C3 and interstitial lung disease: Logistics regression analysis was applied to study the relationships of the differentially expressed serum biomarkers, including anti-CCP antibody, IgG, C3, C4, IL-1ß, IL-5, IL-6, IL-17, IL-12p70, TNF-α, and INFγ), between pSS-N-ILD and pSS-ILD.