Evaluation of recombinant Ro/SSA, La/SSB, Sm, and U1 RNP autoantigens in clinical diagnosis

This study comprises an analysis of the diagnostic usefulness of Ro/SSA, La/SSB, Sm and U1 RNP autoantigens obtained by DNA recombinant technology. We studied the presence of these autoantibodies in 33 patients with systemic lupus erythematosus (SLE) and 30 normal individuals by enzyme-linked immunosorbent assay (ELISA) using recombinant autoantigens and by Western immunoblot with these same antigens obtained from natural sources (rabbit thymus and human spleen). The strength of agreement between results found with these two techniques was moderate in the case of anti-Ro/SSA (kappa = 0.474, P < 0.001) and anti-U1 RNP (kappa = 0.566. P < 0.001) antibodies and almost perfect in the case of anti-La/SSB (kappa = 0871, P < 0.001) and anti-Sm (kappa = 0.833, P < 0.001). Furthermore, analysis of the disagreement between the two techniques evidenced a measurement bias for anti-Ro/SSA and anti-U1 RNP antibodies (Mc NEMAR'S statistic 13 and 11, respectively) whose direction, though difficult to define in the absence of a gold standard for such determinations, could be accounted for by the ELISA technique's greater tendency to produce positive results. Our conclusion is that the diagnostic usefulness of recombinant La/SSB and Sm autoantigens has been satisfactorily proven, whereas the case of the Ro/SSA and U1 RNP systems should be subject to further in-depth study of the autoepitopes recognised and the possible modifications which the latter might undergo as a result of their obtension from procariotic sources.