Urinary C4 excretion in systemic lupus erythematosus

Area of Science:

• Nephrology
• Immunology
• Rheumatology

Background:

• Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by systemic inflammation.
• Monitoring SLE disease activity and predicting flares are crucial for patient management.
• The role of complement component 4 (C4) in SLE pathogenesis and as a biomarker is under investigation.

Purpose of the Study:

• To assess the utility of urinary C4 as a biomarker for SLE disease activity.
• To investigate the relationship between urinary C4 levels and SLE flare-ups.
• To explore the nature and origin of urinary C4 in SLE patients.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA) was used to measure urinary C4 in 19 SLE patients.
• Serial measurements of urinary C4 were performed in 13 patients.
• Specific hemolytic activity and Western blotting were employed to analyze urinary C4 composition.
• The effect of camostat, a serine protease inhibitor, on urinary C4 excretion was examined in two cases.

Main Results:

• Urinary C4 was detectable in all SLE patients studied.
• A decrease in urinary C4 levels correlated with decreased SLE disease activity in 11 of 13 patients.
• Increased urinary C4 preceded disease flares in two patients.
• Urinary C4 primarily consisted of degraded C4 fragments.
• Camostat administration reduced urinary C4 excretion, suggesting intra-glomerular complement activation.

Conclusions:

• Urinary C4 measurement is a potentially valuable tool for monitoring SLE disease activity.
• Urinary C4 levels may aid in predicting SLE flare-ups.
• The findings suggest complement activation within the glomerulus in lupus nephritis.