title: C1q- and collectin-dependent phagocytosis of apoptotic host cells by the intestinal protozoan Entamoeba histolytica.
abstract: BACKGROUND
  Entamoeba histolytica, the cause of invasive amebiasis, phagocytoses apoptotic host cells during tissue invasion. In mammals, collectin family members (e.g., mannose-binding lectin [MBL]) and the structurally related protein C1q bind to apoptotic cells and stimulate macrophage phagocytosis via a conserved collagenous tail domain. The collectins also bind to bacteria, the usual source of nutrients for E. histolytica.
  
  
  METHODS
  To test the possibility that the collectins are ligands that stimulate E. histolytica phagocytosis, we used a flow cytometry-based assay for amebic phagocytosis, a method for making single-ligand particles to delineate a given ligand's ability to initiate phagocytosis, and purified human C1q, MBL, and collagenous collectin tails.
  
  
  RESULTS
  Apoptotic lymphocytes opsonized with serum or human C1q were phagocytosed more efficiently than control cells, an effect that was dependent on ligand density. C1q and the collectins alone were adequate to trigger amebic phagocytosis, because single-ligand particles coated with C1q, MBL, or purified collectin tails were phagocytosed more efficiently than control particles. Furthermore, C1q, MBL, and the tail domain of C1q were all chemoattractants for E. histolytica.
  
  
  CONCLUSIONS
  C1q and MBL can serve as opsonins on apoptotic cells that stimulate E. histolytica phagocytosis, an effect mediated at least in part by the collagenous collectin tail domain.
authors.affiliation: Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05405, USA.
authors.forename: Jose Eduardo
authors.initials: JE
authors.lastname: Teixeira
authors.forename: Bradley Thomas
authors.initials: BT
authors.lastname: Heron
authors.forename: Christopher Dwight
authors.initials: CD
authors.lastname: Huston
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D037222:Collectins / Q000502:physiology*; D015922:Complement C1q / Q000502:physiology*; D004748:Entamoeba histolytica / Q000276:immunology*; D006801:Humans; D037601:Mannose-Binding Lectin / Q000502:physiology; D010587:Phagocytosis
chemical_list: D037222:Collectins; D037601:Mannose-Binding Lectin; D015922:Complement C1q