title: Agonist activation of f-actin-mediated eosinophil shape change and mediator release is dependent on Rac2.
abstract: BACKGROUND
  Tissue recruitment and activation of eosinophils contribute to allergic symptoms by causing airway hyperresponsiveness and inflammation. Shape changes and mediator release in eosinophils may be regulated by mammalian Rho-related guanosine triphosphatases. Of these, Rac2 is essential for F-actin formation as a central process underlying cell motility, exocytosis, and respiratory burst in neutrophils, while the role of Rac2 in eosinophils is unknown.We set out to determine the role of Rac2 in eosinophil mediator release and F-actin-dependent shape change in response to chemotactic stimuli.
  
  
  METHODS
  Rac2-deficient eosinophils from CD2-IL-5 transgenic mice crossed with rac2 gene knockout animals were examined for their ability to release superoxide through respiratory burst or eosinophil peroxidase by degranulation. Eosinophil shape change and actin polymerization were also assessed by flow cytometry and confocal microscopy following stimulation with eotaxin-2 or platelet-activating factor.
  
  
  RESULTS
  Eosinophils from wild-type mice displayed inducible superoxide release, but at a small fraction (4-5%) of human eosinophils. Rac2-deficient eosinophils showed significantly less superoxide release (p < 0.05, 26% less than wild type). Eosinophils lacking Rac2 had diminished degranulation (p < 0.05, 62% less eosinophil peroxidase) and shape changes in response to eotaxin-2 or platelet-activating factor (with 68 and 49% less F-actin formation, respectively; p < 0.02) compared with wild-type cells.
  
  
  CONCLUSIONS
  These results demonstrate that Rac2 is an important regulator of eosinophil function by contributing to superoxide production, granule protein release, and eosinophil shape change. Our findings suggest that Rho guanosine triphosphatases are key regulators of cellular inflammation in allergy and asthma.
authors.affiliation: Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, Alta., Canada. paige.lacy@ualberta.ca
authors.forename: Paige
authors.initials: P
authors.lastname: Lacy
authors.forename: Lian
authors.initials: L
authors.lastname: Willetts
authors.forename: John D
authors.initials: JD
authors.lastname: Kim
authors.forename: Andrea N
authors.initials: AN
authors.lastname: Lo
authors.forename: Bon
authors.initials: B
authors.lastname: Lam
authors.forename: Emily I
authors.initials: EI
authors.lastname: Maclean
authors.forename: Redwan
authors.initials: R
authors.lastname: Moqbel
authors.forename: Marc E
authors.initials: ME
authors.lastname: Rothenberg
authors.forename: Nives
authors.initials: N
authors.lastname: Zimmermann
mesh_terms: D000199:Actins / Q000819:agonists* / Q000276:immunology*; D000818:Animals; D015550:Cell Degranulation / Q000276:immunology; D048430:Cell Shape / Q000276:immunology; D054423:Chemokine CCL24 / Q000276:immunology*; D004804:Eosinophils / Q000276:immunology* / Q000648:ultrastructure; D005434:Flow Cytometry; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D010972:Platelet Activating Factor / Q000276:immunology*; D016897:Respiratory Burst / Q000276:immunology; D013047:Specific Pathogen-Free Organisms; D013481:Superoxides / Q000276:immunology; D020744:rac GTP-Binding Proteins / Q000276:immunology*; D000097766:RAC2 GTP-Binding Protein
chemical_list: D000199:Actins; D054423:Chemokine CCL24; D010972:Platelet Activating Factor; D013481:Superoxides; D020744:rac GTP-Binding Proteins; D000097766:RAC2 GTP-Binding Protein