Elevated Serum Levels of Interferon-Regulated Chemokines Are Biomarkers for Active Human Systemic Lupus Erythematosus

BACKGROUND: Systemic lupus erythematosus (SLE) is a serious systemic autoimmune disorder that affects multiple organ systems and is characterized by unpredictable flares of disease. Recent evidence indicates a role for type I interferon (IFN) in SLE pathogenesis; however, the downstream effects of IFN pathway activation are not well understood. Here we test the hypothesis that type I IFN-regulated proteins are present in the serum of SLE patients and correlate with disease activity. METHODS AND FINDINGS: We performed a comprehensive survey of the serologic proteome in human SLE and identified dysregulated levels of 30 cytokines, chemokines, growth factors, and soluble receptors. Particularly striking was the highly coordinated up-regulation of 12 inflammatory and/or homeostatic chemokines, molecules that direct the movement of leukocytes in the body. Most of the identified chemokines were inducible by type I IFN, and their levels correlated strongly with clinical and laboratory measures of disease activity. CONCLUSIONS: These data suggest that severely disrupted chemokine gradients may contribute to the systemic autoimmunity observed in human SLE. Furthermore, the levels of serum chemokines may serve as convenient biomarkers for disease activity in lupus

Circulating immune complexes contain citrullinated fibrinogen in rheumatoid arthritis

INTRODUCTION: There is increasing evidence that autoantibodies and immune complexes (ICs) contribute to synovitis in rheumatoid arthritis (RA), yet the autoantigens incorporated in ICs in RA remain incompletely characterised. METHODS: We used the C1q protein to capture ICs from plasma derived from human RA and control patients. Antibodies specific for immunoglobulin were used to detect ICs, and fibrinogen antibodies were used to detect fibrinogen-containing ICs. RA and control plasma were separated by liquid chromatography, and fractions then characterised by ELISA, immunoblotting and mass spectrometry. Immunohistochemical staining was performed on rheumatoid synovial tissue. RESULTS: C1q-immunoassays demonstrated increased levels of IgG (p = 0.01) and IgM (p = 0.0002) ICs in plasma derived from RA patients possessing anti-cyclic citrullinated peptide (CCP+) autoantibodies as compared with healthy controls. About one-half of the anti-CCP+ RA possessed circulating ICs containing fibrinogen (p = 0.0004). Fractionation of whole RA plasma revealed citrullinated fibrinogen in the high molecular weight fractions that contained ICs. Positive correlations were observed between fibrinogen-containing ICs and anti-citrullinated fibrinogen autoantibodies, anti-CCP antibody, rheumatoid factor and certain clinical characteristics. Immunohistochemical staining demonstrated co-localisation of fibrinogen, immunoglobulin and complement component C3 in RA pannus tissue. Mass spectrometry analysis of immune complexes immunoprecipitated from RA pannus tissue lysates demonstrated the presence of citrullinated fibrinogen. CONCLUSION: Circulating ICs containing citrullinated fibrinogen are present in one-half of anti-CCP+ RA patients, and these ICs co-localise with C3 in the rheumatoid synovium suggesting that they contribute to synovitis in a subset of RA patients

Coordinate Dysregulation of Serum Protein Levels in SLE

<p>Hierarchical clustering was applied to protein levels of the identified analytes (“Serum Protein Levels”). Individual data points represent the log₂ ratio of the analyte concentration to the mean of control concentrations (scale shows linear fold-differences). “In Vitro Control PBMC Gene Expression” columns present gene expression microarray data obtained by incubating normal control PBMCs in vitro with medium alone or with type I IFN for 6 and 24 h. Data are normalized to control medium-alone conditions (scale depicts linear fold-differences). Grey boxes indicate missing data. Analytes induced by type I IFN in vitro (>2-fold and >500 expression unit mean difference) are highlighted in red font.</p

IFN-Regulated Chemokines Are Associated with SLE Disease Activity

<p>Shown are 20 serum analytes that exhibited significant positive (highlighted in yellow) or negative (highlighted in blue) correlation coefficients with clinical measures of SLE. The IFN gene score was calculated from 82 IFN-inducible transcripts measured by concurrent whole blood gene expression microarrays. The chemokine protein “score” was calculated using the seven IFN-regulated CC and CXC chemokines highlighted in red. * <i>p</i> < 0.05; ** <i>p</i> < 0.01; *** <i>p</i> < 0.001; **** <i>p</i> < 0.0001. <i>p</i>-Values were obtained by permutation testing.</p