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AB0039 The Frequency of Acpa-Specific B Cells in the Circulating Memory B Cell Pool of Patients with Rheumatoid Arthritis
  1. U. Saunders,
  2. T. Fassbinder,
  3. H. Becker,
  4. E. Jung,
  5. E. Mickholz,
  6. A.M. Jacobi
  1. Division of Rheumatology and Clinical Immunology/Internal Medicine D, University Hospital Münster, Münster, Germany

Abstract

Background Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterized by the presence of autoantibodies (AA) such as rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPAs). These AA do not only play a pivotal role in diagnostics, but also in pathogenesis of RA. AA can be secreted by long-lived plasma cells homing to the bone marrow or by newly generated plasma cells derived from the memory B cell pool.

Objectives To determine the frequency of ACPA-specific cells within the circulating memory B cell pool of ACPA-positive RA patients.

Methods In order to compare the frequency of anti-cyclic citrullinated peptid (CCP) and anti-mutated citrullinated vimentin (MCV) antibody specific B cells within the memory B cell pool of 7 CCP- and 7 MCV-positive patients with RA and 4 or 6 normal healthy subjects (NHS) we analyzed antibody secretion by ELISPOT after transforming memory B cells into plasmablasts (PB). For comparison we determined the frequency of tetanus toxoid (TT)-specific B cells in the circulating pool of memory B cells of 8 TT-vaccinated NHS. CD27+ memory B cells were isolated from peripheral blood samples. After polyclonal activation for 4 days the percentage of PB (CD27++) was determined by flow cytometry. To determine the frequency of anti-CCP, anti-MCV and anti-TT antibody secreting cells ELISPOT assays (IgM, IgG, IgA) were performed.

Results Flow cytometric analysis revealed that after 4 days 62±11% (RA n=14) and 62±13% (NHS n=18) of all viable cells in culture adopted the phenotype of CD27++ PB. The frequencies of antigen-specific B cells of all individuals are shown in Table 1. In contrast to NHS, 71.4% of CCP-positive and 28.6% of all MCV-positive RA patients had detectable frequencies of CCP- or MCV-specific IgG antibody secreting cells (ASC). In these individuals the frequencies of ACPA-secreting cells were lower than the frequency of anti-TT-specific IgG ASC in TT-vaccinated NHS, who all had detectable frequencies of TT-specific IgG ASC (CCP: 0.22±0.21%, MCV: 0.34±0.40, TT: 0.9±0.7).

Table 1.

Frequency of antigen-specific spots in relation to total IgM, IgG and IgA spots

Conclusions Using this approach, ACPA-specific B cells can be detected in the circulating memory B cell pool only in a subset of ACPA-positive RA patients. In the remaining patients, ACPA-specific B or plasma cells might home in the bone marrow or inflamed joints.

Disclosure of Interest U. Saunders Grant/research support: Chugai Pharmaceutical Co., Ltd., T. Fassbinder: None declared, H. Becker: None declared, E. Jung: None declared, E. Mickholz: None declared, A. Jacobi Grant/research support: Chugai Pharmaceutical Co., Ltd.

DOI 10.1136/annrheumdis-2014-eular.2229

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