Antiribosomal P protein IgG autoantibodies are highly specific for SLE and might be associated with disease activity

Abstract

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 antidsDNA, 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.