Transient targeting of phosphoinositide 3-kinase acts as a roadblock in mast cells' route to allergy

BACKGROUND: Tissue mast cell numbers are dynamically regulated by recruitment of progenitors from the vasculature. It is unclear whether progenitors are recruited during allergic sensitization and whether recruitment promotes allergic responses. OBJECTIVE: We sought to (1) determine the effect of mast cell recruitment on acute allergic responses and (2) to define the role of phosphoinositide 3-kinase (PI3K) isoforms in sequential steps to allergic responses. METHODS: Gene-targeted mice for PI3Kgamma or PI3Kdelta or mice treated with isoform-specific PI3K inhibitors (a novel PI3Kgamma-specific inhibitor [NVS-PI3-4] and the PI3Kdelta inhibitor IC87114) were used to monitor IgE-mediated mast cell recruitment, migration, adhesion by means of intravital microscopy, degranulation, TNF-alpha release, and subsequent endothelial cell activation in vivo or in bone marrow-derived mast cells. RESULTS: Functional PI3Kgamma, but not PI3Kdelta, was crucial for mast cell accumulation in IgE-challenged skin, TNF-alpha release from IgE/antigen-stimulated mast cells, and mast cell/endothelial interactions and chemotaxis. PI3Kgamma-deficient bone marrow-derived mast cells did not adhere to the endothelium in TNF-alpha-treated cremaster muscle, whereas PI3Kdelta was not required. Depletion of TNF-alpha blocked IgE-induced mast cell recruitment, which links tissue mast cell-derived cytokine release to endothelial activation and mast cell recruitment. Interference with mast cell recruitment protected against anaphylaxis and was superior to blockage of tissue mast cell degranulation. CONCLUSIONS: Interference with mast cell recruitment to exacerbated tissues provides a novel strategy to alleviate allergic reactions and surpassed attenuation of tissue mast cell degranulation. This results in prolonged drug action and allows for reduction of drug doses required to block anaphylaxis, an important feature for drugs targeting inflammatory disease in general.