title: The role of C1q in recognition of apoptotic epithelial cells and inflammatory cytokine production by phagocytes during Helicobacter pylori infection.
abstract: BACKGROUND
  Gastric epithelial cells (GECs) undergo apoptosis during H. pylori infection and phagocytes within the mucosa engulf these cells. The recognition and clearance of apoptotic cells is a multifactorial process, enhanced by the presence of various bridging molecules and opsonins which are abundant in serum. However, it is not clear how recognition or clearance may differ in the context of H. pylori infection induced apoptosis. In addition, efferocytosis of sterile apoptotic cells is known to confer anti-inflammatory properties in the engulfing phagocyte, however it is unknown if this is maintained when phagocytes encounter H. pylori-infected cells. Thus, the ability of macrophages to bind and engulf gastric epithelial cells rendered apoptotic by H. pylori infection and the association of these interactions to the modulation of phagocyte inflammatory responses was investigated in the absence and presence of serum with a particular focus on the role of serum protein C1q.
  
  
  METHODS
  Control (uninfected) or H. pylori-infected AGS cells were co-cultured with THP-1 macrophages in the presence or absence of serum or serum free conditions + C1q protein (40-80 μg/mL). Binding of AGS cells to THP-1 macrophages was assessed by microscopy and cytokine (IL-6 and TNF-α) release from LPS stimulated THP-1 macrophages was quantified by ELISA.
  
  
  RESULTS
  We show that macrophages bound preferentially to cells undergoing apoptosis subsequent to infection with H. pylori. Binding of apoptotic AGS to THP-1 macrophages was significantly inhibited when studied in the absence of serum and reconstitution of serum-free medium with purified human C1q restored binding of macrophages to apoptotic cells. Co-culture of sterile apoptotic and H. pylori-infected AGS cells both attenuated LPS-stimulated cytokine production by THP-1 macrophages. Further, direct treatment of THP-1 macrophages with C1q attenuated LPS stimulated TNF-α production.
  
  
  CONCLUSIONS
  These studies suggest that C1q opsonizes GECs rendered apoptotic by H. pylori. No differences existed in the ability of infected or sterile apoptotic cells to attenuate macrophage cytokine production, however, there may be a direct role for C1q in modulating macrophage inflammatory cytokine production to infectious stimuli.
authors.affiliation: Department of Pathology, University of California, La Jolla, San Diego, CA USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fox
authors.affiliation: Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA ; National University Ireland, Galway, Ireland.
authors.forename: Kieran A
authors.initials: KA
authors.lastname: Ryan
authors.affiliation: Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA ; Broad Institute of MIT and Harvard, Boston, MA USA.
authors.forename: Alice H
authors.initials: AH
authors.lastname: Berger
authors.affiliation: Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA ; Athersys, Inc, Cleveland, OH USA.
authors.forename: Katie
authors.initials: K
authors.lastname: Petro
authors.affiliation: Department of Pathology, University of California, La Jolla, San Diego, CA USA ; Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA.
authors.forename: Soumita
authors.initials: S
authors.lastname: Das
authors.affiliation: Department of Pathology, University of California, La Jolla, San Diego, CA USA ; Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA.
authors.forename: Sheila E
authors.initials: SE
authors.lastname: Crowe
authors.affiliation: Department of Pathology, University of California, La Jolla, San Diego, CA USA ; Division of Gastroenterology and Hepatology, University of Virginia, Charlottesville, VA USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Ernst
keywords: Binding; C1q; Cytokines; Epithelial cell; H. pylori; Macrophage