Contribution of Antigen-Primed CD8⁺ T Cells to the Development of Airway Hyperresponsiveness and Inflammation Is Associated with IL-13

The role of Th2/CD4 T cells, which secrete IL-4, IL-5, and IL-13, in allergic disease is well established; however, the role of CD8⁺ T cells (allergen-induced airway hyperresponsiveness (AHR) and inflammation) is less clear. This study was conducted to define the role of Ag-primed CD8 ⁺ T cells in the development of these allergen-induced responses. CD8-deficient (CD8^-/-) mice and wild-type mice were sensitized to OVA by i.p. injection and then challenged with OVA via the airways. Compared with wild-type mice, CD8^-/- mice developed significantly lower airway responsiveness to inhaled methacholine and lung eosinophilia, and exhibited decreased IL-13 production both in vivo, in the bronchoalveolar lavage (BAL) fluid, and in vitro, following Ag stimulation of peribronchial lymph node (PBLN) cells in culture. Reconstitution of sensitized and challenged CD8^-/- mice with allergen-sensitized CD8⁺ T cells fully restored the development of AHR, BAL eosinophilia, and IL-13 levels in BAL and in culture supernatants from PBLN cells. In contrast, transfer of naive CD8 ⁺ T cells or allergen-sensitized CD8⁺ T cells from IL-13-deficient donor mice failed to do so. Intracellular cytokine staining of lung as well as PBLN T cells revealed that CD8⁺ T cells were a source of IL-13. These data suggest that Ag-primed CD8⁺ T cells are required for the full development of AHR and airway inflammation, which appears to be associated with IL-13 production from these primed T cells.