Unmasking of anti-ribosomal P autoantibodies in healthy individuals.

Autoantibodies to the ribosomal P proteins (anti-P) are found almost exclusively in a subset of patients with systemic lupus erythematosus. To determine if anti-P autoantibodies are present in healthy individuals but in a masked state, sera from healthy adults were applied to affinity columns coated with ribosomes, and the affinity-purified fractions were analyzed for anti-P Abs by ELISA and immunoblot. Anti-P Abs were detectable in serum only after affinity chromatography, were predominantly of the IgG isotype, stained HEp-2 cells in the characteristic anti-P pattern, and demonstrated specificity for all three ribosomal P phosphoproteins. Using batch affinity chromatography, we identified anti-P autoantibodies in the affinity-purified serum fractions of 54 of 55 healthy individuals. Anti-P Abs from healthy adults generally bound less ribosomal P Ag per mg/ml IgG than anti-P from patients. Inhibition studies revealed that autologous serum contained an IgG inhibitor of anti-P Ab. We conclude that masked anti-P autoantibodies are present in the healthy population and hypothesize that detection of these autoantibodies in systemic lupus erythematosus represents disruption of these regulatory networks.