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.