A solid-phase radioimmunoassay for the detection of anti-ribosome antibodies is described. Only small quantities of ribosomal particles are required, and low levels of antibody can be detected by very simple procedures. This assay has been used to detect antibodies which bind to intact ribosomes and to isolated large (603 and small (40s) ribosomal subunits. The antibodies were present in sera from patients with systemic lupus erythematosus (SLE) and reacted predominantly with the 60s subunits. The potential use of the assay for the study of ribosome structure is discussed.
Autoantibodies
which react with ribosomes from human and animal sources have been detected in the sera of patients with systemic lupus erythematosus (SLE) by several methods. Immunodiffusion was used by several authors (10,l l), and the incidence of sera which contained ribosomal antibodies was approximately 13%. Bentonite particles coated with ribosomes were used in a flocculation test (12) which showed 23% positive reactors in SLE. Other methods, including a fluorescent spot test (10,ll) have detected ribosomal antibodies in up to 50% of SLE sera. Antibodies in these sera did not react with ribosomes which had been treated with trypsin or RNase, indicating that both protein and RNA moieties were involved in the antigenic determinants. When SLE sera were analyzed by immunofluorescence on sections of human and animal tissues, ribosomal antibodies were detected in less than 1% of SLE patients (1,13). These sera did not fix complement with ribosomes which had been hydrolyzed by trypsin but did so with RNase-treated ribosomes. Treatment of tissue sections with RNase did not abolish the binding of these SLE antibodies. This led to the conclusion that most of the ribosomal antibodies detected by immunofluorescence in these sera were directed against protein and not RNA structures.
Human autoantibodies react with fewer determinants than sera of animals immunized with the help of Freunds' adjuvant (1). The present investigation was undertaken to ascertain whether the ribosomal antibodies detected by immunofluorescence in SLE sera reacted with one or both ribosomal subunits. For this purpose, we have modified the solid-phase radioimmunoassay procedure of Hay et al.
(2) for use with 217