title: Identification of a linear epitope recognized by a monoclonal antibody directed to the heterogeneous nucleoriboprotein A2.
abstract: Rheumatoid arthritis (RA) is a chronic autoimmune disorder, characterized by progressive joint destruction and disability. Classical autoantibodies of RA are rheumatoid factors and citrulline antibodies. Patients positive for these autoantibodies are usually associated with a progressive disease course. A subgroup of RA patients does not express citrulline antibodies, instead are approximately 35% of these anti-citrulline-negative patients reported to express autoantibodies to the heterogeneous nucleoriboprotein A2, a ribonucleoprotein involved in RNA transport and processing also referred to as RA33. In the absence of citrulline antibodies, RA33 antibodies have been suggested to be associated with a milder disease course. In this study we screened the reactivity of a monoclonal antibody to RA33-derived peptides by modified enzyme-linked immunosorbent assays (ELISA). Terminally truncated resin-bound peptides were applied for determination of the functional epitope necessary for antibody recognition. In addition, screening of substituted peptides by modified ELISA identified amino acids necessary for antibody reactivity. A potential epitope was identified in the region 71-79 (PHSIDGRVV), where the amino acids Ser, Ile and Asp were found to be essential for antibody reactivity. These amino acids were found to contribute to the antibody-antigen interface through side-chain interactions, possibly in combination with a positively charged amino acid in position 77. Moreover, the amino acids in the N-terminal end (Pro and His) were found to contribute to the interface through backbone contributions. No notable reactivity was found with RA-positive patient sera, thus screening of RA33 antibodies does not seem to be a supplementary for the diagnosis of RA.
authors.forename: Julie
authors.initials: J
authors.lastname: Tronstrøm
authors.forename: Anette Holck
authors.initials: AH
authors.lastname: Draborg
authors.forename: Paul Robert
authors.initials: PR
authors.lastname: Hansen
authors.forename: Gunnar
authors.initials: G
authors.lastname: Houen
authors.affiliation: Department of Clinical Biochemistry, Immunology and Genetics, Statens Serum Institute, Artillerivej 5, 2300 Copenhagen S, Denmark. nhp@ssi.dk.
authors.forename: Nicole Hartwig
authors.initials: NH
authors.lastname: Trier
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology; D002956:Citrulline / Q000276:immunology; D000939:Epitopes / Q000276:immunology*; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000276:immunology*; D006801:Humans
chemical_list: D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D000939:Epitopes; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D002956:Citrulline