An immunoassay differentiating sera with antibodies to Sm alone, antibodies to Sm/RNP complex, and antibodies to RNP alone.
Combined DEAE-Sephacel and hydroxyapatite chromatography resulted in a separation of free Sm antigen from the Sm/RNP complex in rabbit thymus extracts. In Western blots, the free Sm preparation contained an immunoreactive 14-kd (D) protein, whereas the Sm/RNP complex contained, in addition to the 14-kd protein, a 68-kd-reactive protein and its putative degradation fragments. Ethidium bromide staining of these preparations separated by agarose gel electrophoresis showed that the Sm/RNP preparation contained RNA, but the free Sm preparation did not. These preparations were used as antigens in an enzyme-linked immunosorbent assay (ELISA). Sera characterized as anti-Sm only, anti-Sm/RNP, and anti-RNP only were assayed. A quotient (Q) was derived from the ELISA optical density obtained with Sm/RNP as antigen divided by the optical density obtained with free Sm as antigen. Q values less than 4.0 characterized sera with anti-Sm only, values of 4.0-12.0 were observed in sera with anti-Sm plus anti-RNP, and values greater than 12.0 in sera with anti-RNP only. Sera with antibodies to other nuclear antigens were not reactive in this system. It has traditionally been difficult to identify sera with anti-RNP when this is present simultaneously with, and in lower concentration than, anti-Sm. With this method, such sera can be identified by their Q value, which falls in an intermediate region between a lower Q for anti-Sm and a higher Q for anti-RNP.
D001323:Autoantibodies / Q000032:analysis*; D001324:Autoantigens / Q000276:immunology*; D004587:Electrophoresis, Agar Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D004996:Ethidium; D006801:Humans; D007158:Immunologic Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D008947:Mixed Connective Tissue Disease / Q000276:immunology; D012261:Ribonucleoproteins / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins
D001323:Autoantibodies; D001324:Autoantigens; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins; D004996:Ethidium