title: Serological epitope profile of anti-Ro52-positive patients with systemic autoimmune rheumatic diseases.
abstract: BACKGROUND
  Ro52 is an interferon-inducible protein of the tripartite motif family. Antibodies against Ro52 have been described in patients with different autoimmune diseases, such as systemic lupus erythematosus and Sjögren's syndrome, that are often associated with anti-Ro60 antibodies. The Ro52 autoantigen is extraordinarily immunogenic, and its autoantibodies are directed against both linear and conformational epitopes. The aim of this study was to evaluate the prevalence of antibodies to the five Ro52 domains, as well as to Ro52 176- to 196-amino acid (aa) and 200-239-aa peptides, in different systemic autoimmune rheumatic diseases (SARDs). We also aimed to verify whether antibodies to a single domain or domain association could increase their diagnostic specificity for any SARD.
  
  
  METHODS
  Serum samples were obtained from 100 anti-Ro52 antibody-positive patients with SARDs and from 68 controls (50 healthy donors and 18 patients with other autoimmune or allergic diseases). A special line immunoassay was created containing a full-length Ro52 antigen expressed in insect cells using the baculovirus system, five recombinant Ro52 antigen fragments [Ro52-1, Ro52-2, Ro52-3, Ro52-4 (partly overlapping Ro52-1 and Ro52-2), and Ro52-5 (partly overlapping Ro52-2 and Ro52-3)], and two Ro52 peptides (176-196 aa and 200-239 aa), all expressed in Escherichia coli.
  
  
  RESULTS
  In patients with SARDs, fragment prevalence rates were as follows: Ro52-1 = 3 %, Ro52-2 = 97 %, Ro52-3 = 0 %, Ro52-4 = 9 %, Ro52-5 = 28 %, Ro52 175-196-aa peptide = 6 %, and Ro52 200-239-aa peptide = 74 %. All control samples were negative for the full-length Ro52 and for the five fragments tested.
  
  
  CONCLUSIONS
  The main epitope of the Ro52 antigen was localized on fragment 2 (aa 125-267), and the majority (97 %) of SARD sera had antibodies that target this fragment. As most of the samples were positive for fragment 2 and only some for fragments 4 or 5, which partially overlap fragment 2, it seems that the target epitope is localized in the middle of fragment 2 or in the area between fragments 4 and 5. No antibody against a single epitope or a combination of epitopes was linked to any of the single SARDs.
authors.affiliation: SOS Laboratorio Immunologia e Allergologia, Ospedale S. Giovanni di Dio, Via Torregalli 3, 50143, Firenze, Italy. maria2.infantino@asf.toscana.it.
authors.forename: Maria
authors.initials: M
authors.lastname: Infantino
authors.affiliation: SOS Laboratorio Immunologia e Allergologia, Ospedale S. Giovanni di Dio, Via Torregalli 3, 50143, Firenze, Italy. francesca.meacci@asf.toscana.i.
authors.forename: Francesca
authors.initials: F
authors.lastname: Meacci
authors.affiliation: SOS Laboratorio Immunologia e Allergologia, Ospedale S. Giovanni di Dio, Via Torregalli 3, 50143, Firenze, Italy. valentinagrossi2@virgilio.it.
authors.forename: Valentina
authors.initials: V
authors.lastname: Grossi
authors.affiliation: SOS Reumatologia, Ospedale S. Giovanni di Dio, Firenze, Italy. maurizio.benucci@asf.toscana.it.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Benucci
authors.affiliation: Dipartimento di Scienze Mediche Chirurgiche e Neuroscienze, Policlinico Le Scotte, Siena, Italy. morozzi@unisi.it.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Morozzi
authors.affiliation: Immunopatologia e Allergologia, Azienda Ospedaliero-Universitaria, Udine, Italy. tonutti.elio@aoud.sanita.fvg.it.
authors.forename: Elio
authors.initials: E
authors.lastname: Tonutti
authors.affiliation: Laboratorio di Patologia Clinica, Policlinico Universitario, Bari, Italy. mtampoia@libero.it.
authors.forename: Marilina
authors.initials: M
authors.lastname: Tampoia
authors.affiliation: Euroimmun AG, Luebeck, Germany. n.ott@euroimmun.de.
authors.forename: Antonina
authors.initials: A
authors.lastname: Ott
authors.affiliation: Euroimmun AG, Luebeck, Germany. w.meyer@euroimmun.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Meyer
authors.affiliation: UOC Reumatologia, Ospedale L. Sacco Polo Universitario, Milano, Italy. atzenifabiola@hotmail.com.
authors.forename: Fabiola
authors.initials: F
authors.lastname: Atzeni
authors.affiliation: UOC Reumatologia, Ospedale L. Sacco Polo Universitario, Milano, Italy. sarzi@tiscali.it.
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Sarzi-Puttini
authors.affiliation: SOS Laboratorio Immunologia e Allergologia, Ospedale S. Giovanni di Dio, Via Torregalli 3, 50143, Firenze, Italy. mariangela.manfredi@asf.toscana.it.
authors.forename: Mariangela
authors.initials: M
authors.lastname: Manfredi
authors.affiliation: Laboratorio di Patologia Clinica, Ospedale San Antonio, Tolmezzo, Italy. nicola.bizzaro@aas3.sanita.fvg.it.
authors.forename: Nicola
authors.initials: N
authors.lastname: Bizzaro
mesh_terms: D000595:Amino Acid Sequence; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology*; D001327:Autoimmune Diseases / Q000097:blood* / Q000276:immunology*; D000939:Epitopes; D006801:Humans; D007118:Immunoassay; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology; D012261:Ribonucleoproteins / Q000276:immunology*; D000099207:SS-A Antigen
chemical_list: D001323:Autoantibodies; D000939:Epitopes; D010455:Peptides; D012261:Ribonucleoproteins; D000099207:SS-A Antigen