Plasma Free Protein S Is Correlated with Disease Activity, but not with Subclinical Atherosclerosis among Patients with Systemic Lupus Erythematosus: A Cross-Sectional Study

Abstract

A defect in clearance of apoptotic materials is pivotal in the pathogenesis of systemic lupus erythematosus (SLE). Protein S participates in the removal of apoptotic remnants and the anticoagulation pathway. The aim of the study was to clarify the relationship between plasma levels of free protein S and the disease activity or subclinical atherosclerosis in SLE. Free protein S was measured by an enzyme-linked immunosorbent assay, and patients were classified into two groups of free protein S levels: low (< 50%) and normal (>/= 50%). One hundred-eleven Korean female patients with SLE were enrolled, and the levels of free protein S were 67.4 +/- 19.7%. Carotid plaque was detected in 25 (22.5%) patients. Twenty-one patients with low free protein S had lower hemoglobin (11.4 +/- 1.4 vs. 12.5 +/- 1.4 g/dL) and lymphocytes (1,221 +/- 609 vs. 1,720 +/- 1,097/microL), higher erythrocyte sedimentation rate (30.1 +/- 20.6 vs. 20.8 +/- 17.8 mm/h), and lower complement 3 (80.8 +/- 27.6 vs. 103.4 +/- 25.8 mg/dL) and complement 4 (15.6 +/- 10.4 vs. 21.5 +/- 7.6 mg/dL) than those with normal protein S. There was no significant difference in the proportion of patients with increased carotid artery intima-media thickness (> 4.6 mm) or with carotid artery plaque between two groups. The low levels of free protein S were associated with hemoglobin (OR = 0.64, p = 0.04) and complement 3 (OR = 0.96, p = 0.005). Free protein S is correlated with disease activity, but not with subclinical atherosclerosis in SLE.