Purification and Characterization of a Nuclear SS‐B Antigen

Abstract

A nuclear SS-B antigen was isolated from a saline extract of acetone powder of rabbit thymus by precipitation with (NH4)2SO4, affinity chromatography with Blue Sepharose CL-6B and preparative agarose gel electrophoresis. The MW of the antigen was 68,000. Its electrophoretic mobility was similar to that of pre-albumin and the isoelectric point was .apprx. pH 4.0. The main amino acids of the antigen were glutamic acid, leucine, lysine and alanine. Both histidine and tyrosine were also found. The purified antigen precipitated with anti-SS-B sera but not with any other reference antisera. It resembled La and Ha antigens in susceptibility to proteolytic and nucleolytic enzymes and to heat. The purified SS-B antigen had a higher MW than did the Ha and La antigens. The molecule could not be split into subunits with mercaptoethanol or acid. Counter-electrophoresis showed antibodies to the SS-B antigen in sera from patients with rheumatic diseases, including rheumatoid arthritis, systemic lupus erythematosus and Sjogren''s syndrome, but not in any of the control sera.