title: Mature antigen-experienced T helper cells synthesize and secrete the B cell chemoattractant CXCL13 in the inflammatory environment of the rheumatoid joint.
abstract: OBJECTIVE
  Synovial B cells play a critical role in rheumatoid arthritis (RA), being involved in autoantibody synthesis, T cell activation, and cytokine production. CXCL13 is a B cell chemoattractant that is instrumental in synovial B cell organization; the regulatory determinants of CXCL13 in inflammation are poorly characterized. This study was undertaken to investigate the functional involvement of synovial T cells in the ectopic expression of CXCL13 in RA.
  
  
  METHODS
  CXCL13 production and regulation were addressed using immunohistochemistry, in situ hybridization, quantitative polymerase chain reaction, multicolor flow cytometry, and enzyme-linked immunosorbent assay, by in situ-ex vivo analysis and in vitro functional assays with rheumatoid synovial tissue and primary cells.
  
  
  RESULTS
  CXCL13 messenger RNA and protein expression and spontaneous CXCL13 secretion were detected in RA synovial fluid T cells but were not detected (or were detected only occasionally) in peripheral blood T cells. Analysis of tissue expression confirmed cytoplasm localization of CXCL13 in T lymphocytes infiltrating B cell follicles and small perivascular aggregates. Multicolor characterizations in synovial fluid demonstrated CXCL13 expression in antigen-experienced T helper cells, frequently characterized by terminal differentiation and the lack of the follicular helper T cell markers CXCR5 and BCL6 protein. In vitro functional assays revealed the enhancing effect of T cell receptor-CD28 engagement on CXCL13 production and secretion in primary cells.
  
  
  CONCLUSIONS
  Our findings define a new functional property of synovial T cells, demonstrating their active involvement in the local production of B cell chemoattractants, and support a direct contribution of the adaptive immune system and antigen-dependent signals in the mechanisms of B cell localization in RA.
authors.affiliation: St. Bartholomew's and Royal London School of Medicine, London, UK.
authors.forename: Antonio
authors.initials: A
authors.lastname: Manzo
authors.forename: Barbara
authors.initials: B
authors.lastname: Vitolo
authors.forename: Frances
authors.initials: F
authors.lastname: Humby
authors.forename: Roberto
authors.initials: R
authors.lastname: Caporali
authors.forename: David
authors.initials: D
authors.lastname: Jarrossay
authors.forename: Francesco
authors.initials: F
authors.lastname: Dell'accio
authors.forename: Laura
authors.initials: L
authors.lastname: Ciardelli
authors.forename: Mariagrazia
authors.initials: M
authors.lastname: Uguccioni
authors.forename: Carlomaurizio
authors.initials: C
authors.lastname: Montecucco
authors.forename: Costantino
authors.initials: C
authors.lastname: Pitzalis
mesh_terms: D000328:Adult; D000368:Aged; D000941:Antigens / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology; D054382:Chemokine CXCL13 / Q000096:biosynthesis* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000032:analysis; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D051560:Proto-Oncogene Proteins c-bcl-6; D012333:RNA, Messenger / Q000032:analysis; D054380:Receptors, CXCR5 / Q000032:analysis; D013582:Synovial Fluid / Q000737:chemistry; D013583:Synovial Membrane / Q000166:cytology / Q000276:immunology; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
chemical_list: D000941:Antigens; C084103:BCL6 protein, human; C095085:CXCR5 protein, human; D054382:Chemokine CXCL13; D004268:DNA-Binding Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D012333:RNA, Messenger; D054380:Receptors, CXCR5