SYSTEMIC LUPUS-ERYTHEMATOSUS IS ASSOCIATED WITH INCREASED AUTOANTIBODY TITERS AGAINST CALRETICULIN AND GRP94, BUT CALRETICULIN IS NOT THE RO SS-A ANTIGEN/

Auto-antibodies against purified human calreticulin were determined by an ELISA in sera from patients with systemic lupus erythematosus (SLE ) and from healthy persons or patients without an autoimmune disease. More than 80% of patients with SLE had titers exceeding the highest va lue obtained in the group without SLE. Almost 30% of the patients had also elevated auto-antibody titers against purified rat grp94, another resident ER-protein of the KDEL-protein family, but not against rat E Rp72 (CaBP2), an ER-resident protein of the proteindisulfide isomerase family. It could, however, be excluded that calreticulin is the Ro/SS -A antigen on the basis of the following observations: 1) Calreticulin purified from rat, bovine or human liver contained far less than 1 me l of phosphate per mol of calreticulin, showed an E280/E260-absorption ratio of about 2.0, and did not contain extractable RNA; 2) Sera from patients with SLE did not react with or precipitate endogenous calret iculin from Hep G2 cells; they did, however, precipitate hY-RNA from t hese cells; 3) Sera from SLE-patients, but not anti-calreticulin antis era precipitated [P-32]-hY-RNA from [P-32]-labelled Hep G2 cells.