Ro 52kD autoantibodies are detected in a subset of ANA-negative sera

To define Ro 52kD. Ro 60 kD, and La specificities of autoantibodies within ANA-negative sera. samples from 64 ANA-negative but SSA positive patients u ndergoing investigation due to suspected CTD were analysed, using recombina nt antigens and synthetic peptides by immunoblotting and ELISA. The sera we re selected From 4025 sera submitted for routine ANA analysis. Antibodies to Ro or La were detected in 42/64 sera (65%). Anti-Re 52kD anti bodies occurred most frequently and were present in 42/64 sera (65%). This was the only specificity of autoantibody detected in 18 sera. No patient ha d only anti-La or anti-Re 60 antibodies. In total 18.64 patients (28%) had Ro 60 antibodies and 14/64 had anti-La antibodies (21%). Eight patients had antibodies reacting with all three antigens. We used the same set of sera to test the antigenicity of different regions of Ro 52kD represented by del etion clones and peptides derived from the Ro 52kD sequence. Out of 30 sera reacting with a recombinant deletion clone encompassing as residues 136-22 7, 12 sera reacted with a peptide corresponding to a 200- 239. Some sera ga ve a low positive OD value with a peptide of a 176 - 196. Based on the results of this study in which we demonstrate Ro 52kD autoanti bodies in 65% or selected ANA negative sera and define an autocephitope wit hin the Ro 52kD protein composed of the leucine zipper domain, we suggest t hat testing For Ro 52kD antibodies could be included in an extended investi gation of ANA negative patients with suspected connective tissue disease.