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Airway inflammation and airway hyperresponsiveness are central issues in the pathogenesis of asthma. CD69 is a membrane molecule transiently expressed on activated lymphocytes, and its selective expression in inflammatory infiltrates suggests that it plays a role in the pathogenesis of inflammatory diseases. In CD69-deficient mice, OVA-induced eosinophilic airway inflammation, mucus hyperproduction, and airway hyperresponsiveness were attenuated. Cell transfer of Ag-primed wild-type but not CD69-deficient CD4 T cells restored the induction of allergic inflammation in CD69-deficient mice, indicating a critical role of CD69 expressed on CD4 T cells. Th2 responses induced by CD69-deficient CD4 T cells in the lung were attenuated, and the migration of CD4 T cells into the asthmatic lung was severely compromised. The expression of VCAM-1 was also substantially altered, suggesting the involvement of VCAM-1 in the CD69-dependent migration of Th2 cells into the asthmatic lung. Interestingly, the administration of anti-CD69 Ab inhibited the induction of the OVA-induced airway inflammation and hyperresponsiveness. This inhibitory effect induced by the CD69 mAb was observed even after the airway challenge with OVA. These results indicate that CD69 plays a crucial role in the pathogenesis of allergen-induced eosinophilic airway inflammation and hyperresponsiveness and that CD69 could be a possible therapeutic target for asthmatic patients.