A MAJOR, NOVEL SYSTEMIC LUPUS-ERYTHEMATOSUS AUTOANTIBODY CLASS RECOGNIZES THE E-SM, F-SM, AND G-SM SNRNP PROTEINS AS AN E-F-G COMPLEX BUT NOT IN THEIR DENATURED STATES

Objective. To determine whether the E, F, and G Sm proteins present an tigenic determinants recognized by systemic lupus erythematosus (SLE) patient sera, and if so, whether the antigenicity depends on the nativ e conformations of the polypeptides and/or is E-F-G complex restricted . Methods. Radioimmunoprecipitation, epitope tagging, expression polym erase chain reaction, in vitro translation, in vitro reconstitution, a nd immunoblotting.Results. Most of the anti-Sm SLE patient sera tested reacted with one or more of the E, F, and G proteins in immunoprecipi tation studies but not on immunoblots, All sera, however, highly effic iently immunoprecipitated the E-F-G complex, This complex recognition was detected exclusively in anti-Sm patient sera but not in patient se ra with other serotypes. Conclusion. We demonstrate the presence of a novel and abundant anti-Sm autoantibody class in SLE patient sera whic h exclusively or predominantly recognizes conformational Sm epitopes p resent on the E-F-G complex but not on the denatured proteins, This co mplex recognition is highly specific for sera of the anti-Sm serotype and may be relevant for clinical diagnosis as well as for understandin g the etiology of anti-Sm autoantibody production.