Properties of the ribosomal P2 protein autoantigen are similar to those of foreign protein antigens.

Approximately 15% of patients with systemic lupus erythematosus have autoantibodies that bind to a shared epitope previously shown to be located on the carboxyl-terminal 22 amino acids of three 60S ribosomal proteins, P0, P1, and P2 ("P proteins"). A hydrophilicity plot and fine epitope mapping with seven synthetic peptides revealed that the properties of the antigenic site were similar to certain properties of epitopes on foreign protein antigens--namely, the epitope was located in the most hydrophilic portion of the P2 protein and also in the terminal region of the molecule. However, this site has been highly conserved during evolution. A mouse monoclonal antibody induced by immunization with ribosomal proteins had a fine specificity similar to the lupus antibodies. This finding indicates that a highly conserved region of a lupus autoantigen may also be antigenic in some normal animals. Therefore, lupus autoantibodies may be similar in most, if not all respects, to antibodies produced by immunization.