Complement C3c Reflects Acute-Phase Response but Not Clinical Phenotype in Systemic Sclerosis: A Cross-Sectional...

Area of Science:

• Rheumatology
• Immunology
• Clinical Chemistry

Background:

• Systemic sclerosis (SSc) is a complex autoimmune disease.
• Complement system proteins, including C3c and C4, play roles in inflammation.
• The utility of routine complement measurements in SSc management is not fully understood.

Purpose of the Study:

• To evaluate the association of serum complement C3c and C4 levels with systemic inflammation markers.
• To investigate the relationship between C3c/C4 and clinical/immunological phenotypes in SSc.
• To assess the correlation of C3c/C4 with patient-reported outcomes (PROs) in SSc.

Main Methods:

• Seventy SSc patients were assessed for serum C3c, C4, CRP, ESR, IL-6, autoantibodies, and PROs.
• Spearman correlations and linear regression analyses were employed.
• Comparisons were made between SSc patients with and without secondary Sjögren's disease (SjD).

Main Results:

• Serum C3c strongly correlated with CRP and ESR, independently predicting ~15-17% of their variance.
• Serum C4 showed weaker correlations with CRP and ESR.
• Neither C3c nor C4 correlated with IL-6, skin score, lung disease, GI involvement, autoantibodies, therapy, or PROs.
• C3c and C4 levels were lower in SSc patients with secondary Sjögren's disease.

Conclusions:

• Serum C3c serves as a marker of the acute-phase response in SSc, mirroring CRP and ESR.
• Complement C3c and C4 levels do not reflect the clinical phenotype or patient-perceived burden in SSc.
• Routine C3c and C4 measurements may offer limited value beyond assessing acute inflammation in SSc.