Circulating immune complexes in lupus erythematosus, scleroderma and dermatomyositis

Area of Science:

• Rheumatology
• Immunology
• Clinical Chemistry

Background:

• Circulating immune complexes (CIC) are implicated in the pathogenesis of autoimmune diseases.
• Their presence and significance vary across different connective tissue diseases.
• Understanding CIC levels aids in diagnosing and monitoring autoimmune conditions like SLE.

Purpose of the Study:

• To measure CIC levels in patients with systemic lupus erythematosus (SLE) and related conditions.
• To investigate the correlation between CIC and complement levels (C4, C3) in SLE.
• To assess CIC presence in drug-induced lupus, discoid lupus, systemic sclerosis, and dermatomyositis.

Main Methods:

• Serum samples were collected from patients diagnosed with SLE, hydralazine-induced SLE-like syndrome, discoid lupus (DLE), systemic sclerosis, and dermatomyositis.
• Circulating immune complexes (CIC) were quantified using three distinct assay methods.
• Serum complement levels (C4 and C3) were measured and correlated with CIC concentrations.

Main Results:

• CIC were detected in 13 out of 17 SLE patients, notably in all with lupus nephritis and typical exanthema.
• A significant inverse correlation was observed between CIC concentration and serum C4/C3 levels in SLE.
• All three patients with hydralazine-induced SLE-like syndromes had detectable CIC, which resolved upon drug withdrawal. CIC were found in 3/14 DLE patients, 1/8 systemic sclerosis patients, and 4/5 dermatomyositis patients.

Conclusions:

• Circulating immune complexes are a common biomarker in systemic lupus erythematosus, particularly in severe manifestations.
• Drug-induced lupus associated with hydralazine shows transient CIC, highlighting the drug's role.
• CIC detection may be relevant in discoid lupus and dermatomyositis, though complement consumption was not observed in dermatomyositis.