Human autoantibodies directed against the RNA recognition motif of La (SS-B) bind to a conformational epitope present on the intact La (SS-B)/Ro (SS-A) ribonucleoprotein particle.
In systemic autoimmunity, the human B cell response to the La (SS-B) autoantigen is polyclonal and directed to both conserved and human-specific epitopes. This study has further characterized the B cell epitope(s) present within the conserved central region of the La protein, LaC (amino acids 111-242) containing the RNA recognition motif (RRM, aa 111-187). Ten overlapping and non-overlapping protein fragments spanning LaC were expressed in bacteria as NH2-terminal fusions with glutathione-S-transferase. The fusion proteins were tested by ELISA for reactivity with a panel of human anti-La sera in order to define the nature of the epitopes. Ninety-two percent of patient sera containing anti-La antibodies reacted with the region of La containing the RRM. Fine mapping of this reactivity using deletion mutants indicated that the deletion of 19 amino acids from either the NH2-terminal or COOH-terminal region of the RRM was associated with loss of antibody reactivity, suggesting that the immunodominant epitope expressed in this region is discontinuous. Autoantibodies affinity-purified from the La RRM fragment to remove other specificities immunoprecipitated newly synthesized native La (SS-B)/Ro (SS-A) complexes, providing additional evidence that autoantibodies were recognizing a conformational epitope. The findings indicate that the human autoantibody response to La involves recognition of a conformational determinant involving the conserved RRM region without necessarily interfering with the RNA-dependent association of the La/Ro ribonucleoprotein.
Rischmueller
M
M
Centre for Transfusion Medicine and Clinical Immunology, Flinders Medical Centre, Bedford Park, South Australia.
McNeilage
L J
LJ
McCluskey
J
J
Gordon
T
T
D001323:Autoantibodies / Q000276:immunology* / Q000378:metabolism; D001324:Autoantigens / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D018604:Epitope Mapping / Q000592:standards; D000939:Epitopes / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D020733:RNA, Small Cytoplasmic; D012261:Ribonucleoproteins / Q000276:immunology* / Q000378:metabolism; D014157:Transcription Factors / Q000276:immunology / Q000378:metabolism; D000097585:SS-B Antigen; D000099207:SS-A Antigen
D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D020733:RNA, Small Cytoplasmic; D012261:Ribonucleoproteins; D014157:Transcription Factors; D000097585:SS-B Antigen; D000099207:SS-A Antigen; C116006:RO60 protein, human