title: Heparin enhances uptake of platelet factor 4/heparin complexes by monocytes and macrophages.
abstract: BACKGROUND
  Heparin-induced thrombocytopenia (HIT) is an iatrogenic complication of heparin therapy caused by antibodies to a self-antigen, platelet factor (4) and heparin. The reasons why antibodies form to PF4/heparin, but not to PF4 bound to other cellular glycosaminoglycans are poorly understood.
  
  
  OBJECTIVE
  To investigate differences in cellular responses to cell-bound PF4 and PF4/heparin complexes, we studied the internalization of each by peripheral blood-derived monocytes, dendritic cells and neutrophils.
  
  
  RESULTS
  Using unlabeled and fluorescently-labeled antigen and/or labeled monoclonal antibody to PF4/heparin complexes (KKO), we show that PF4/heparin complexes are taken up by monocytes in a heparin-dependent manner and are internalized by human monocytes and dendritic cells, but not by neutrophils. Complexes of PF4/low-molecular-weight heparin and complexes composed of heparin and murine PF4, protamine or lysozyme are internalized similarly, suggesting a common endocytic pathway. Uptake of complexes is mediated by macropinocytosis, as shown by inhibition using cytochalasin D and amiloride. Internalized complexes are transported intact to late endosomes, as indicated by co-staining of vesicles with KKO and lysosomal associated membrane protein-2 (LAMP-2). Lastly, we show that cellular uptake is accompanied by expression of MHCII and CD83 co-stimulatory molecules.
  
  
  CONCLUSIONS
  Taken together, these studies establish a distinct role for heparin in enhancing antigen uptake and activation of the initial steps in the cellular immune response to PF4-containing complexes.
authors.affiliation: Division of Hematology, Duke University Medical Center, Durham, NC, USA.
authors.forename: M
authors.initials: M
authors.lastname: Joglekar
authors.affiliation: Division of Hematology, Duke University Medical Center, Durham, NC, USA.
authors.forename: S
authors.initials: S
authors.lastname: Khandelwal
authors.affiliation: Department of Pathology and Laboratory Medicine, Perelman-University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Cines
authors.affiliation: Division of Hematology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Poncz
authors.affiliation: Division of Hematology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: L
authors.initials: L
authors.lastname: Rauova
authors.affiliation: Division of Hematology, Duke University Medical Center, Durham, NC, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Arepally
mesh_terms: D000925:Anticoagulants / Q000276:immunology / Q000378:metabolism / Q000633:toxicity*; D015703:Antigens, CD / Q000378:metabolism; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000187:drug effects / Q000378:metabolism; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D006493:Heparin / Q000276:immunology / Q000378:metabolism / Q000633:toxicity*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D052119:Lysosomal-Associated Membrane Protein 2 / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis / Q000187:drug effects*; D010873:Pinocytosis / Q000187:drug effects*; D010978:Platelet Factor 4 / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding; D013997:Time Factors; D000097802:CD83 Antigen
chemical_list: D000925:Anticoagulants; D015703:Antigens, CD; D006493:Heparin; D000949:Histocompatibility Antigens Class II; D007136:Immunoglobulins; D052119:Lysosomal-Associated Membrane Protein 2; D008562:Membrane Glycoproteins; D010978:Platelet Factor 4; D000097802:CD83 Antigen; C497811:LAMP2 protein, human
keywords: heparin; monocytes; phagocytosis; pinocytosis; platelet factor 4