Association between IgG4 Autoantibody and Complement Abnormalities in Systemic Lupus Erythematosus

Area of Science:

• Immunology
• Rheumatology
• Nephrology

Background:

• Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by diverse autoantibodies and complement abnormalities.
• The role of immunoglobulin G4 (IgG4) autoantibodies in SLE pathogenesis and their association with complement system function remain incompletely understood.

Purpose of the Study:

• To investigate the association between IgG4 autoantibodies and complement abnormalities in patients with SLE.
• To explore the correlation between serum IgG4 levels and clinical parameters in SLE.
• To analyze IgG subclass deposition in lupus nephritis (LN) and its relationship with complement components.

Main Methods:

• Serum levels of antinuclear IgG4 and IgG4-specific IgM-rheumatoid factor (RF) were measured in 72 SLE patients, 67 rheumatoid arthritis (RA) patients, and 41 healthy controls.
• Correlations between serum antinuclear IgG4 levels and clinical parameters, including 24-hour urinary protein, were analyzed.
• Levels of IgG subclasses, C1q, and C3 deposition were detected in kidney biopsies from patients with lupus nephritis (LN).

Main Results:

• Serum antinuclear IgG4 levels were significantly higher in SLE patients compared to healthy controls (P < 0.01).
• In SLE patients, antinuclear IgG4 levels positively correlated with total IgG4, albumin, and C3, and negatively with 24-hour urinary protein.
• In LN, the ratio of IgG4 deposition to total IgG deposition negatively correlated with C1q and C3 deposition scores.

Conclusions:

• Elevated IgG4 autoantibodies in SLE may be associated with a dampened inflammatory response.
• The findings suggest that IgG4 autoantibodies might play a protective role in SLE.
• IgG4 autoantibodies represent a potential novel therapeutic target for managing SLE and its complications.