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FRI0398 Derailed b cell homeostasis in patients with mixed connective tissue disease
  1. A. Hajas1,
  2. S. Barath1,
  3. P. Szodoray2,
  4. B. Nakken2,
  5. P. Gogolak3,
  6. Z. Szekanecz4,
  7. E. Bodolay1
  1. 1Institute of Medicine, University of Debrecen, Debrecen, Hungary
  2. 2Institute of Immunology, Rikshospitalet, Oslo, Norway
  3. 3Department of Immunology
  4. 4Department of Rheumatology, University of Debrecen, Debrecen, Hungary

Abstract

Background Mixed connective tissue disease (MCTD) is a systemic autoimmune disorder, characterized by the presence of antibodies to U1-RNP protein. Although the exact pathogenesis of MCTD is still unknown, B cell abnormalities characterized by autoantibody formation and polyclonal B cell activation play an important role.

Objectives The aim of the present study was to assess the peripheral B cell subsets in MCTD in the active and inactive stage of the disease, compared with healthy individuals. In order to evaluate the clinical relevance of these findings, the frequencies of B cell subsets were correlated with disease activity and autoantibody levels.

Methods Freshly drawn peripheral blood samples were obtained from 46 MCTD patients, and 20 age- and sex-matched healthy controls. Using anti-CD19, anti-CD27, anti-IgD and anti-CD38 monoclonal antibodies, the following B cell subsets were identified by flow cytometry: 1.transitional B cells (CD19+CD27-IgD+CD38high); 2.naive B cells (CD19+CD27-IgD+CD38low); 3.non-switched memory B cells (CD19+CD27+IgD+); 4.switched memory B cells (CD19+CD27+IgD-); 5.double negative (DN) memory B cells (CD19+CD27-IgD-) and 6.plasma cells (CD19+CD27highIgD-). Disease activity of MCTD was assessed by SLAM score.

Results The proportion of transitional B cells, naive B cells and DN B lymphocytes was higher in MCTD than in controls. Active, untreated MCTD patients had both elevated percentages and absolute numbers of CD19+CD27-IgD+CD38high transitional B cells, compared to the inactive stage (%: p<0.009; absolute number: p< 0.045). Both the relative and absolute number of naive B cells (CD19+CD27-IgD+CD38low) was higher in the active disease, than in the inactive stage (%: p< 0.002; absolute number: p<0.001). The distribution of CD27high plasma cells was significantly higher in patients with MCTD compared to healthy controls (p<0.001), while in the active stage, the proportion of CD27high plasma cells further increased (p<0.001). Positive correlation was found between the number of plasma cells and anti-U1RNP levels. The DN B cells were positive for CD95 surface marker. This memory B cells population showed a close correlation with disease activity (p<0.001).

Conclusions Several abnormalities were found in the peripheral B cell subsets in MCTD, which reinforces the role of derailed humoral autoimmune processes in the pathogenesis of MCTD.

Disclosure of Interest: None Declared

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