AB0055 AUTOIMMUNE RESPONSE AGAINST THE SHARED EPITOPE SEQUENCE IN RHEUMATOID ARTHRITIS
Authors: E. Graell, J. F. Delgado de la Poza, A. D. Gomez Centeno, M. Garcia Manrique de Lara, M. J. Amengual Guedan, E. Nuez Zaragoza, M. Aliste Fernandez, S. Rodriguez Navarro, M. Arevalo Salaet, S. Garcia-Cirera, M. Rusiñol, E. Costa Moya, C. Orellana, J. Calvet Fontova, M. Moreno Martinez-Losa, E. Casado, C. Galisteo, N. Navarro, M. Llop Vilaltella, J. Gratacos Masmitjà
Journal: Annals of the Rheumatic Diseases (2021)

Background: Rheumatoid Arthritis (RA) is a systemic autoimmune disease, associated with hiperproduction of autoantibodies (AAb), in which the most specific are the AAb against citrullinated peptides (ACPA). RA is influenced by genetic factors, specifically, there is a strong genetic association with the shared epitope (SE), a five amino acid sequence motif in positions 70–74 of HLA-DRβ1 chains encoded by HLA-DRB1 alleles: QKRAA, QRRAA and RRRAA. The present study aims to analyze whether SE-peptides (SE-p) can be a target of the autoimmune response in RA. Objectives: To analyze the presence of AAb against the unmodified ( Un ) SE-p, citrullinated ( Cit ) SE-p and carbamylated ( Car ) SE-p. Methods: Sera from consecutive 117 RA patients and 21 psoriasic arthritis (PsA) from our outpatient clinic were collected by venopunture. Also 138 sera from blood donors were obtained as healthy controls (HC). All participants signed the informed consent. We perfomed a homemade ELISA test using a sequence of 15 aminoacid peptides from positions 65-79 of HLA-DRB1 containing the 3 different SE sequences, in the Un , Cit and Ca r SE-p, synthesized in a linear and cycled form. We established a 90% of specificity using a ROC curve obtained from HC and PsA for each ELISA test. HLA-DRB1 polymorphism was performed using a HLA-DRB1 sequence specific oligonucleotide typing kit (Lifecodes) in 95 RA and in 15 PsA. ACPA and RF were determined with commercial assays (Inova Diagnostics and Binding Site, respectively). Results: The overall sensitivity of the different SE-p AAb tests ranged from 5.1-21.4%. RRRAA SE polymorphism was associated with AAb against cycled CitCitCitAA SE-p (p=0.025), QKRAA polymorphism was almost significantly associated with AAb against cycled QKCitAA SE-p (p=0.067), whereas there was no association between QRRAA polymorphism and AAb against cycled QCitCitAA SE-p (p=0.690). On the other hand, there was no association between SE polymorphisms and AAb to any other peptide used in the ELISA test. Significant differences were observed in the presence of AAb against lineal RRRAA, lineal CitCitCitAA and cycled CitCitCitAA SE-p when comparing RA vs. HC patients (p=0.022, 0.044, 0.022, respectively). Moreover, there also were significant differences in the presence of AAb against cycled CitCitCitAA SE-p between RA and PsA patients (sensitivity 21.4%, specificity 100%; p=0.014). It must be highlighted that cycled CitCitCitAA SE-p AAb were detected in 20.0% of RA patient sera that were negative for RF and ACPA. There was no association between RF or ACPA with the presence of any SE-p AAb. Conclusion: RA patients have autoantibodies against the Shared Epitope (SE). The cycled CitCitCitAA SE peptide (SE-p) shows the best performance among all the peptides tested and could identify patients seronegative for ACPA and RF, both analyzed by commercial assays. Additional studies must be performed to verify the diagnostic and utility of these new autoantibodies against SE-p in RA. Acknowledgements: This work was granted by the 2018 call of the “Fundación Española de Reumatologia” and the 2017 call grant “Fundació Parc Taulí”. Disclosure of Interests: None declared