Evaluation of anti-ribosomal P protein immunoassay in Japanese patients with connective tissue diseases: comparison with an indirect immunofluorescence assay.
OBJECTIVE
To investigate the prevalence of anti-ribosomal P protein (anti-P) antibodies in Japanese patients with connective tissue diseases (CTDs) using enzyme-linked immunosorbent assays (ELISAs) and western blotting (WB) and to evaluate the indirect immunofluorescence (IIF) staining patterns of anti-P-positive sera.


METHODS
Anti-P antibodies were measured by two different commercially available ELISA kits and WB in 239 outpatients, 99 with systemic sclerosis (SSc), 73 with systemic lupus erythematosus (SLE), 45 with dermatomyositis (DM), and 22 with Sjögren's syndrome (SjS). Sera positive for anti-P antibodies by WB were analysed by IIF.


RESULTS
The frequency of positive WB findings in SLE (18/73, 25%) was higher than in other diseases. ELISA kits A and B for anti-P antibodies showed 21% and 43% sensitivity, and 93% and 88% specificity, respectively, for diagnosing SLE, based on the manufacturer's cut-off values. Receiver operating characteristic (ROC) curve analysis, based on positive WB findings, determined a new cut-off threshold but revealed that both ELISA kits still had good diagnostic characteristics. In IIF assays on anti-P antibody positive sera, typical anti-P antibody cytoplasmic staining patterns (n=8) were seen less frequently than other staining patterns (n=17).


CONCLUSIONS
Routine screening for anti-P antibodies by IIF has low sensitivity. ELISAs using cut-off values established by individual facilities are suitable for detecting anti-P antibodies and provide a tool with good diagnostic characteristics, on a parity with WB.
Muro
Y
Y
Division of Connective Tissue Disease and Autoimmunity, Department of Dermatology, Nagoya University Graduate School of Medicine, Nagoya, Japan. ymuro@med.nagoya-u.ac.jp
Sugiura
K
K
Morita
Y
Y
Tomita
Y
Y
D000328:Adult; D001323:Autoantibodies / Q000032:analysis*; D015153:Blotting, Western / Q000379:methods; D003240:Connective Tissue Diseases / Q000175:diagnosis / Q000208:ethnology / Q000276:immunology*; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D010750:Phosphoproteins / Q000276:immunology*; D015995:Prevalence; D017346:Protein Serine-Threonine Kinases; D012269:Ribosomal Proteins / Q000276:immunology*; D012680:Sensitivity and Specificity
D001323:Autoantibodies; D010750:Phosphoproteins; D012269:Ribosomal Proteins; C031937:phosphoprotein P2, ribosomal; C035690:ribosomal phosphoprotein P1; C054675:ribosomal protein P0; D017346:Protein Serine-Threonine Kinases