Regulation of allergic airway inflammation by class I–restricted allergen presentation and CD8 T-cell infiltration

BackgroundCD8 T cells are known to respond to exogenous antigens through cross-presentation. The importance of the CD8 cell response in the lung after inhalation of allergen and its effects on asthmatic inflammation are less clear.ObjectiveWe sought to determine the dynamics, nature, and immunoregulatory activities of the class I CD8 T-cell response to inhaled allergen.MethodsWe studied a murine model of respiratory allergen sensitization, adoptive transfer of transgenic T cells, and flow cytometric analysis of lung infiltrates.ResultsClass I–restricted CD8 T cells responded rapidly to inhaled allergen and dominated the acute infiltration of T cells into the lung after secondary exposure. CD8 cells in the lung expressed a type 1 phenotype and suppressed the systemic IgE response to subsequent immunization. Dendritic cells purified from conducting airways or lung tissue were highly efficient at cross-presentation of antigen into the class I pathway after intranasal challenge. Adoptive transfer of transgenic antigen-specific CD8, but not CD4, cells resulted in increased IL-12 levels and reduced IL-13 and IL-5 levels in bronchoalveolar lavage fluid, coupled with substantially reduced airway eosinophilia after repeated allergen inhalation, a process mimicked by intranasal administration of IL-12 and inhibited by anti–IL-12 antibody.ConclusionThe data suggest that CD8 cells specific for inhaled allergens are generated in draining lymph nodes but suppress allergic airway inflammation through induction of IL-12 in the lung during interaction with respiratory dendritic cells.Clinical implicationsNovel peptide immunotherapeutics targeting the class I–restricted CD8 T-cell response to allergen represent a promising strategy for extrinsic asthma.