Antigenicity of a recombinant Ro (SS-A) fusion protein

The antigenicity of the 60-kd human Ro (SS-A) synthesized in vitro from its complementary DNA as a beta-galactosidase fusion protein (beta-gal-Ro) was evaluated by Western blotting. In this analysis, almost all the anti-Ro (SS-A)-positive sera that bound beta-gal-Ro also bound affinity-purified 60-kd human Ro (SS-A) (P less than 0.005). Three of the 27 anti-Ro (SS-A) precipitin-positive sera, however, did not show reactivity on Western blot analysis, which suggests that in some sera, antigenicity to Ro (SS-A) is destroyed by denaturation. Of the 22 sera that were reactive with beta-gal-Ro, 2 were not reactive with affinity-purified human Ro (SS-A). Two serum samples that did not react with beta-gal-Ro were also reactive with affinity-purified human Ro (SS-A). Nevertheless, except for a small percentage of Ro (SS-A) precipitin-positive sera, the frequency of antibody binding to the fusion protein was similar to the frequency of binding to the purified antigen in Western blots. Recombinant Ro (SS-A) antigen may therefore be valuable in the serologic evaluation of anti-Ro (SS-A) autoantibodies.