α₄-Integrins mediate antigen-induced late bronchial responses and prolonged airway hyperresponsiveness in sheep

Eosinophils and T lymphocytes are thought to be involved in allergic airway inflammation. Both cells express the α₄β₁-integrin, very late antigen-4 (VLA-4, CD49d/CD29); α₄-integrins can promote cellular adhesion and activation. Therefore, we examined the in vivo effects of a blocking anti-α₄ monoclonal antibody, HP 1/2 bronchial responses, airway hyperresponsiveness, inflammatory cell influx, and peripheral leukocyte counts in allergic sheep. Sheep blood lymphocytes, monocytes, and eosinophils expressed α₄ and bound HP 1/2 . In control sheep, Ascaris antigen challenge produced early and late increases in specific lung resistance of 380±42% and 175±16% over baseline immediately and 7 h after challenge, respectively, as well as airway hyperresponsiveness continuing for 14 d after antigen challenge. Treatment with HP 1/2 (1 mg/kg, i.v.) 30 min before antigen challenge did not affect the early increase in specific lung resistance but inhibited the late-phase increase at 5-8 h by 75% (P < 0.05) and inhibited the post-antigen-induced airway hyperresponsiveness at 1, 2, 7, and 14 d (P < 0.05, for each time). Intravenous HP 1/2 given 2 h after antigen challenge likewise blocked latephase airway changes and postchallenge airway hyperresponsiveness. Airway administration of HP 1/2 (16-mg dose) was also effective in blocking these antigen-induced changes. Response to HP 1/2 was specific since an isotypic monoclonal antibody, 1E6, was ineffective by intravenous and aerosol administration. Inhibition of leukocyte recruitment did not totally account for the activity of anti-α₄ antibody since HP 1/2 neither diminished the eosinopenia or lymphopenia that followed antigen challenge nor consistently altered the composition of leukocytes recovered by bronchoalveolar lavage. Because airway administration of HP 1/2 was also active, HP 1/2 may have inhibited cell activation. Reduction of platelet- activating factor-induced eosinophil peroxidase release from HP 1/2 -treated eosinophils supports such a mechanism. These findings indicate a role for α₄-integrins in processes that lead to airway late phase responses and persisting airway hyperresponsiveness after antigen challenge.