RECOMBINANT 52 KDA RO(SSA) ELISA DETECTS AUTOANTIBODIES IN SJOGRENS-SYNDROME SERA THAT GO UNDETECTED BY CONVENTIONAL SEROLOGIC ASSAYS

Objective. To determine the utility of a recombinant 52 kDa Ro(SSA) EL ISA for detecting Ro autoantibodies in Sjogren's syndrome (SS) sera. M ethods. Several different groups of SS sera previously tested for Ro a nd La(SSB) autoantibodies in clinical diagnostic labs were tested by E LISA with a recombinant human 52 kDa Ro fusion protein. Results. Five of 18 primary SS sera (28%) that had undetectable Ro and La autoantibo dies by conventional immunodiffusion (ID) or ELISA in clinical diagnos tic laboratories had significant reactivity with a recombinant 52 kDa Ro (r52) ELISA. On repeat testing these 5 sera were again negative for Ro and La antibodies by ELISA with purified 60 kDa Ro and La antigens , but 3 of these sera were reactive with r52 by immunoblot, and immuno precipitated a 52, kDa protein from human cell extracts. Twelve of 12 primary SS sera that had detectable Ro autoantibodies by ID also react ed with the r52 ELISA, whereas none of 11 normal sera and only one of 27 ID-defined Ro negative systemic lupus erythematosus sera did, Eleve n of 28 sera from patients with suspected SS were Ro positive by ID an d 60 kDa Ro ELISA. All 11 were also Ro positive by the r52 ELISA, Two or the 28 suspected SS sera were Ro positive by the r52 Ro ELISA, but were Ro and La negative by to and 60 kDa Ro and La ELISA. Conclusions. Anti-52 kDa Ro autoantibodies are frequently present in primary SS se ra, but may go undetected by commonly used Ro serologic assays. Our r5 2 ELISA is more sensitive in detecting Ro antibodies in SS than conven tional ID and 60 kDa Ro ELISA.