title: Characterization of synovial mast cells in knee osteoarthritis: association with clinical parameters.
abstract: OBJECTIVE
  To investigate the presence of mast cells in the osteoarthritic (OA) synovium and their association with clinical parameters in comparison with rheumatoid arthritis (RA) samples.
  
  
  METHODS
  Synovial tissues of 56 symptomatic OA and 49 RA patients were obtained. Two to three paraffin slides were used to quantify inflammation using haematoxylin and eosin (H&E) staining (synovitis score 0-9), and numbers of mast cells (per 10 high-power fields) using double immunofluorescence for CD117 and tryptase. Average scores per patient were used for analysis. Knee radiographs of OA patients were scored according to the Kellgren and Lawrence (KL) system and pain was determined in OA patients at baseline by visual analogue scale (VAS).
  
  
  RESULTS
  Median (range) of mast cells was significantly higher in OA samples 45 (1-168) compared to RA samples 4 (1-47) (P-value < 0.001), despite a lower median (range) synovitis score in OA (2.5 (0-6.0)) compared to 4.6 (0-8.0) in RA samples. The synovitis score was significantly correlated with the number of mast cells (in OA Spearman's rho (P-value) 0.3 (0.023) and RA 0.5 (P-value < 0.001)). Interestingly, we observed a trend towards an association between the number of mast cells and an increased KL-grade (P-value 0.05) in OA patients, independently of synovitis. No associations were found with self-reported pain.
  
  
  CONCLUSIONS
  Prevalence of mast cells in OA synovial tissue is relatively high and associates with structural damage in OA patients, suggesting a role of mast cells in this disease.
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: B.J.E.de_Lange@lumc.nl.
authors.forename: B J E
authors.initials: BJ
authors.lastname: de Lange-Brokaar
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands; Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: G.Kloppenburg@lumc.nl.
authors.forename: M
authors.initials: M
authors.lastname: Kloppenburg
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: Stefan.Andersen@crl.com.
authors.forename: S N
authors.initials: SN
authors.lastname: Andersen
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: A.L.Dorjee@lumc.nl.
authors.forename: A L
authors.initials: AL
authors.lastname: Dorjée
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: angga.yusuf@gmail.com.
authors.forename: E
authors.initials: E
authors.lastname: Yusuf
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: L.van_Toorn@lumc.nl.
authors.forename: L
authors.initials: L
authors.lastname: Herb-van Toorn
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: H.M.J.A.Kroon@lumc.nl.
authors.forename: H M
authors.initials: HM
authors.lastname: Kroon
authors.affiliation: TNO, Leiden, The Netherlands. Electronic address: annemariezuurmond@gmail.com.
authors.forename: A-M
authors.initials: AM
authors.lastname: Zuurmond
authors.affiliation: Janssen Research & Development, LLC, Spring House, PA, USA. Electronic address: VStojano@its.jnj.com.
authors.forename: V
authors.initials: V
authors.lastname: Stojanovic-Susulic
authors.affiliation: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: J.L.Bloem@lumc.nl.
authors.forename: J L
authors.initials: JL
authors.lastname: Bloem
authors.affiliation: Department Orthopaedics, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: R.G.H.H.Nelissen@lumc.nl.
authors.forename: R G H H
authors.initials: RG
authors.lastname: Nelissen
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: R.E.M.Toes@lumc.nl.
authors.forename: R E M
authors.initials: RE
authors.lastname: Toes
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: a.ioan@lumc.nl.
authors.forename: A
authors.initials: A
authors.lastname: Ioan-Facsinay
mesh_terms: D000368:Aged; D001172:Arthritis, Rheumatoid / Q000473:pathology; D001706:Biopsy; D002452:Cell Count; D015550:Cell Degranulation; D005260:Female; D006801:Humans; D008297:Male; D008407:Mast Cells / Q000473:pathology*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D010146:Pain / Q000209:etiology / Q000473:pathology; D011859:Radiography / Q000379:methods; D012720:Severity of Illness Index; D013583:Synovial Membrane / Q000473:pathology*; D013585:Synovitis / Q000473:pathology
keywords: Inflammation; Mast cells; Osteoarthritis (OA)