Immunological characterization of small nuclear ribonucleoproteins reactive with sera of patients with systemic lupus erythematosus.

We have previously reported the purification of Sm and RNP antigens from goat liver and identified two polypeptides of molecular weights 70 and 80-90 kd as RNP specific and of 14 and 30 kd as Sm specific. In this communication the effect of ribonuclease and trypsin on Sm and RNP antigens was studied at the polypeptide level. We found that the RNP antigenic determinant polypeptides of 70 and 80-90 kd are lost as a result of such treatment, whereas there is no effect on the Sm-specific 14- and 30-kd polypeptides. The role of RNA in the antigenicity of Sm and RNP was studied by dissociation and reconstitution studies. The antigens were fractionated into protein and RNA and the individual fractions were tested for Sm and RNP activity by counterimmunoelectrophoresis (CIE) and enzyme-linked immunosorbent assay (ELISA). The RNA fraction did not react alone with anti-Sm and anti-RNP sera with either of the assays. Conversely when the protein fraction was tested by CIE, only Sm antigenicity was detectable. In the ELISA both Sm and RNP activities were demonstrated in the protein fraction. These results show that the presence of RNA is important in the immunoprecipitation reactions involving only RNP antigen, whereas Sm activity is independent of RNA. In addition, when the reaction is carried out by an assay involving primary antigen-antibody reaction (e.g., ELISA), RNP antibodies react with protein fractions alone, without the presence of RNA. We also report the glycoprotein nature of Sm-specific polypeptides.(ABSTRACT TRUNCATED AT 250 WORDS)