MECHANISMS AND CONSEQUENCES OF EOSINOPHIL ACTIVATION WITHIN AIRWAYS

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Studies are proposed to determine the mechanisms by which immune activation and adhesion of eosinophils are translated into augmented bronchomotor tone as occurs in human asthma. Through a collaboration established by the Lung Institute of NHLBI and the Research ministry of the Republic of Germany, a method has been developed to assess the effects of activated human eosinophils on microsections of explanted human bronchial airways. These studies utilize using a newly developed technique for videomicrometry and on-line computerized integration of airway lumenal diameter in 250 microl microwell chambers. A central hypothesis of these investigations is that adhesion to endothelium and/or cellular matrix primes eosinophils for release of inflammatory mediators that cause augmented airway smooth muscle contraction. In an initial series of experiments, studies will be performed to assess the mechanism by which prolonged exposure of eosinophils (greater than or equal to 24 h) to myeloma protein IgE and/or interleukin (IL)-4 causes upregulation of the native secretory response to stimulation by antigenic cross linking using a novel anti-IgE antibody (TN142). These studies examine the hypothesis that immune stimulation per se is an initial priming event in the activation of eosinophils during endothelial transmigration. In a second series of studies, the augmenting effect of inflammatory cell binding to endothelium on the bronchoconstriction caused by immune- and pharmacologically activated eosinophils will be examined. Preliminary studies indicate that ligation to human umbilical cord vein endothelial cells (HUVEC) causes upregulated secretion of eosinophils and augmented narrowing of human bronchial explants. Further studies will examine the specific ligands responsible for this augmented narrowing and a mechanism for selective blockade of this response. In a third series of studies, the effect of eosinophil binding to the matrix protein, fibronectin, through the surface ligand VLA-4 also will be examined. Preliminary investigations indicate that this is an extremely slow binding process that confers sustained augmentation of eosinophil secretory activity. Studies are proposed to examine directly the effects of this prolonged binding on the contractile response elicited by immunologically activated eosinophils on human bronchial explants and to determine the mechanism of this augmented contraction through selective blockage with monoclonal antibodies to specific cell surface ligands, e.g., anti-VLA-4 (HP 2/1). In each investigation, the role of the low affinity CD23 receptor, FcepsilonRII, in activating eosinophil secretion and consequent airway contractility will be examined, and the relationship between the upregulation of this receptor caused by exposure to rhIL-4 and IgE will be assessed. Comparable studies will be done using pharmacological activation with exogenous platelet activating factor, and the potential role for direct immune regulation of bronchial contraction through the low affinity eosinophil IgE receptor will be examined. All essential methodologies for proposed studies have been developed in preliminary studies for this proposal. Data derived from these studies should elucidate mechanisms by which an unusual (eosinophilic) mode of inflammation confers hyperresponsiveness upon human bronchial airways as occurs in human asthma.