Background and objectives Systemic lupus erythematosus (SLE) is characterised by the production of autoantibodies directed against a variety of nuclear and cytoplasmic antigens. One of these antigens is ribosomal P protein (Rib-P), a pentamer consisting of three different phosphoproteins. The aim of this work was to assess the prevalence and clinical associations of anti-Rib-P antibodies in a cohort of Portuguese SLE patients.
Patients and methods Anti-Rib-P autoantibodies were quantified in sera from 127 SLE patients, 100 healthy controls and 256 various control diseases including rheumatoid arthritis (n=100), JIA (n=34), AS (n=100) and PsA (n=22) using the EliA Rib-P (Phadia, Sweden), a fluoroenzymeimmunoassay that quantifies Rib-P specific IgG antibodies.
Results The mean value of anti-Rib-P was significantly higher in SLE patients than in healthy (p<0.001) or disease control population (p=0.002). Setting the cut-off for positivity at 4.45 U/ml as determined by Receiver Operating Characteristic (ROC) curve analysis, 18 SLE patients (14.2%) but no healthy controls were positive for anti-Rib-P autoantibodies (Rib-P-(+)) (p<0.001); in the disease control group only two rheumatoid arthritis patients were Rib-P-(+) (p<0.001).
The area under the curve was 0.800 for discrimination between SLE and healthy controls (sensitivity=14.2%; specificity=100%) and 0.595 for control diseases (sensitivity=14.2%; specificity=99.2%).
SLE patients Rib-P-(+) had a higher SLEDAI (p=0.005), but no association with psychosis or nephritis was found. Also there was no relation with age, age at diagnosis, gender or ethnicity. The authors also compared anti-Rib-P autoantibodies with the production of other autoantibodies (such as anti-dsDNA, anti-Sm or APL) and found no statistically significant associations.
Conclusion Considering the high specificity of this test, the authors believe that anti-Rib-P autoantibody quantification through this method might be useful in SLE diagnosis. Its value as an indicator of active disease needs to be prospectively validated.
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