title: Impaired function of endothelial progenitor cells in children with primary systemic vasculitis.
abstract: BACKGROUND
  Previously, we demonstrated that children with active systemic vasculitis (SV) have higher circulating CD34 + CD133 + KDR+ endothelial progenitor cells (EPC); the function of these EPCs, and their relationship with disease activity in vasculitis remains largely unexplored. We hypothesized that although EPC numbers are higher, EPC function is impaired in active SV of the young. The aims of this study were therefore to: 1. investigate the relationship between disease activity and EPC function in children with SV; and 2. study the influence of systemic inflammation on EPC function by investigating the effects of hyperthermia and TNF-α on EPC function.
  
  
  METHODS
  We performed a cross-sectional study of unselected children with SV with different levels of disease activity attending a single center (Great Ormond Street Hospital, London) between October 2008 and December 2014. EPCs were isolated from peripheral blood of children with SV, and healthy child controls. EPC function was assessed by their potential to form colonies (EPC-CFU), and ability to form clusters and incorporate into human umbilical vein endothelial cell (HUVEC) vascular structures in matrigel. The effects of hyperthermia and TNF-α on EPC function were also studied.
  
  
  RESULTS
  Twenty children, median age 12-years (5-16.5; nine males) were studied. EPC-CFU and the number of EPC clusters formed on matrigel were significantly reduced in children with active vasculitis compared with healthy controls (p = 0.02 for EPC-CFU; p = 0.01 for EPC cluster formation). Those with active vasculitis had lower EPC-CFU and EPC cluster formation than those with inactive disease, although non-significantly so. In addition, EPC incorporation into matrigel HUVEC networks was lower in children with SV compared with healthy children, irrespective of disease activity. Ex-vivo pre-treatment of EPC with hyperthermia impaired EPC function; TNF-α down-regulated EPC expression of CD18/CD11b and resulted in decreased incorporation into HUVEC networks.
  
  
  CONCLUSIONS
  Whilst our previous work showed that circulating CD34 + EPC numbers are well preserved, this study revealed that EPC function is significantly impaired in children with vasculitis. It is possible that the chronic inflammatory milieu associated with vasculitis may impair EPC function, and thus contribute to an unfavourable balance between endothelial injury and repair. The mechanism of this remains to be established, however.
authors.affiliation: Infection, Immunity, Immunology and Physiological Medicine, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. y.hong@ucl.ac.uk.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hong
authors.affiliation: Infection, Immunity, Immunology and Physiological Medicine, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. d.eleftheriou@ucl.ac.uk.
authors.forename: Despina
authors.initials: D
authors.lastname: Eleftheriou
authors.affiliation: Infection, Immunity, Immunology and Physiological Medicine, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. n.klein@ucl.ac.uk.
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Klein
authors.affiliation: Infection, Immunity, Immunology and Physiological Medicine, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. p.brogan@ucl.ac.uk.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Brogan
mesh_terms: D000293:Adolescent; D000328:Adult; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D018920:Coculture Techniques; D003094:Collagen; D003114:Colony-Forming Units Assay; D003430:Cross-Sectional Studies; D004338:Drug Combinations; D066026:Endothelial Progenitor Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005260:Female; D061307:Human Umbilical Vein Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007797:Laminin; D008297:Male; D018919:Neovascularization, Physiologic / Q000187:drug effects / Q000502:physiology*; D011509:Proteoglycans; D056647:Systemic Vasculitis / Q000097:blood / Q000503:physiopathology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D055815:Young Adult
chemical_list: D004338:Drug Combinations; D007797:Laminin; D011509:Proteoglycans; D014409:Tumor Necrosis Factor-alpha; C059485:matrigel; D003094:Collagen