title: Mast cells are the main interleukin 17-positive cells in anticitrullinated protein antibody-positive and -negative rheumatoid arthritis and osteoarthritis synovium.
abstract: BACKGROUND
  Mast cells have been implicated to play a functional role in arthritis, especially in autoantibody-positive disease. Among the cytokines involved in rheumatoid arthritis (RA), IL-17 is an important inflammatory mediator. Recent data suggest that the synovial mast cell is a main producer of IL-17, although T cells have also been implicated as prominent IL-17 producers as well. We aimed to identify IL-17 expression by mast cells and T cells in synovium of arthritis patients.
  
  
  METHODS
  Synovial samples of anticitrullinated protein antibody-positive (ACPA+) and ACPA-negative (ACPA-) RA and osteoarthritis (OA) patients were stained for IL-17 in combination with CD117 (mast cells), CD3 (T cells) and CD68 (macrophages). Concentrations of IL-17 in synovial fluid were determined by ELISA.
  
  
  RESULTS
  The number of IL-17+ cells in synovium was comparable in all groups. Although the vast majority of IL-17+ cells are mast cells, no difference in the percentage of IL-17+ mast cells was observed. Nonetheless, levels of IL-17 in synovial fluid were increased in ACPA+ RA patients compared to ACPA- RA and OA patients.
  
  
  CONCLUSIONS
  The synovial mast cell is the main IL-17+ cell in all three arthritis groups analyzed. These data are relevant for studies aimed at blocking IL-17 in the treatment of arthritis.
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, PO Box 9600, Albinusdreef 2, C1-R, NL-2300 RC Leiden, The Netherlands. j.suurmond@lumc.nl
authors.forename: Jolien
authors.initials: J
authors.lastname: Suurmond
authors.forename: Annemarie L
authors.initials: AL
authors.lastname: Dorjée
authors.forename: Mariëtte R
authors.initials: MR
authors.lastname: Boon
authors.forename: Edward F
authors.initials: EF
authors.lastname: Knol
authors.forename: Tom W J
authors.initials: TW
authors.lastname: Huizinga
authors.forename: René E M
authors.initials: RE
authors.lastname: Toes
authors.forename: Annemie J M
authors.initials: AJ
authors.lastname: Schuerwegh
mesh_terms: D000974:Antibodies, Antinuclear / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D001323:Autoantibodies / Q000378:metabolism; D006801:Humans; D020381:Interleukin-17 / Q000096:biosynthesis*; D008407:Mast Cells / Q000378:metabolism* / Q000473:pathology; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology
chemical_list: D000974:Antibodies, Antinuclear; D001323:Autoantibodies; D020381:Interleukin-17