Diagnostic value and clinical laboratory associations of antibodies against recombinant ribosomal P0, P1 and P2 proteins and their native heterocomplex in a Caucasian cohort with systemic lupus erythematosus

INTRODUCTION: In this study, we sought to determine the diagnostic value and clinical laboratory associations of autoantibodies against recombinant ribosomal P0, P1 and P2 proteins and their native heterocomplex in systemic lupus erythematosus (SLE). METHODS: Autoantibodies against recombinant ribosomal P proteins (aRibP(R)0, aRibP(R)1 and aRibP(R)2) and antibodies against native ribosomal P heterocomplex (aRibP(N)H) were determined in sera from patients with SLE (n = 163), systemic sclerosis (n = 66), Sjögren's syndrome (n = 54), rheumatoid arthritis (n = 90) and healthy donors (n = 100) using enzyme-linked immunosorbent assay. Test results were correlated to medical records, including the American College of Rheumatology criteria, the Systemic Lupus Erythematosus Disease Activity Index 2000, laboratory data and medications of all SLE patients. RESULTS: Sensitivities of 22.0% for aRibP(R)0, 14.9% for aRibP(R)2, 14.3% for aRibP(N)H and 10.7% for aRibP(R)1 were obtained at a specificity of 99%. The assay for aRibP(R)0 detection demonstrated the best performance in receiver-operating characteristics analysis, with aRibP(R)0 detectable in 10% of anti-Smith antibody and anti-double-stranded DNA-negative sera at a specificity of 100%. ARibP(R)0 positivity was associated with lymphocytopenia. ARibP(R)1(+ )patients had significantly higher γ-glutamyl transpeptidase (GGT) levels than their aRibP(R)1(- )counterparts. No specific damage occurred in aRibP(+ )lupus patients compared with a group of age-, sex- and nephritis-matched aRibP(- )lupus patients within 3 years. CONCLUSIONS: The determination of antibodies against ribosomal P proteins improves the diagnosis of SLE and should therefore be implemented in upcoming criteria for the diagnosis or classification of SLE. High titers of aRibP(R)0 can be associated with lymphocytopenia, and high titers of aRibP(R)1 can be associated with elevated GGT levels. So far, there is no evidence for a prognostic value of aRibPs for damage.