title: CXCL16-mediated cell recruitment to rheumatoid arthritis synovial tissue and murine lymph nodes is dependent upon the MAPK pathway.
abstract: OBJECTIVE
  Rheumatoid arthritis (RA) is characterized by profound mononuclear cell (MNC) recruitment into synovial tissue (ST), thought to be due in part to tumor necrosis factor alpha (TNFalpha), a therapeutic target for RA. Although chemokines may also be involved, the mechanisms remain unclear. We undertook this study to examine the participation of CXCL16, a novel chemokine, in recruitment of MNCs to RA ST in vivo and to determine the signal transduction pathways mediating this process.
  
  
  METHODS
  Using a human RA ST-SCID mouse chimera, immunohistochemistry, enzyme-linked immunosorbent assay, real-time reverse transcription-polymerase chain reaction, flow cytometry, and in vitro chemotaxis assays, we defined the expression and function of CXCL16 and its receptor, CXCR6, as well as the signal transduction pathways utilized by them for MNC homing in vitro and in vivo.
  
  
  RESULTS
  CXCL16 was markedly elevated in RA synovial fluid (SF) samples, being as high as 145 ng/ml. Intense macrophage and lining cell staining for CXCL16 in RA ST correlated with increased CXCL16 messenger RNA levels in RA ST compared with those in osteoarthritis and normal ST. By fluorescence-activated cell sorting analysis, one-half of RA SF monocytes and one-third of memory lymphocytes expressed CXCR6. In vivo recruitment of human MNCs to RA ST implanted in SCID mice occurred in response to intragraft injection of human CXCL16, a response similar to that induced by TNFalpha. Lipofection of MNCs with antisense oligodeoxynucleotides for ERK-1/2 resulted in a 50% decline in recruitment to engrafted RA ST and a 5-fold decline in recruitment to regional lymph nodes. Interestingly, RA ST fibroblasts did not produce CXCL16 in response to TNFalpha in vitro, suggesting that CXCL16 protein may function in large part independently of TNFalpha.
  
  
  CONCLUSIONS
  Taken together, these results point to a unique role for CXCL16 as a premier MNC recruiter in RA and suggest additional therapeutic possibilities, targeting CXCL16, its receptor, or its signaling pathways.
authors.affiliation: University of Michigan Medical School, Ann Arbor 48109-0680, USA.
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Ruth
authors.forename: Christian S
authors.initials: CS
authors.lastname: Haas
authors.forename: Christy C
authors.initials: CC
authors.lastname: Park
authors.forename: M Asif
authors.initials: MA
authors.lastname: Amin
authors.forename: Rita J
authors.initials: RJ
authors.lastname: Martinez
authors.forename: G Kenneth
authors.initials: GK
authors.lastname: Haines
authors.forename: Shiva
authors.initials: S
authors.lastname: Shahrara
authors.forename: Phillip L
authors.initials: PL
authors.lastname: Campbell
authors.forename: Alisa E
authors.initials: AE
authors.lastname: Koch
mesh_terms: D000818:Animals; D001172:Arthritis, Rheumatoid / Q000473:pathology*; D002464:Cell Migration Inhibition; D000075743:Chemokine CXCL16; D019743:Chemokines, CXC / Q000502:physiology*; D002633:Chemotaxis; D002678:Chimera; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D006822:Hybrid Cells; D007150:Immunohistochemistry; D007963:Leukocytes, Mononuclear / Q000502:physiology*; D008198:Lymph Nodes / Q000473:pathology*; D051379:Mice; D016513:Mice, SCID; D000075744:Receptors, CXCR6; D019707:Receptors, Chemokine; D018121:Receptors, Cytokine / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000502:physiology; D051116:Receptors, Scavenger / Q000502:physiology*; D011991:Receptors, Virus / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013582:Synovial Fluid / Q000737:chemistry; D013583:Synovial Membrane / Q000473:pathology*
chemical_list: C423727:CXCL16 protein, human; C106330:CXCR6 protein, human; D000075743:Chemokine CXCL16; D019743:Chemokines, CXC; D000075744:Receptors, CXCR6; D019707:Receptors, Chemokine; D018121:Receptors, Cytokine; D043562:Receptors, G-Protein-Coupled; D051116:Receptors, Scavenger; D011991:Receptors, Virus