title: Preferential recognition of the phosphorylated major linear B-cell epitope of La/SSB 349-368 aa by anti-La/SSB autoantibodies from patients with systemic autoimmune diseases.
abstract: Sera from patients with primary Sjögren Syndrome (pSS) or Systemic Lupus Erythematosus (SLE) often contain autoantibodies directed against La/SSB. The sequence 349-368 aa represents the major B-cell epitope of La/SSB, also it contains, at position 366, a serine amino acid residue which constitutes the main phosphorylation site of the protein. In this study we investigated the differential recognition of the 349-368 aa epitope and its phosphorylated form by antibodies found in sera from patients with systemic autoimmune diseases. Peptides corresponding to the sequence of the unphosphorylated (pep349-368 aa) and the phosphorylated form (pep349-368 aa Ph) of the La/SSB epitope 349-368 aa, as well as to a truncated form spanning the sequence 349-364 aa and lacking the phosphorylation site (pep349-364 aa), were synthesized. Sera from 53 patients with pSS and SLE with anti-La/SSB specificity, 30 patients with pSS and SLE without anti-La/SSB antibodies, 25 patients with rheumatoid arthritis and 32 healthy individuals were investigated by ELISA experiments. Autoantibodies to pep349-368 aa Ph were detected in sera of anti-La/SSB positive patients with a higher prevalence compared to the pep349-368 aa (66%versus 45%). Pep349-368 aa Ph inhibited the antibody binding almost completely (92%), while pep349-368 aa inhibited the binding only partially (45%). Anti-La/SSB antibodies presented a higher relative avidity for the phosphorylated than the unphosphorylated peptide. Immunoadsorbent experiments using the truncated peptide pep349-364 aa indicated that the flow through showed a selective specificity for pep349-368 aa Ph, while the eluted antibodies reacted with both peptide analogues of the La/SSB epitope. These data suggest that sera from pSS and SLE patients with anti-La/SSB reactivity possess autoantibodies that bind more frequently and with a higher avidity to the phosphorylated major B-cell epitope of the molecule.
authors.affiliation: Department of Pathophysiology, School of Medicine, University of Athens, Athens, Greece.
authors.forename: A G
authors.initials: AG
authors.lastname: Terzoglou
authors.forename: J G
authors.initials: JG
authors.lastname: Routsias
authors.forename: S
authors.initials: S
authors.lastname: Avrameas
authors.forename: H M
authors.initials: HM
authors.lastname: Moutsopoulos
authors.forename: A G
authors.initials: AG
authors.lastname: Tzioufas
mesh_terms: D000915:Antibody Affinity; D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000737:chemistry / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D018985:Epitopes, B-Lymphocyte / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D007163:Immunosorbent Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology; D010766:Phosphorylation; D012261:Ribonucleoproteins / Q000737:chemistry / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000276:immunology; D000097585:SS-B Antigen
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D018985:Epitopes, B-Lymphocyte; D010446:Peptide Fragments; D012261:Ribonucleoproteins; D000097585:SS-B Antigen