title: Effect of age on plasma membrane asymmetry and membrane fluidity in human leukocytes and platelets.
abstract: BACKGROUND
  We determined whether ageing changes in plasma membrane phospholipid asymmetry were related to changes in membrane physical characteristics.
  
  
  METHODS
  Plasma membrane asymmetry was determined in polymorphonuclear leukocytes (PMN), lymphocytes, and platelets from 45 healthy young (mean 29 years, 26 male) and 28 healthy elderly (mean 70 years, 15 male) subjects by flow cytometric measurement of annexin V binding to cell surface phosphatidylserine. Membrane fluidity in lymphocytes and platelets from young and elderly subjects was determined by fluorescence polarization of 1,6-diphenyl- 1,3,5-hexatriene (DPH) and (4-trimethylammonium)-DPH (TMA).
  
  
  RESULTS
  In elderly subjects, a higher proportion of lymphocytes had specific annexin V binding to phosphatidylserine (PS) than in young subjects (young: median percentage of cells with specific annexin V binding to PS 5.3 [second to fourth quintiles range 3.8-8.7]; elderly: 8.5 [5.2-17.2]; p = .028). No ageing change in annexin V binding to PMN was observed (young: 35.0% [21.8-53.5]; elderly: 39.6% [27.4-69.8]; p = .42). Platelets had no specific annexin V binding (young: median molecules of annexin V specific binding 3.8 [0.4-11.3]; elderly: -1.4 [-4.8-1.7]; p = .23). Superficial membrane fluidity was increased in lymphocytes (TMA anisotropy, young: 0.271 [0.259-0.289]; elderly: 0.262 [0.242-0.279];p = .004), but not in platelets (young: 0.273 [0.259-0.293]; elderly: 0.269 [0.248-0.284]; p = .12). Lymphocyte annexin V binding correlated with TMA (r = -.65, p = .022), but not DPH anisotropy (r = -.39, p = .18).
  
  
  CONCLUSIONS
  Plasma membrane asymmetry is decreased with age in human lymphocytes, but not in human PMN or platelets. The increased proportion of lymphocytes with loss of plasma membrane asymmetry corresponds to the ageing changes in superficial membrane fluidity observed in lymphocytes. Such alterations in lymphocyte plasma membrane structure with age could account for changes in membrane-bound receptor function described with ageing, and may contribute to alterations in immune responsiveness and vascular thrombosis seen in older humans.
authors.affiliation: Department of Medicine, University of Newcastle Upon Tyne, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Noble
authors.forename: T H
authors.initials: TH
authors.lastname: Thomas
authors.forename: G A
authors.initials: GA
authors.lastname: Ford
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D017304:Annexin A5 / Q000378:metabolism; D001792:Blood Platelets / Q000502:physiology / Q000648:ultrastructure*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D004161:Diphenylhexatriene / Q000031:analogs & derivatives; D005434:Flow Cytometry; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D006801:Humans; D008214:Lymphocytes / Q000502:physiology / Q000648:ultrastructure*; D008297:Male; D008560:Membrane Fluidity / Q000502:physiology*; D008563:Membrane Lipids / Q000502:physiology; D009504:Neutrophils / Q000502:physiology / Q000648:ultrastructure*; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000502:physiology; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000502:physiology / Q000648:ultrastructure; D012044:Regression Analysis
chemical_list: D017304:Annexin A5; D005456:Fluorescent Dyes; D008563:Membrane Lipids; D010718:Phosphatidylserines; D010743:Phospholipids; D011956:Receptors, Cell Surface; D004161:Diphenylhexatriene; C033628:1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene