purpose of the Study:

• To investigate the role of complement activation in the pathogenesis of primary membranous nephropathy (pMN).
• To analyze complement protein levels in kidney biopsies and urine from pMN patients.

Main Methods:

• Laser capture microdissection and mass spectrometry of glomeruli from pMN patients (n=11) and controls (n=5) to identify complement proteins.
• Immunohistological staining for complement proteins in pMN biopsy specimens.
• Measurement of urine complement activation products (Ba, C5a, C5b-9 [MAC]) in a separate pMN cohort (n=13).

Main Results:

• Mass spectrometry identified elevated levels of complement pathway components (C1q, C3, C4, C5, C6, C7, C8, C9) and decreased levels of complement receptor 1 (CR1) in pMN glomeruli compared to controls.
• Immunohistology confirmed positive staining for C3, C4, and lectin pathway components, with absent/trace C1q in pMN biopsies.
• Urine analysis revealed the presence of Ba, C5a, and MAC in pMN patients, with strong correlations between these markers.

Conclusions:

• Elevated glomerular C3, C4, and MAC, alongside reduced CR1, support complement system involvement in MN pathogenesis.
• Increased urinary complement activation products further indicate complement's role in disease.
• These findings suggest that anti-complement therapies could be a potential treatment strategy for certain forms of MN.