title: Definition of a discontinuous immunodominant epitope at the NH2 terminus of the La/SS-B ribonucleoprotein autoantigen.
abstract: High-titer IgG autoantibodies to the La/SS-B ribonucleoprotein (RNP) are a hallmark of patients with primary Sjogren's syndrome. Anti-La/SS-B-positive human sera bind to multiple epitopes on recombinant La/SS-B, although the initial response is against an immunodominant epitope within the first 107 NH2-terminal amino acids (aa). Sequence analysis has identified a striking homology between aa 88-101 in this NH2-terminal region of La/SS-B and a feline retroviral gag polypeptide suggesting the anti-La/SS-B response may be initiated by cross-reactivity with an exogenous agent. In the present study, detailed mapping of this NH2-terminal epitope, using recombinant La/SS-B purified from the expression of overlapping DNA fragments spanning aa 1-107, has shown that this immunodominant epitope is a complex conformational or discontinuous epitope dependent upon both aa 12-28 and 82-99 for expression, even though these regions share no homology with each other. This requirement questions the significance of the homology between La/SS-B and a retroviral gag polypeptide in the generation of the B cell response to La/SS-B and is in accord with the general concept that B cells recognize conformational epitopes on antigens rather than small linear peptide sequences. The finding also reinforces the notion that native autoantigen could be the initiator of the autoimmune response.
authors.affiliation: Department of Clinical Immunology, Flinders Medical Centre, Bedford Park, South Australia.
authors.forename: L J
authors.initials: LJ
authors.lastname: McNeilage
authors.forename: K
authors.initials: K
authors.lastname: Umapathysivam
authors.forename: E
authors.initials: E
authors.lastname: Macmillan
authors.forename: A
authors.initials: A
authors.lastname: Guidolin
authors.forename: S
authors.initials: S
authors.lastname: Whittingham
authors.forename: T
authors.initials: T
authors.lastname: Gordon
mesh_terms: D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000737:chemistry / Q000276:immunology*; D001483:Base Sequence; D001667:Binding, Competitive; D000939:Epitopes; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010455:Peptides / Q000276:immunology; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000276:immunology; D012261:Ribonucleoproteins / Q000737:chemistry / Q000276:immunology*; D000097585:SS-B Antigen
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D009838:Oligodeoxyribonucleotides; D010455:Peptides; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D000097585:SS-B Antigen