Autoimmune sera reactive with Sm antigen contain high levels of RNP-like antibodies.

Abstract

Ribonucleoprotein particles containing Sm antigen were separated from particles containing both Sm and RNP antigens by ion-exchange chromatography to study the recognition of these antigens by autoimmune sera. By using the separated antigens, anti-Sm and/or anti-RNP antibodies were detected in -60% of sera from systemic lupus erythematosus patients by both enzyme-linked immunosorbent assay and immunoprecipitation of radiolabeled antigens followed by analysis on sodium dodecyl sulfate-polyacrylamide gels. These antibodies were detected in 30% of the same sera using the standard passive hemagglutination technique. Competition experiments demonstrated that all of the sera tested that contained anti-Sm antibodies also had anti-RNP-like reactivity. This latter reactivity usually represented 80% or more of the total Sm and RNP binding activity in lupus sera. The binding to RNP-like determinants by several of the sera was uniquely resistant to treatment of the antigen with snake venom exonuclease. These studies indicate that humoral immunity against Sm and RNP antigens in systemic lupus erythematosus is directed primarily against a single type of ribonucleoprotein particle in which the two antigens are physically associated. The specific binding to a single type of ribonucleoprotein particle suggests that this particle may be especially immunogenic and that it might play an important role in induction of the humoral immune response to Sm and RNP.

Distinctive immune response patterns of human and murine autoimmune sera to U1 small nuclear ribonucleoprotein C protein.

“…Immunoprecipitation of U1-C after MMB washing was restricted largely to human autoimmune sera and sera from BALB/c mice with pristane-induced autoimmunity (Table I). Out of 78 anti-nRNP/Sm (ϩ) human sera, 75 were anti-U1-C (ϩ), in agreement with previous observations that anti-Sm antibodies are usually accompanied by high levels of antinRNP antibodies (38,39). In contrast, only 1 of 65 sera from mice with spontaneous lupus was anti-U1-C (ϩ).…”

An immunoassay differentiating sera with antibodies to sm alone, antibodies to sm/RNP complex, and antibodies to RNP alone

“…In any case, our data appear to indicate that the majority (perhaps the near total) of Sm-and RNP-reactive sera will have reactivities with either the 68-kd protein or the D protein. Such evidence is supported by data from other publications (6)(7)(8)(9)(10)(19)(20)(21)(22). Another factor also makes it somewhat difficult to more precisely compare our data with those of Reeves et al (19): they did not analyze for the 68-kd protein, and this protein was the single component differentiating the Sm/RNP complex from the D protein of Sm in our study.…”

“…The assay system presented in this report is capable of distinguishing such sera from those containing anti-Sm alone and those containing anti-RNP alone. Previously, Reeves et a1 (19) had distinguished free Sm from the Sm/RNP complex by using ion exchange chromatography to analyze differences in reactivity of autoimmune sera. Their Sm and Sm/RNP preparations contained the total spectrum of traditional protein components: the Sm preparation was composed of B, B', D, E, F, and G proteins, while the Sm/RNP preparation contained, in addition, the A and C proteins.…”

Autoantibodies that stabilize the molecular interaction of Ku antigen with DNA-dependent protein kinase catalytic subunit

“…Cell extract from 2 2 10 6 cells was immunoprecipitated with 30 l of 50% (v/v) protein A-Sepharose CL4B preincubated with 10 l human autoimmune serum, 3 l rabbit anti-DNA-PK cs antiserum, or 3 l MoAb 162 ascitic fluid. Immunoprecipitates were analysed on 8% or 12 .…”