title: Expression of tissue factor and initiation of clotting by human platelets and monocytes after incubation with porcine endothelial cells.
abstract: OBJECTIVE
  Intravascular thrombosis remains a major barrier to successful pig-to-primate xenotransplantation. However, the precise factors initiating thrombosis are unknown. In this study, we investigated the contribution of recipient platelets and monocytes.
  
  
  METHODS
  Primary pig aortic endothelial cells (PAECs) were incubated with combinations of fresh or heat-inactivated human plasma, platelets, or monocytes, after which they were separated and analyzed individually by flow cytometry for tissue factor (TF) expression and for their ability to clot recalcified normal or factor-VII-deficient plasma.
  
  
  RESULTS
  Procoagulant porcine TF was induced in PAECs only by fresh human plasma, and not by heat-inactivated plasma, platelets, or monocytes. In contrast, procoagulant human TF was induced on platelets and monocytes after incubation with PAEC, irrespective of whether the plasma was present or not. In addition, human platelets caused the shedding of procoagulant TF-expressing aggregates from PAEC.
  
  
  CONCLUSIONS
  This work defines a cell-based in vitro assay system to address complex interactions among PAECs, human platelets, and monocytes. The induction of procoagulant TF on PAECs by fresh human plasma was most likely dependent on xenoreactive natural antibody and complement present in fresh human plasma. In contrast, the shedding of procoagulant platelet-PAEC aggregates, induced by human platelets, and the induction of procoagulant TF on human platelets and monocytes by PAEC, occurred independently of these factors. These results suggest that different mechanisms may contribute to the initiation of thrombosis after xenotransplantation, some of which may not be influenced by the further manipulation of the immune response against pig xenografts.
authors.affiliation: Department of Immunology, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Chih Che
authors.initials: CC
authors.lastname: Lin
authors.forename: Daxin
authors.initials: D
authors.lastname: Chen
authors.forename: John H
authors.initials: JH
authors.lastname: McVey
authors.forename: David K C
authors.initials: DK
authors.lastname: Cooper
authors.forename: Anthony
authors.initials: A
authors.lastname: Dorling
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001011:Aorta; D017209:Apoptosis; D001777:Blood Coagulation; D001792:Blood Platelets / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D005434:Flow Cytometry; D016027:Heart Transplantation; D006801:Humans; D009000:Monocytes / Q000502:physiology*; D010215:Papio; D013552:Swine; D013925:Thromboplastin / Q000096:biosynthesis* / Q000276:immunology; D014183:Transplantation, Heterologous
chemical_list: D000906:Antibodies; D013925:Thromboplastin
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