The line immunoassay (LIA) for the determination of antibodies to individual extractable antinuclear antigens (ENA) is a development of the enzyme-linked immunosorbent assay (ELISA) in which the antigens to be tested are adsorbed onto a nylon test strip. In addition, the antigen subspecificities B/B' and D in the case of Sm, the 70 kD, A and C components in the case of U1-snRNP and the Ro52 and Ro60 components in the case of SSA/Ro are present separately on the strips. The aim of the study was to determine whether the line immunoassay is suitable for routine laboratory use by means of a comparison with the ELISA.
Sera from 92 patients stored in our serum bank with known ENA profile as determined by ELISA and with at least one antibody to ENA were tested again with LIA. The clinical features and other available laboratory data taken from the patient records were used to classify the disease according to the relevant diagnostic criteria. In discrepant cases, antibodies to ENA were also determined by Western blot. These data were used to determine which of the two methods gave the more plausible results and to calculate the sensitivity and specificity for each autoantibody.
There was good correlation between the two methods, especially for anti-CENP-B (centromere protein B) and anti-Jo1 (histidyl-tRNA transferase) antibodies. For anti-Sm, there was a trend toward higher specificity with the LIA in patients with systemic lupus erythematosus (SLE) if antibodies to Sm D were detected. The LIA was significantly more specific for the detection of antibodies to ribonucleoprotein (RNP) in mixed connective tissue disease and, if antibodies to the 70 kD component were present, also in SLE, although the sensitivity was significantly lower in this case. For anti-SSA/Ro, the specificity of the LIA was significantly higher than ELISA if anti-Ro60 was detected. In the case of anti-SS-B/La, anti-Scl70 (topoisomerase I), anti-CENP-B (centromere protein B) und anti-Jo-1 (histidyl-tRNA transferase), the sensitivity and specificity of the two methods were not significantly different. The LIA was significantly more specific but less sensitive for the detection of anti histone antibodies.
The suitability of the LIA for routine laboratory determinations was confirmed.