Insights on the relationship between complement component C4 serum concentrations and C4 gene copy numbers in a Western Australian systemic lupus erythematosus cohort

Usefulness and analytical performances of complement multiplex assay for measuring complement biomarkers in plasma

INTRODUCTION

The complement system is involved in numerous diseases, through diverse mechanisms and degree of activation. With the emergence of complement targeting therapeutic, simple and accessible tools to evaluate the extent of complement activation are strongly needed.

METHODS

We evaluated two multiplex panels, measuring complement activation fragments (C4a, C3a, C5a, Bb, Ba, sC5b9) and intact components or regulators (C1q, C2, C3, C4, C5, FD, FP, FH, FI). The specificity of each measurement was assessed by using complement proteins depleted sera and plasma collected from patients with complement deficiencies. Normal values distribution was estimated using 124 plasma samples from healthy donors and complement activation profile was assessed in plasma collected from 31 patients with various complement-mediated disorders.

RESULTS

We observed good inter-assay variation. All tested protein deficiencies were accurately detected. We established assay-specific reference values for each analyte. Except for C3, C4 and C4a, the majority of the measurements were in good agreement with references methods or published data.

CONCLUSION

Our study substantiates the utility of the Complement Multiplex assay as a tool for measuring complement activation and deficiencies. Quantifying complement cleavage fragments in patients exhibiting classical or alternative pathway activation allowed evaluating the activation state of the whole cascade.

Complement as a Biomarker for Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a disease of immune complex deposition; therefore, complement plays a vital role in the pathogenesis of SLE. In general, complement levels in blood and complement deposition in histological tests are used for the management of SLE. Thus, the evaluation of complement status can be useful in the diagnosis of SLE, assessment of disease activity, and prediction of treatment response and prognosis. In addition, novel complement biomarkers, such as split products and cell-bound complement activation products, are considered to be more sensitive than traditional complement markers, such as serum C3 and C4 levels and total complement activity (CH50), which become more widely used. In this review, we report the complement testing in the management of SLE over the last decade and summarize their utility.

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

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/µL), 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.