A characteristic feature of asthma is inflammation of large airways. Particular attention has been given to the eosinophil, because of its prevalence in inflamed airways of asthmatics and because its products are associated with bronchoconstriction, bronchial hyperresponsiveness, and respiratory epithelial damage. Leukocyte recruitment is multistep process thought to involve the sequential action of selectins, activating signals, and leukocyte integrins. The selectins initiate and sustain the rolling of leukocytes on the endothelium. The counter-receptors for the selectins are carbohydrate- based ligands on the opposed cells. Specific soluble or endothelial- associated signals cause activation of leukocyte integrins, leading to firm arrest of the leukocyte. Extravasation of the leukocyte into the tissue site is the final step. In the case of asthma, information is significantly lacking with respect to selectin involvement and the nature of the leukocyte activation signals. The following specific aims will focus on the role of selectins in the pathophysiology of asthma with emphasis on eosinophil recruitment: 1) Using a mouse model of acute asthma, we will determine whether treatment of animals with antibodies to the three selectins, used singly and in combination, will limit leukocyte recruitment and the development of bronchial hyperreactivity. 2) We will identify cytokine-induced endothelial ligands for L-selectin by using a recombinant L-selectin molecule as an affinity probe. These ligands may have relevance to the ligands on venular endothelium in vivo, which support L-selectin dependent rolling of leukocytes. 3) Using activation-dependent mAbs and functional adhesion assays, we will determine which of the known chemoattractants and priming factors for eosinophils produce a rapid increase in the avidity of their Beta1 and Beta2 integrins. We will also determine the role of L-selectin as a signal transduction molecule in the regulation of integrin avidity on the eosinophil. These studies are anticipated to increase our knowledge of leukocyte recruitment mechanisms in asthma and potentially lead to new therapeutic approaches for the treatment of this disease.
