Abstract
BackgroundThis study was devised to assess the performance of anti-ribosomal P (anti-Rib-P) antibodies in the diagnosis of systemic lupus erythematosus (SLE) and the association of these antibodies with the clinical features of SLE.MethodsWe used a fluorescence enzyme immunoassay to determine anti-Rib-P levels in an SLE group, a rheumatic disease control (RDC) group (rheumatoid arthritis (RA), ankylosing spondylitis, psoriatic arthritis and juvenile idiopathic arthritis), and a healthy control (HC) group. We also determined anti-Smith antigen (anti-Sm) and anti-double-stranded DNA (anti-dsDNA) antibody levels. Receiver operating characteristic (ROC) curves were constructed and the best cut-off points for positivity were determined. Using regression analysis, the relationship between clinical variables and autoantibody levels was analyzed.ResultsIn total, 127 patients with SLE, 256 controls with other rheumatic diseases, and 100 HCs were studied. Anti-Rib-P autoantibodies were positive in 18 (14.2%) of the patients with SLE (mean concentration of 30.6 ± 46.9 U/ml) and in 2 patients with RA (0.8% of the RDC group). In addition, 12 patients with SLE (9.4%) were positive for anti-Sm (31.1 ± 40.8 U/ml) and 63 (49.6%) were positive for anti-dsDNA autoantibodies (88.4 ± 88.5 U/ml). When we assessed the 18 patients with SLE who had tested positive for anti-Rib-P, we found that 4 of these were positive for anti-Rib-P only, whereas 12 were positive for anti-Rib-P plus anti-dsDNA, and 2 were positive for all three antibodies. There were no samples positive for anti-Rib-P plus anti-Sm. The specificity, sensitivity, positive likelihood ratio, and negative likelihood ratio of anti-Rib-P for SLE diagnosis were 99.4%, 14.2%, 23.7%, and 0.86%, respectively.Caucasian ethnicity was associated with lower anti-Rib-P antibody levels. No relation was found between anti-Rib-P levels and neuropsychiatric or other clinical features.ConclusionsAnti-Rib-P autoantibodies have high specificity for SLE, and measurement of these might improve the accuracy of SLE diagnosis. In this study, we found that Caucasian ethnicity was associated with lower anti-Rib-P antibody levels.
Highlights
This study was devised to assess the performance of anti-ribosomal P antibodies in the diagnosis of systemic lupus erythematosus (SLE) and the association of these antibodies with the clinical features of SLE
With these adjustment in cut-off values, we identified a higher number of patients with SLE who were positive for either anti-ribosomal P (Rib-P) or anti-Sm, without incurring more false-positive results in the control groups than we did with the manufacturer cut-off points
We found that the levels of anti-Rib-P autoantibodies were significantly higher in the SLE group than in the healthy control (HC) group (0.07 ± 0.21 U/ml; P = 0.016) or the rheumatic disease control (RDC) group (0.6 ± 1.8 U/ml; P = 0.017)
Summary
This study was devised to assess the performance of anti-ribosomal P (anti-Rib-P) antibodies in the diagnosis of systemic lupus erythematosus (SLE) and the association of these antibodies with the clinical features of SLE. Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by multi-organ involvement and by the production of autoantibodies directed against a variety of nuclear and cytoplasmic antigens [1,2]. Some antibodies are relevant to diagnosis, whereas others are associated with prognostic features or disease activity status [2,4]. Antibodies against double-stranded DNA (antidsDNA) and Smith antigen (anti-Sm) are considered very specific for SLE diagnosis, and both are part of the immunologic classification criteria for this disease [5]. One subset of SLE-specific autoantibodies is directed against ribosomal P (Rib-P) phosphoproteins [2]. The major immunoreactive epitope of these ribosomal antigens has been localized to the 22 amino acid carboxy-terminal domain, which is present in all three proteins, and contains two phosphorylated serine residues proteins [2,8,9,10,11,12,13,14]
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