The fine specificity of anti-La antibodies induced in mice by immunization with recombinant human La autoantigen

Because of increasing evidence suggesting that anti-La autoantibodies are induced in humans by an Ag-specific mechanism, we investigated the antibody response of animals immunized with the human La Ag and studied its relationship to the anti-La response of autoimmune patients. Anti-La antibodies were raised in 6- to 8-wk-old male MRL(-)+/+, C57BL/6J, BALB/c, and A/J mice by immunizing with authentic human La protein obtained by recombinant expression in Escherichia coli. As we have shown previously for human autoantibodies, induced mouse anti-La antibodies reacted with recombinant fusion proteins containing nonoverlapping sequences from different portions of the La molecule. The epitope specificity of antibodies to the middle region of the La Ag was further evaluated using six synthetic La peptides predicted to be antigenic based on their hydrophilic properties. Although the induced mouse anti-La antibodies bound to five of the six synthetic La peptides, human anti-La autoantibodies failed to recognize any of the peptide homologs. These results suggest that mice respond to immunization with human La protein differently than humans who develop autoimmunity to this self Ag.