title: Phagocytic lining cells determine local expression of inflammation in type II collagen-induced arthritis.
abstract: OBJECTIVE
  To investigate the in vivo role of phagocytic synovial lining cells in the local expression of inflammation in type II collagen-induced arthritis (CIA) in DBA/1J mice.
  
  
  METHODS
  On various days before arthritis induction (day 7, 5, or 2), phagocytic lining cells were selectively depleted from the synovial layer by injecting multilamellar liposomes containing clodronate (dichloromethylene diphosphonate) directly into the knee joints. As controls, either PBS or PBS-laden liposomes were injected. CIA was induced by immunizing mice with heterologous bovine type II collagen in Freund's complete adjuvant. Arthritis onset was synchronized by a single intraperitoneal injection of lipopolysaccharide; arthritis was evaluated in hematoxylin and eosinstained knee joint sections. Chemotactic activity in synovial washout samples was detected in a Transwell chemotactic assay. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) protein levels were measured in NOB-1 and L929 bioassays, respectively. IL-1 messenger RNA (mRNA) in synovial specimens was measured by reverse transcriptase-polymerase chain reaction. IL-1 was also detected immunohistologically in knee joint sections.
  
  
  RESULTS
  In clodronate-laden liposome-treated, lining-depleted knee joints, there was significantly decreased inflammation compared with controls. Cell influx into the synovium was markedly decreased. Expression of IL-1 mRNA in the synovium was significantly reduced. IL-1 was detected only in some cells in the deeper synovial layer, in contrast to controls, in which large numbers of cells in the deeper synovial layer were stained. In synovial washouts from lining-depleted knee joints, biologically active IL-1 levels were reduced by 40% at 6 hours after arthritis induction. Most strikingly, chemotactic activity was highly decreased in these synovial washout samples. When IL-1 or TNF alpha was injected into the knee joints of immunized mice in which arthritis was not yet expressed, arthritis was not induced in the lining-depleted joints, whereas marked cell influx was found in control joints.
  
  
  CONCLUSIONS
  Our data indicate that phagocytic lining cells play a crucial role in the local expression of inflammation in systemically induced CIA. Phagocytic lining cells probably form an important source of chemotactic factors which are set free upon activation by IL-1 or TNF alpha.
authors.affiliation: Department of Rheumatology, University Hospital Nijmegen, The Netherlands.
authors.forename: P L
authors.initials: PL
authors.lastname: van Lent
authors.forename: A E
authors.initials: AE
authors.lastname: Holthuysen
authors.forename: L A
authors.initials: LA
authors.lastname: van den Bersselaar
authors.forename: N
authors.initials: N
authors.lastname: van Rooijen
authors.forename: L A
authors.initials: LA
authors.lastname: Joosten
authors.forename: F A
authors.initials: FA
authors.lastname: van de Loo
authors.forename: L B
authors.initials: LB
authors.lastname: van de Putte
authors.forename: W B
authors.initials: WB
authors.lastname: van den Berg
mesh_terms: D000818:Animals; D001168:Arthritis / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D002633:Chemotaxis / Q000502:physiology*; D003094:Collagen; D007375:Interleukin-1 / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D010586:Phagocytes / Q000502:physiology*; D013583:Synovial Membrane / Q000187:drug effects / Q000473:pathology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D007375:Interleukin-1; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D003094:Collagen