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1.  Inhibition of Spleen Tyrosine Kinase Prevents Mast Cell Activation and Airway Hyperresponsiveness 
Rationale: Spleen tyrosine kinase (Syk) is important for Fc and B-cell receptor–mediated signaling.
Objective: To determine the activity of a specific Syk inhibitor (R406) on mast cell activation in vitro and on the development of allergen-induced airway hyperresponsiveness (AHR) and inflammation in vivo.
Methods: AHR and inflammation were induced after 10 d of allergen (ovalbumin [OVA]) exposure exclusively via the airways and in the absence of adjuvant. This approach was previously established to be IgE, FcɛRI, and mast cell dependent. Alternatively, mice were passively sensitized with OVA-specific IgE, followed by limited airway challenge. In vitro, the inhibitor was added to cultures of IgE-sensitized bone marrow–derived mast cells (BMMCs) before cross-linking with allergen.
Results: The inhibitor prevented OVA-induced degranulation of passively IgE-sensitized murine BMMCs and inhibited the production of interleukin (IL)-13, tumor necrosis factor α, IL-2, and IL-6 in these sensitized BMMCs. When administered in vivo, R406 inhibited AHR, which developed in BALB/c mice exposed to aerosolized 1% OVA for 10 consecutive d (20 min/d), as well as pulmonary eosinophilia and goblet cell metaplasia. A similar inhibition of AHR was demonstrated in mice passively sensitized with OVA-specific IgE and exposed to limited airway challenge.
Conclusion: This study delineates a functional role for Syk in the development of mast cell– and IgE-mediated AHR and airway inflammation, and these results indicate that inhibition of Syk may be a target in the treatment of allergic asthma.
doi:10.1164/rccm.200503-361OC
PMCID: PMC2662982  PMID: 16192454
airway hyperresponsiveness; eosinophils; goblet cell metaplasia; mast cells; spleen tyrosine kinase
2.  Requirement for Leukotriene B4 Receptor 1 in Allergen-induced Airway Hyperresponsiveness 
Rationale: Leukotriene B4 (LTB4) is a rapidly synthesized, early leukocyte chemoattractant that signals via its cell surface receptor, leukotriene B4 receptor 1 (BLT1), to attract and activate leukocytes during inflammation. A role for the LTB4–BLT1 pathway in allergen-induced airway hyperresponsiveness and inflammation is not well defined. Objectives: To define the role of the LTB4 receptor (BLT1) in the development of airway inflammation and altered airway function. Methods: BLT1-deficient (BLT1−/−) mice and wild-type mice were sensitized to ovalbumin by intraperitoneal injection and then challenged with ovalbumin via the airways. Airway responsiveness to inhaled methacholine, bronchoalveolar lavage fluid cell composition and cytokine levels, and lung inflammation and goblet cell hyperplasia were assessed. Results: Compared with wild-type mice, BLT1−/− mice developed significantly lower airway responsiveness to inhaled methacholine, lower goblet cell hyperplasia in the airways, and decreased interleukin (IL)-13 production both in vivo, in the bronchoalveolar lavage fluid, and in vitro, after antigen stimulation of lung cells in culture. Intracellular cytokine staining of lung cells revealed that bronchoalveolar lavage IL-13 levels and numbers of IL-13+/CD4+ and IL-13+/CD8+ T cells were also reduced in BLT1−/− mice. Reconstitution of sensitized and challenged BLT1−/− mice with allergen-sensitized BLT1+/+ T cells fully restored the development of airway hyperresponsiveness. In contrast, transfer of naive T cells failed to do so. Conclusion: These data suggest that BLT1 expression on primed T cells is required for the full development of airway hyperresponsiveness, which appears to be associated with IL-13 production in these cells.
doi:10.1164/rccm.200502-205OC
PMCID: PMC2718465  PMID: 15849325
airway responsiveness; cytokines; lipid mediators; lung inflammation; T cells

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