title: Histones induce phosphatidylserine exposure and a procoagulant phenotype in human red blood cells.
abstract: BACKGROUND
  Extracellular histones exert part of their prothrombotic activity through the stimulation of blood cells. Besides platelets, histones can bind to red blood cells (RBCs), which are important contributors to thrombogenesis, but little is known about the functional consequences of this interaction.
  
  
  OBJECTIVE
  To evaluate the effect of histones on the procoagulant potential of human RBCs with particular regard to the expression of surface phosphatidylserine (PS).
  
  
  METHODS
  PS exposure on human RBCs treated with a natural mixture of histones or recombinant individual histones was evaluated with fluorescein isothiocyanate-annexin-V binding and measured with flow cytometry. Calcium influx in RBCs loaded with the calcium-sensitive fluorophore Fluo-4 AM was assessed with flow cytometry. The procoagulant potential of histone-treated RBCs was evaluated with a purified prothrombinase assay and a one-stage plasma recalcification clotting test.
  
  
  RESULTS
  Natural histones induced PS exposure on RBCs in a dose-dependent manner, and neutralization or cleavage of histones by heparin or activated protein C, respectively, abolished PS externalization. H4 was mainly responsible for the stimulating activity of histones, whereas the other subtypes were almost ineffective. Similarly, natural histones and H4 induced influx of calcium into RBCs, whereas the other individual histones did not. Histone-induced exposure of PS on RBCs translated into increased prothrombinase complex-mediated prothrombin activation and accelerated fibrin formation in plasma.
  
  
  CONCLUSIONS
  Histones induce RBCs to express a procoagulant phenotype through the externalization of PS. This finding provides new insights into the prothrombotic activity of extracellular histones.
authors: Coagulation Biology Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.
authors: F
authors: F
authors: Semeraro
authors: C T
authors: CT
authors: Ammollo
authors: N L
authors: NL
authors: Esmon
authors: C T
authors: CT
authors: Esmon
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry; D000818:Animals; D017304:Annexin A5 / Q000737:chemistry; D001777:Blood Coagulation; D001792:Blood Platelets / Q000378:metabolism; D002118:Calcium / Q000737:chemistry; D002417:Cattle; D003029:Coagulants / Q000737:chemistry*; D004912:Erythrocytes / Q000166:cytology*; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D006657:Histones / Q000737:chemistry*; D006801:Humans; D007249:Inflammation; D010641:Phenotype; D010718:Phosphatidylserines / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D013925:Thromboplastin / Q000737:chemistry; D014966:Xanthenes / Q000737:chemistry
chemical_list: D000814:Aniline Compounds; D017304:Annexin A5; D003029:Coagulants; C409648:Fluo 4; D006657:Histones; D010718:Phosphatidylserines; D011994:Recombinant Proteins; D014966:Xanthenes; D013925:Thromboplastin; D016650:Fluorescein-5-isothiocyanate; D002118:Calcium
keywords: blood coagulation; erythrocytes; histones; inflammation; phosphatidylserine