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B cells and autoantibodies: diagnosis and pathophysiology
Oral presentation
TRANSMEMBRANE BAFF FROM RHEUMATOID SYNOVIOCYTES, COUPLED WITH IL-6, INDUCES THE EXPRESSION OF RECOMBINATION-ACTIVATING GENE (RAG) IN NORMAL B CELLS
C. Rochas, C. Jamin, S. Hillion, A. Saraux, P. Youinou, V. Devauchelle. Brest University Medical School Hospital, Brest, France
Background: Rheumatoid arthritis (RA) is the most frequent chronic inflammatory disorder leading to major changes in synovial tissue (ST) with fibroblast like synoviocyte (FLS) activation and hyperplasia, and major inflammatory infiltration. Lymphoid cells in the ST may be diffuse or arranged in germinal centres (GCs). The V(D)J gene combinations are revised in the germinal centres by the recombination-activating gene (RAG) 1 and RAG2 enzymes, provided their B cell expression is coordinate. The present work was designed to gain insight into the mechanisms regulating expression of RAGs in B-cells and their functionality in secondary Ig rearrangements in RA.
Methods: We elaborated a model of co-culture of normal peripheral B cells with RA-FLS, to induce RAGs expression. Using single cell PCR and immunofluorescence analysis we evaluated RAGs expression due to RA-FLS contact at the mRNA and protein level. Using an LM-PCR analysis to detect Jκ and/or Jλ gene rearrangements, we explore the ability of RAGs to induce V(D)J rearrangements. We explore the role of IL-6 in this model using ELISA measurement and co-culture with IL-6 antibody and the role of BAFF using BAFF-deficient RA-FLS generated by short hairpin (sh) gene interference mechanism.
Results: We present mRNA and protein evidence that fibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA), but not from osteoarthritis (OA), induce the expression of RAG in normal B cells. This expression is turned off by engagement of the BCR. One feature in the RAG expression is the transmembrane form of BAFF on RA-FLS. Consistent with this, shRNA downregulates the synthesis of BAFF preventing thereby RA-FLS to trigger RAG, and this failure is not reverted by rBAFF. However, the fact that OA-FLS do not induce RAGs, despite their expression of BAFF, suggests …