[Detection of anti small nuclear ribonucleoprotein antibody in patients with collagen disease--a comparison of sensitivities of four methods].

OBJECTIVE

To compare the sensitivity of four techniques that can detect the presence of anti small nuclear ribonucleoprotein (snRNP) antibodies.

MATERIAL AND METHOD: Sera from eighty three patients with connective tissue disease were positive for antinuclear antibody by indirect immunofluorescence test. Patients consisted of 30 cases of systemic lupus erythematosus, 19 of rheumatoid arthritis, 9 of mixed connective tissue disease, 8 of systemic sclerosis, 3 of polymyositis, 13 of Sjögren syndrome, 1 of unclassified connective tissue disease. Four methods including double immunodiffusion (DID), enzyme linked immunosorbent assay (EIA), immunoprecipitation (IP) and immunoblotting (IB) were compared concerning their sensitivities of detecting anti-Sm and anti-RNP antibodies in these sera.

RESULTS

Overall sensitivities for detecting the presence of each antibody were similar among four methods (DID: 32/83, EIA: 43/83, IP: 44/83, IB: 35/83). Concordance ratio of positive patterns between DID and EIA was 63/83 (81.9%). However, both EIA and IP could detect anti-U1 RNP antibody with higher sensitivity than DID. Although EIA seemed to detect anti-Sm antibody most sensitively in all methods, a coincidental decrease of specificity might be considered. IB could not classify anti-snRNP antibodies into anti-Sm and/or anti-RNP antibody because these antibodies might share some antigenic peptides of snRNP. Analysis of RNA in immunoprecipitate could not discriminate anti-RNP antibodies from anti-Sm antibodies because of shared RNA epitopes (e.g., U1-RNA, U1U2-RNA).

CONCLUSION

These results suggested that EIA might be the most suitable method for detecting anti-RNP antibody and that several methods should be combined for detecting anti-Sm antibody.