title: Unmasking the anti-La/SSB response in sera from patients with Sjogren's syndrome by specific blocking of anti-idiotypic antibodies to La/SSB antigenic determinants.
abstract: BACKGROUND
  Autoantigen La/SSB is molecular target of humoral autoimmunity in patients with primary Sjogren's Syndrome (pSS) and systemic lupus erythematosus (SLE). In this study, we investigated the existence and possible influence of anti-idiotypic response to anti-La/SSB antibodies.
  
  
  METHODS
  Synthetic peptide analogs (pep) of the major antigenic determinants of La/SSB (289-308 aa and 349-364 aa) were prepared. Based on "molecular recognition" theory, complementary peptides (cpep), derived by anti-parallel readings of the noncoding strand of La/SSB DNA encoding for its antigenic determinants, were constructed. Sera from 150 patients with anti-La/SSB antibodies, 30 patients without anti-La/SSB antibodies, and 42 normal individuals were tested against all four peptides. F(ab')(2) fragments from anti-peptide IgG were prepared and F(ab')(2) - IgG interactions were evaluated using a specific anti-idiotypic ELISA.
  
  
  RESULTS
  All four peptides were recognized by anti-La positive sera (83% and 51% for pep and cpep 349-364 and 51% and 28% for pep and cpep289-308, respectively). Anti-cpep F(ab')(2 )bound to a common idiotype (Id) located within or spatially close to the antigen combining site of anti La/SSB (anti-pep) antibodies. Homologous and cross-inhibition experiments further confirmed this relation. The anti-idiotypic antibodies inhibited the anti-La/SSB antibody binding to recombinant La/SSB by 91%. To overcome the anti-idiotypic interference in anti-La/SSB detection, a specific assay was developed. Sera were heated for dissociation of Id-anti-Id complexes, anti-Id antibodies blocked with cpep, and anti-La/SSB reactivity was recovered. Application of this method to anti-Ro positive-anti-La/SSB "negative" sera showed that all anti-Ro/SSA positive autoimmune sera also possess anti-La/SSB antibodies. This reaction was not observed in 14 anti-Ro negative- anti-Sm/RNP positive sera from patients with SLE.
  
  
  CONCLUSIONS
  Autoimmune sera from patients with pSS and SLE contain anti-idiotypic antibodies targeting a common anti-La/SSB idiotype. These antibodies can be detected using complementary peptides of La/SSB epitopes. The antiidiotypic antibodies mask the anti-La/SSB response. Hidden anti-La/SSB antibodies can be released and detected using complementary epitope analogs.
authors.affiliation: Department of Pathophysiology, School of Medicine, National University of Athens, Greece.
authors.forename: John G
authors.initials: JG
authors.lastname: Routsias
authors.forename: Evgenia
authors.initials: E
authors.lastname: Touloupi
authors.forename: Eleni
authors.initials: E
authors.lastname: Dotsika
authors.forename: Avrilia
authors.initials: A
authors.lastname: Moulia
authors.forename: Vassilios
authors.initials: V
authors.lastname: Tsikaris
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sakarellos
authors.forename: Maria
authors.initials: M
authors.lastname: Sakarellos-Daitsiotis
authors.forename: Haralampos M
authors.initials: HM
authors.lastname: Moutsopoulos
authors.forename: Athanasios G
authors.initials: AG
authors.lastname: Tzioufas
mesh_terms: D000595:Amino Acid Sequence; D000888:Antibodies, Anti-Idiotypic / Q000097:blood / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D001324:Autoantigens; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000276:immunology; D016372:RNA, Antisense / Q000235:genetics; D012261:Ribonucleoproteins / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000097:blood / Q000276:immunology*; D000097585:SS-B Antigen
chemical_list: D000888:Antibodies, Anti-Idiotypic; D001323:Autoantibodies; D001324:Autoantigens; D010455:Peptides; D016372:RNA, Antisense; D012261:Ribonucleoproteins; D000097585:SS-B Antigen