Comparison of assay systems for detecting antibodies to nuclear ribonucleoproteins

The specificity and sensitivity of two commercial enzyme linked immunosorbent assays (ELISAs), Diamedix (Miami, Florida) and Lipogen (Noxville, Tennessee), were assessed and compared with haemagglutination and immunodiffusion assays. Sera from 53 patients with various connective tissue disorders were examined for the presence of antibodies to nuclear antigens (ANA), double stranded DNA (dsDNA), Sm, RNP, SSA/Ro, and SSB/La. Of the 53 patients, 42 were ANA positive, 11 were ANA negative, and 22 had antibodies to dsDNA. Seven patients had antibodies to Sm by haemagglutination assay; these were also positive in both ELISA systems (only five of the seven patients were assayed by the Lipogen ELISA system). Two additional Sm positive values were obtained in each of the ELISA systems but only one of these was positive in both. Ten positive RNP results were obtained by haemagglutination and nine of these were also positive by the Diamedix ELISA. Only eight samples were tested by the Lipogen assay and seven of these were positive. Three additional RNP positive values were obtained by the Diamedix and six by the Lipogen ELISA assays. Of these, only two were positive in both. Antibodies to SSA/Ro were obtained in 11 patients by immunodiffusion and lines of partial identity were observed in nine. SSB/La antibodies were positive in six patients and two had lines of partial identity. All the SSA/Ro and SSB/La positive sera were also positive in both ELISA systems. Moreover, eight additional SSA/Ro positive values were obtained in each of the ELISAs, four of which had partial identity lines in the immunodiffusion assay. Furthermore, three additional SSB/La positive values were obtained by the Diamedix and four by the Lipogen assays. Of these, only two were positive in both ELISAs. This study shows that the above ELISAs are comparable in specificity and sensitivity with haemagglutination assay for detection of antibodies to Sm and RNP antigens and are more sensitive than immunodiffusion for the detection of SSA/Ro and SSB/La antigens.