Background: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by tissue injury mediated by inflammatory mechanisms. Nonetheless, several acute-phase proteins may remain normal or are decreased. We explore the association of diverse biomarkers with selected clinical features, disease activity, and organ damage in SLE.
Methods: One hundred and fifteen SLE patients were analyzed for clinical manifestations, disease activity, and organ damage. Serum C-reactive protein (CRP), complement C3, C4 and CH50%, alpha-1-antitrypsin (AAT), transferrin (Tf), procalcitonin, erythrosedimentation rate (ESR), and interleukin-6 were measured in patients and twenty-six healthy blood donors. Statistics include chi-square, Kruskal-Wallis (post hoc by Mann-Whitney) or one-way ANOVA tests (post hoc by t tests) as appropriate. Associations were evaluated by the Spearman's correlation coefficient (p).
Results: SLE patients have lower C3 (85 vs. 110 mg/dL; p < 0.0001) and C4 (14.2 vs. 24.2 mg/dL; p < 0.0001) than controls, while CRP (4.1 vs. 1.4 mg/L; p = 0.005) and AAT (147 vs. 138 mg/dL; p = 0.03) were higher, other biomarkers were irrelevant. Disease activity score positively correlated with ESR (p = 0.23, 95 % CI 0.04 to 0.4; p = 0.01) and CRP (p = 0.19, 0.0007 to 0.36; p = 0.04), while inverse correlations with C3 (p = -0.26, -0.43 to -0.08; p = 0.004), C4 (p = -0.18, -0.36 to 0.005; p = 0.04), CH50 % (p = -0.20, -0.38 to -0.01; p = 0.02), and Tf (p = -0.35, -0.53 to -0.12; p = 0.002) were found. According to clinical manifestations, patients with arthritis showed higher levels of ESR (34 vs. 20 mm/h), CRP (10 vs. 2.8 mg/L), and AAT (179 vs. 145 mg/dL), but lower Tf (192 vs. 226 mg/dL) than those without arthritis; whereas active nephritis was characterized by lower serum concentrations of complement C3 (73 vs. 92 mg/dL), C4 (10 vs. 15 mg/dL), CH50% (80 vs. 160 U/mL) and Tf (196 vs. 232 mg/dL) than those patients without this manifestation. No other significant differences were found.
Conclusions: In patients with SLE, acute-phase proteins behave differently depending on the kind of organ damage evaluated. Serum complement proteins remained as the most reliable laboratory markers for nephritis, while CRP was determined the best in patients with arthritis. The muted CRP response seen in SLE patients with active nephritis could have important pathogenic implications.