Autoimmune sera react with multiple epitopes on recombinant 52 and 60 kDa Ro(SSA) proteins

To determine the reactivity of recombinant 52 and 60 kDa Ro(SSA) (Ro) proteins with sera from 3 subsets of patients with Ro autoantibody associated disease.

Complementary DNA (cDNA) clones that encode the human 52 and 60 kDa Ro autoantigens were isolated by the polymerase chain reaction and utilized to express recombinant glutathione S-transferase (GST) fusion proteins. Double immunodiffusion (ID) defined Ro positive autoimmune sera from 12 patients with neonatal lupus erythematosus (NLE), 16 with subacute cutaneous lupus erythematosus (SCLE) and 12 with primary Sjögren's syndrome (SS) were tested by enzyme linked immunosorbent assay (ELISA) against the recombinant 52 and 60 kDa Ro fusion proteins.

Seventy-five percent of NLE, 56% of SCLE and 83% of SS sera reacted with the 52 kDa fusion protein. Seventy-five percent of NLE, 63% of SCLE and 83% of SS sera reacted with the 60 kDa fusion protein. Seventeen percent of NLE sera, 25% of SCLE sera and 8% of SS sera were nonreactive to both full length fusion proteins. Eight (57%) of 14 ID defined Ro negative NLE, SCLE and SS sera were reactive with both Ro fusion proteins by ELISA: ELISA studies with recombinant 52 and 60 kDa Ro protein fragments revealed at least 2 major epitopes on each Ro protein. A fragment of the 52 kDa Ro protein that contains a putative leucine zipper motif reacted with 100% of ID defined Ro positive SS sera.

Our data demonstrate that the ID assay and the recombinant Ro ELISA together are more sensitive in detecting Ro antibodies than either assay alone, and that multiple epitopes are present on both Ro proteins.