IgG subclasses and complement pathway in segmental and global membranous nephropathy

Area of Science:

• Nephrology
• Immunology
• Pathology

Background:

• Idiopathic membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults.
• The role of immunoglobulin G (IgG) subclasses and complement activation in MN pathogenesis remains incompletely understood.
• Understanding these interactions is crucial for developing targeted therapies.

Purpose of the Study:

• To elucidate the association between specific immunoglobulin G (IgG) subclasses and complement pathway activation in patients with idiopathic membranous nephropathy (MN).
• To differentiate complement profiles between segmental MN (S-MN) and global MN (G-MN).

Main Methods:

• Immunofluorescence (IF) analysis was performed on kidney biopsies from 16 MN patients and 20 controls.
• Antibodies targeting IgG subclasses (IgG1-4), complement components (C1q, C3c, C4d, MBL, factor B, C5b-9), and CD59 were utilized.
• MN was classified as segmental (S-MN) or global (G-MN) based on IgG deposit distribution.

Main Results:

• Segmental MN (S-MN) showed deposits of IgG1, IgG3, C1q, C3c, C4d, C4-binding protein (C4-bp), C5b-9, and CD59, indicating classical complement pathway activation.
• Global MN (G-MN) exhibited deposits of IgG1, IgG2, IgG3, IgG4, C3c, C4d, mannose-binding lectin (MBL), factor B, C4-bp, C5b-9, and CD59, suggesting activation of both alternative and lectin pathways.
• G-MN had higher IgG1, IgG2, and IgG4 deposition compared to S-MN.
• S-MN demonstrated higher C1q intensity, while G-MN showed increased factor B and MBL intensity.

Conclusions:

• This study is the first to report distinct complement activation patterns in S-MN and G-MN.
• S-MN is associated with classical complement pathway activation mediated by IgG1 and IgG3.
• G-MN is linked to alternative and lectin pathway activation involving IgG2 and IgG4.