Mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2-dependent pathways are essential for CD8⁺ T cell-mediated airway hyperresponsiveness and inflammation

Background: Ligation of the leukotriene B₄ (LTB₄) receptor 1 on effector memory CD8⁺ T cells by LTB₄ is important for the recruitment of CD8⁺ T cells into the airways, which appears central to the induction of airway hyperresponsiveness (AHR) and allergic inflammation. Phosphorylation of extracellular signal-regulated kinase (ERK) is important in activation and cytokine production from many cell types. Objective: The roles of ERKs in effector CD8⁺ T-cell function and on CD8⁺ T cell-mediated AHR were determined. Methods: Effector CD8⁺ T cells were generated from OVA_257-264 (SIINFEKL) peptide-primed mononuclear cells from OT-1 mice. The effects of U0126, an ERK inhibitor, on effector CD8⁺ T-cell function and on CD8⁺ T cell-mediated AHR and allergic inflammation were examined. Results: Pretreatment of effector CD8⁺ T cells with U0126 suppressed anti-CD3/anti-CD28-induced ERK1/2 phosphorylation and cytokine production, but did not affect LTB₄-induced Ca²⁺ mobilization or chemotaxis. Adoptive transfer of U0126-treated CD8⁺ T cells into sensitized mice before secondary allergen challenge resulted in significant decreases in AHR, eosinophilic inflammation, goblet cell metaplasia, and IL-5 and IL-13 levels in bronchoalveolar lavage fluid of recipient mice. The number of transferred CD8⁺ T cells accumulating in bronchoalveolar lavage fluid or lungs was unaffected by treatment. Conclusion: ERK1/2-dependent pathways are essential for the effector functions of CD8⁺ T cells, including T_H2 cytokine production, allergic inflammation, and development of AHR. Inhibition of ERK1/2 signaling has potential therapeutic benefit in preventing CD8⁺ T cell-mediated AHR.