Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Expression of the Idiotope 9G4 on Autoantibodies and B Cells from Patients with Rheumatoid Arthritis (RA): Description of a New B Cell Phenotype.

Torre1,  Inmaculada De la, Moura2,  Rita, Leandro3,  Maria J., Edwards3,  Jonathan C. W., Cambridge3,  Geraldine

Hospital Gregorio Maranon, Madrid, Spain
Instituto de Biologia Molecular, Lisbon, Portugal
University College London, London, UK

Background:

The rat monoclonal antibody 9G4 recognises an idiotope on V4–34-derived immunoglobulins(Ig). Antibodies encoded by V4–34 region are inherently autoreactive against red blood cell determinants. An estimated 15% of naïve B cells are 9G4+ but <1% of circulating Ig are 9G4+ in healthy controls (HC). In HC, 9G4+ B cells of a mature pre-switch phenotype (IgM+IgD+CD27+) are found in splenic marginal zones (MZ). 9G4+ B cells are also in tonsils from HC but excluded from germinal center (GC) reactions. Whereas in patients with lupus, post-GC memory B cells (IgD-CD27+) are present, suggesting defective B cell censoring (1). In RA, there is also some evidence that B cell tolerance is affected.

Objective:

To determine whether RhF from RA and disease controls express 9G4 and to examine the phenotype of 9G4+ B cells in peripheral blood.

Methods:

9G4-expression on RhF and on total serum IgM and IgG were measured by ELISA in 22 seropositive RA and 20 RhF+ve 1o Sjogrens Syndrome (SS). Peripheral blood CD19+ B cells from 24 patients with RA and 7 HC were obtained by negative selection using MACs columns and stained to distinguish 9G4 expression on CD5 and CD27 populations and also within naïve (IgD+CD38+), transitional (IgD+CD38++), memory post-GC (IgD-CD38+), memory resting (IgD-CD38) and plasmablast (IgD-CD38+++) populations. Analyses were by Mann Whitney rank sum test.

Results:

RhF levels and expression of 9G4 on total IgM and IgG were minimally higher in RA than SS patients (p<0.05). However 9G4 expression on RhF was significantly greater (p<0.0001) in RA vs SS patients. Percentages of 9G4+CD19+ B cells in HC and RA patients were similar (mean %: 6.36 vs 6.45) and most had a naïve phenotype (means: 44%, 42% respectively). Post-GC B cells and plasmablasts had means of 14.5% and 3.5% for NC and, for RA, 29.5% and 9.2% respectively. Gating on the 9G4+ population, CD5-CD27- phenotype was the most common in NC and RA (58.7% vs 55.7%). However a distinct population was described with a CD5+CD27+ B cell phenotype with similar proportions in HC and RA (13.1% vs 17.4%). Further, in some RA patients, a negative correlation was found between the percentage of B cells expressing CD5+CD27+ and 9G4 expression on RhF in the same sample.

Conclusions:

Although post-GC 9G4+ B cells were not found in RA tonsils, we found 9G4 on RhF in patients with RA but not in SS. As RhF from patients with SS do not utilize V4–34, this suggests breakdown of 9G4 censoring in patients with RA, perhaps in areas outside secondary lymphoid tissue such as in the spleen or inflamed joints. We also found that HC and RA patients had circulating 9G4+ memory B cells and plasmablasts and describe a new B cell phenotype, CD19+CD5+CD27+, which often carries the 9G4 idiotope. CD5 is found on B cells in splenic MZ and is lost from B cells before entry into late stages of a GC. Also, CD27+ B cells have been shown to be predominantly CD5-CD23-. We suggest that retention of CD5 expression on 9G4+CD27+ B cells, whilst allowing development of a mature phenotype may be a self-censoring mechanism preventing access to GCs (perhaps by affecting BCR signaling) and hence antibody production from these potentially 'dangerous' autoreactive cells.

To cite this abstract, please use the following information:
Torre, Inmaculada De la, Moura, Rita, Leandro, Maria J., Edwards, Jonathan C. W., Cambridge, Geraldine; Expression of the Idiotope 9G4 on Autoantibodies and B Cells from Patients with Rheumatoid Arthritis (RA): Description of a New B Cell Phenotype. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :743
DOI: 10.1002/art.28511

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