Transmembrane BAFF from rheumatoid synoviocytes requires interleukin-6 to induce the expression of recombination-activating gene in B lymphocytes.
OBJECTIVE
B cells that accumulate in the synovial tissue of rheumatoid arthritis (RA) patients revise their receptors due to coordinate expression of recombination-activating gene 1 (RAG-1) and RAG-2 genes. The aim of this study was to determine the mechanisms that control this re-expression.


METHODS
B cells from healthy control subjects were cocultured with fibroblast-like synoviocytes (FLS) from patients with RA and osteoarthritis (OA). Re-expression of RAG messenger RNA (mRNA) and proteins was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and indirect immunofluorescence. Activity of RAG enzymes was evaluated by flow cytometry to measure variations in immunoglobulin kappa and lambda light chain expression and by ligation-mediated-PCR to assess specific DNA breaks. Blocking antibodies, short hairpin RNA, and recombinant cytokine were used to identify the molecules involved in RAG re-expression.


RESULTS
RA FLS, but not OA FLS, induced B cells to re-express RAG mRNA and proteins. Enzymes were functional, since the kappa-to-lambda ratios decreased and specific DNA breaks were detectable after coculture with RA FLS. Transmembrane BAFF provided the first signal of RAG re-expression, since its down-regulation in RA FLS prevented RAG gene transcription in B cells. The failure of transmembrane BAFF from OA FLS to induce RAG suggests that a second signal was provided by RA FLS. Interleukin-6 (IL-6) is a candidate, since blockade of its receptors precluded transcription of RAG genes by RA FLS. Unless supplemented with IL-6, OA FLS were unable to induce RAG gene expression in normal B cells.


CONCLUSIONS
Two independent signals are required for the induction of RAG gene expression in B cells that infiltrate the synovium of patients with RA.
Rochas
Caroline
C
Université Européenne de Bretagne, Université de Brest, IFR 148 ScInBioS, and Laboratory of Immunology, Centre Hospitalier Universitaire, Brest Hôpital Morvan and Cavale Blanche, Brest, France.
Hillion
Sophie
S
Saraux
Alain
A
Mageed
Rizgar A
RA
Youinou
Pierre
P
Jamin
Christophe
C
Devauchelle
Valérie
V
D001172:Arthritis, Rheumatoid / Q000235:genetics*; D053265:B-Cell Activation Factor Receptor / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics*; D015870:Gene Expression; D015321:Gene Rearrangement; D016654:Genes, RAG-1; D006801:Humans; D015850:Interleukin-6 / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics*; D010003:Osteoarthritis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000166:cytology*; D015854:Up-Regulation
D053265:B-Cell Activation Factor Receptor; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D009687:Nuclear Proteins; C499311:RAG2 protein, human; D012333:RNA, Messenger