We have previously demonstrated that the development of allergen-induced airway hyperresponsiveness in a murine model is CD4+ T cell dependent. In the present study, we examined the role of the B7/CD28-CTLA4 costimulatory T cell activation pathway in the pathogenesis of allergen-induced airway hyperresponsiveness in this murine model. Sensitized A/J mice develop significant increases in airway responsiveness, bronchoalveolar lavage eosinophils, serum IgE levels, and Th2-associated cytokine production following aspiration challenge with OVA. Administration of CTLA4-Ig either before Ag sensitization or before pulmonary Ag challenge abolished Ag-induced airway hyperresponsiveness and pulmonary eosinophilia. Examination of cytokine protein levels in the bronchoalveolar lavage showed a significant decrease in the level of the Th2 cytokine, IL-4, after CTLA4-Ig treatment either before sensitization or before challenge, with no significant change in the concentration of the Th1 cytokine, IFN-gamma. Further, the Ag-specific Ab isotypes IgG1 and IgE were significantly decreased in animals treated with CTLA4-Ig before challenge, while there was no significant change in the IgG2a Ab isotype. These data demonstrate that administration of CTLA4-Ig is effective in ablating allergen-induced airway dysfunction concomitant with a significant reduction in the Th2 response. We conclude that B7/CD28-CTLA-4 costimulation is required for the development of many of the immunologic and physiologic features of asthma, possibly by promoting a pathologic type 2-associated response.

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