title: CXCL12γ isoform is expressed on endothelial and dendritic cells in rheumatoid arthritis synovium and regulates T cell activation.
abstract: OBJECTIVE
  CXCL12γ is an alternative splicing isoform of CXCL12 with enhanced affinity for heparan sulfate (HS) proteoglycans. This study was undertaken to investigate the distribution and potential function of CXCL12γ in rheumatoid arthritis (RA) synovium and normal lymphoid tissue, where its immobilization to HS may be relevant in pathologic or homeostatic immune cell migration and activation.
  
  
  METHODS
  Expression of CXCL12 or CXCL12γ was immunodetected in RA and normal synovium, lymphoid tissue, and cultured cells with anti-pan-CXCL12 or anti-CXCL12γ-specific monoclonal antibodies. CXCL12α and CXCL12γ messenger RNA expression was analyzed by quantitative reverse transcription-polymerase chain reaction. Binding of wild-type CXCL12 isoforms or their HS binding-defective mutants to monocyte-derived dendritic cells (DCs) was analyzed by flow cytometry. The effect of DC-bound CXCL12α and CXCL12γ on T cell activation was analyzed in DC/T cell allogeneic cultures.
  
  
  RESULTS
  CXCL12γ expression was increased in RA compared to normal synovium and preferentially located in endothelia and DC-SIGN-positive cells. This distribution was also observed in lymphoid organs. Surface-bound CXCL12γ was detected in a fraction of freshly isolated DCs. Monocyte-derived DCs, but not monocytes, showed a high capacity to bind CXCL12γ in an HS-dependent manner. Surface-bound CXCL12α and CXCL12γ on monocyte-derived DCs were potent inhibitors of allogeneic T cell activation, in contrast to the T cell-stimulatory effects of soluble CXCL12 proteins.
  
  
  CONCLUSIONS
  CXCL12γ shows a specific and similar distribution in RA synovium and lymphoid tissue, consistent with its higher HS binding affinity. Presentation of CXCL12 to T cells on membrane HS in DCs can play a distinct regulatory role in T cell activation.
authors.affiliation: Hospital 12 de Octubre and Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Begoña
authors.initials: B
authors.lastname: Santiago
authors.forename: Elena
authors.initials: E
authors.lastname: Izquierdo
authors.forename: Patricia
authors.initials: P
authors.lastname: Rueda
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Del Rey
authors.forename: Gabriel
authors.initials: G
authors.lastname: Criado
authors.forename: Alicia
authors.initials: A
authors.lastname: Usategui
authors.forename: Fernando
authors.initials: F
authors.lastname: Arenzana-Seisdedos
authors.forename: José L
authors.initials: JL
authors.lastname: Pablos
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000235:genetics / Q000378:metabolism*; D003713:Dendritic Cells / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008213:Lymphocyte Activation / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D013583:Synovial Membrane / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism*
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019812:Heparan Sulfate Proteoglycans; D020033:Protein Isoforms