A sensitive and specific assay to detect Ro(SS-A) and La(SS-B) antibodies

This paper describes a sensitive and specific immunoblotting procedure to detect Ro(SS-A) and La(SS-B) autoantibodies in the serum of patients with lupus erythematosus. In order to perform this procedure, we have partially purified the Ro(SS-A) and La(SS-B) antigens from human spleen extracts by DEAE-cellulose and Sephacryl S-300 chromatography. The Ro(SS-A) and La(SS-B) antigens were immobilized on nitrocellulose paper after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tested against a panel of sera at different dilutions: normal human sera (n = 14), Ro(SS-A) antisera (n = 6), La(SS-B) (n = 7), Ro(SS-A)/La(SS-B) (n = 8), Sm-nRNP-La(SS-B) (n = 2). We found that Ro(SS-A) antisera react with a protein of an approximate Mr of 58K, whereas the La(SS-B) antisera reacted with two bands of Mr 42 and 40K, respectively. Antisera with both autoantibodies [Ro(SS-A) and La(SS-B)] reacted with both antigens, whereas the control NHS, anti-nRNP, and anti-Sm did not stain the Ro(SS-A) and La(SS-B) protein bands. In addition, some of the positive sera continued reacting with the respective antigens at extremely high dilutions. This procedure can be easily adapted to test many serum samples and produce data which include Mr of the antigen and titer of autoantibodies in the patient's serum.