title: The role of aggregation in Fusobacterium nucleatum- induced immune cell death.
abstract: BACKGROUND
  Fusobacterium nucleatum, an anaerobic oral bacterium, has been shown to be highly abundant in endodontic infections. Its role in these infections remains unclear. Previous studies have shown that F. nucleatum could aggregate immune cells. We have demonstrated that F. nucleatum can induce significant apoptosis in peripheral blood mononuclear cells (PBMCs). In this in vitro study, we sought to determine what role this aggregation phenomenon has on the induction of apoptosis in PBMCs.
  
  
  METHODS
  F. nucleatum bacteria were treated as follows: formaldehyde-fixed, heat-treated, or sonicated before co-culturing with PBMCs. Cell aggregation and apoptosis of the PBMCs were assessed under light microscopy and analyzed by flow cytometry, respectively. PBMCs were then immobilized with a Matrigel matrix before treatment with F. nucleatum. Aggregation and apoptosis were assessed as before. Surface staining of activation marker CD69 was assessed by flow cytometry. The apoptosis and CD69 data underwent one-way analysis of variance, followed by post hoc Bonferroni test and χ(2) test, respectively, to determine statistical significance.
  
  
  RESULTS
  Viable and formaldehyde-treated but not sonicated or heat-treated F. nucleatum bacteria were able to cause severe aggregation and apoptosis of the immune cells. Disruption of F. nucleatum mediated aggregation by immobilization of the cells with a Matrigel matrix resulted in a significant diminution of cell death but not cell activation when assessed by using surface expression of CD69 early activation antigen.
  
  
  CONCLUSIONS
  F. nucleatum's ability to induce cell death in immune cells appears to be mediated through the immune cells being aggregated, which might have important implications for its pathogenesis.
authors: Department of Preventive and Restorative Dental Sciences, Division of Endodontics, University of California, San Francisco, California, USA. tri.huynh@ucsf.edu
authors: Tri
authors: T
authors: Huynh
authors: Radhika V
authors: RV
authors: Kapur
authors: Chris W
authors: CW
authors: Kaplan
authors: Nicholas
authors: N
authors: Cacalano
authors: Susan
authors: S
authors: Kinder Haake
authors: Wenyuan
authors: W
authors: Shi
authors: Peter
authors: P
authors: Sieling
authors: Anahid
authors: A
authors: Jewett
mesh_terms: D000704:Analysis of Variance; D015703:Antigens, CD / Q000276:immunology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology*; D017209:Apoptosis / Q000276:immunology*; D002449:Cell Aggregation / Q000187:drug effects / Q000276:immunology*; D002478:Cells, Cultured; D016009:Chi-Square Distribution; D003094:Collagen / Q000494:pharmacology; D004338:Drug Combinations; D005434:Flow Cytometry; D016967:Fusobacterium nucleatum / Q000276:immunology*; D006801:Humans; D007797:Laminin / Q000494:pharmacology; D037181:Lectins, C-Type / Q000276:immunology*; D007963:Leukocytes, Mononuclear / Q000276:immunology*; D011509:Proteoglycans / Q000494:pharmacology; D018709:Statistics, Nonparametric; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D003094:Collagen; D004338:Drug Combinations; D007797:Laminin; D037181:Lectins, C-Type; D011509:Proteoglycans; D000099192:CD69 Antigens; C059485:matrigel