title: Modulation of FcεRI-dependent mast cell response by OX40L via Fyn, PI3K, and RhoA.
abstract: BACKGROUND
  The interaction of mast cells (MCs) with regulatory T cells through the OX40 ligand (OX40L):OX40 axis downregulates FcεRI-dependent immediate hypersensitivity responses both in vitro and in vivo. Little is known on OX40L-mediated intracellular signaling or on the mechanism by which OX40L engagement suppresses MC degranulation.
  
  
  OBJECTIVE
  We explored the role of OX40L engagement on IgE/antigen-triggered MCs both in vitro and in vivo.
  
  
  METHODS
  The soluble form of OX40 molecule was used to selectively trigger OX40L on MCs in vitro and was used to dissect OX40L contribution in an in vivo model of systemic anaphylaxis.
  
  
  RESULTS
  OX40L:OX40 interaction led to the recruitment of C-terminal src kinase into lipid rafts, causing a preferential suppression of Fyn kinase activity and subsequent reduction in the phosphorylation of Gab2, the phosphatidylinositol 3-OH kinase regulatory subunit p85, and Akt, without affecting the Lyn pathway. Dampening of Fyn kinase activity also inhibited RhoA activation and microtubule nucleation, key regulators of MC degranulation. The in vivo administration of a blocking antibody to OX40L in wild-type mice caused enhanced immediate hypersensitivity, whereas the administration of soluble OX40 to regulatory T-cell-depleted or OX40-deficient mice reduced MC degranulation.
  
  
  CONCLUSIONS
  The engagement of OX40L selectively suppresses Fyn-initiated signals required for MC degranulation and serves to limit immediate hypersensitivity. Our data suggest that soluble OX40 can restore the aberrant or absent regulatory T-cell activity, revealing a previously unappreciated homeostatic role for OX40L in setting the basal threshold of MC response.
authors.affiliation: Department of Medical and Biological Sciences, University of Udine, Udine, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Sibilano
authors.forename: Barbara
authors.initials: B
authors.lastname: Frossi
authors.forename: Ryo
authors.initials: R
authors.lastname: Suzuki
authors.forename: Federica
authors.initials: F
authors.lastname: D'Incà
authors.forename: Giorgia
authors.initials: G
authors.lastname: Gri
authors.forename: Silvia
authors.initials: S
authors.lastname: Piconese
authors.forename: Mario P
authors.initials: MP
authors.lastname: Colombo
authors.forename: Juan
authors.initials: J
authors.lastname: Rivera
authors.forename: Carlo E
authors.initials: CE
authors.lastname: Pucillo
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000707:Anaphylaxis / Q000209:etiology; D000818:Animals; D008407:Mast Cells / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000502:physiology*; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008870:Microtubules / Q000502:physiology; D053278:OX40 Ligand; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010750:Phosphoproteins / Q000502:physiology; D010766:Phosphorylation; D051076:Proto-Oncogene Proteins c-fyn / Q000502:physiology*; D017455:Receptors, IgE / Q000502:physiology*; D048069:Tumor Necrosis Factors / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000502:physiology*; D020742:rhoA GTP-Binding Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D008562:Membrane Glycoproteins; D053278:OX40 Ligand; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D051076:Proto-Oncogene Proteins c-fyn; D017455:Receptors, IgE; D048069:Tumor Necrosis Factors; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; C490894:Gab2 protein, mouse; C504586:Tnfsf4 protein, mouse; C494960:Fyn protein, mouse; C526380:RhoA protein, mouse