Detection and isolation of antigen reactive B cells in patients with rheumatoid arthritis
Jenny Nilsson1, Louise Sjökvist Ottsjö1, Karin Önnheim1, Maria Bergquist1, Inga-Lill Mårtensson1, Johan Viljanen2, Erik Lönnblom3, Outi Sareila3, Bingze Xu3, Jan Kihlberg2, Rikard Holmdahl3, Inger Gjertsson1
1Dept of Rheumatology and Inflammation Research, Göteborg University; 2Department of Chemistry, BMC, Uppsala University; 3Medical Inflammation Research, Dept of medical Biochemistry and biophysics, Karolinska Institutet
The majority of autoimmune diseases, e.g. rheumatoid arthritis (RA), are characterized by autoantibodies produced by B cells. We have identified several novel post-translationally modified autoreactive epitopes in collagen type II (CII), a major cartilage constituent. The aim of this project is to study the B cells that produce autoantibodies reactive to CII-epitopes in peripheral blood in RA patients (n=15). The different subsets of B cells that expressed a CII-reactive B cell receptor (BCR) were analysed and isolated in patients with positive (n=10) or negative (n=5) titres for serum autoantibodies recognizing the CII-epitopes cyc48 (CII-F4-R-Cit) and cyc49 (CII-F4-Cit-R) as well as in healthy controls (n=3) using flow cytometry. Patients with detectable serum autoantibodies to cyc48 and cyc49 had titres of 13761±3815 and 5585±1992 (mean ± SEM), respectively. The corresponding titres in autoantibody-negative patients were 122±55 and 234±75. In autoantibody-positive patients, the frequencies of cells expressing a BCR reactive for cyc48 and cyc49 in different subsets were: transitional cells 0.88±0.18 % and 1.33±0.33 %; naïve cells 0.09±0.0008% and 0.13±0.06 and memory cells 0.31±0.25 and 0.30±0.12%, and were increased compared to patients without cyc48/49 titres and healthy controls. In conclusion, in patients with manifested RA there is a relatively high frequency of transitional B cells that express a joint-specific BCR, which suggests that the deletion of autoreactive B cells in the bone marrow in RA patients is defective. However, peripheral B-cell tolerance is incomplete, as CII-specific B cells are enriched in the pool of memory B cells.