title: Quantification of circulating endothelial progenitor cells in systemic sclerosis: a direct comparison of protocols.
abstract: BACKGROUND
  It has been proposed that dysfunctional endothelial progenitor cells (EPCs) play a role in pathogenic vasculopathy in systemic sclerosis (SSc). However, there is some debate as to whether the EPC count is reduced in SSc. The European League Against Rheumatism Scleroderma Trials and Research (EUSTAR) group recently proposed recommendations for evaluating EPCs.
  
  
  OBJECTIVE
  To validate the proposed EUSTAR recommendations by a side-by-side comparison of methods for quantifying EPCs.
  
  
  METHODS
  Peripheral blood samples were obtained from 11 patients with SSc and 11 age-matched healthy controls. EPCs were simultaneously quantified by two methods: flow cytometry combined with immunomagnetic CD34+ cell enrichment or rosette-based lineage-negative (Lin-) cell enrichment. EPCs, defined as CD34+CD133+VEGFR2+ cells, were counted with and without fluorosphere calibration.
  
  
  RESULTS
  EPC counts measured with fluorosphere calibration correlated well with each other, regardless of the enrichment procedure used. In contrast, EPC counts from protocols that did not use fluorospheres correlated poorly with results from other protocols.
  
  
  CONCLUSIONS
  The EUSTAR recommendations are valid when they are combined with fluorosphere calibration.
authors.affiliation: Division of Rheumatology, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan. kuwanam@z5.keio.jp
authors.forename: Masataka
authors.initials: M
authors.lastname: Kuwana
authors.forename: Yuka
authors.initials: Y
authors.lastname: Okazaki
mesh_terms: D000328:Adult; D000368:Aged; D001800:Blood Specimen Collection / Q000379:methods; D016022:Case-Control Studies; D002452:Cell Count; D002469:Cell Separation / Q000379:methods* / Q000592:standards; D042783:Endothelial Cells / Q000473:pathology*; D004730:Endothelium, Vascular / Q000473:pathology*; D005260:Female; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D018189:Immunomagnetic Separation / Q000379:methods; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D015203:Reproducibility of Results; D012397:Rosette Formation; D012595:Scleroderma, Systemic / Q000097:blood*; D013234:Stem Cells / Q000473:pathology*