The influx and activation of inflammatory cells in the airway wall is dependent, in large part, on the local release of inflammatory cytokines. Although much attention has focused on cytokines derived from leukocytes, it is now clear that airway epithelial cells, the most numerous Cell type in the airway wall, are themselves capable of synthesizing and secreting several cytokines that could profoundly influence airway inflammation. In non-epithelial cells, regulation of cytokine gene expression is critically dependent on signals provided from the extracellular matrix via the integrin family of transmembrane receptors. The existence of similar regulation of cytokine gene expression in airway epithelial cells could help to explain the coexistence of airway remodeling and persistent airway inflammation in asthma. We have recently generated lines of mice expressing a null mutation in the beta-6 integrin subunit, a subunit that is restricted in its expression to epithelia, especially in the lung and skin. Mice expressing this mutation develop and reproduce normally, but all have inflammatory cell infiltrates around hair follicles and scattered throughout the lungs and airways, consistent with a role for integrin- derived signals in regulation of inflammatory cell recruitment and/or activation in these sites. In the proposed studies, we will systematically examine the effects of various components of the normal extracellular matrix and of matrix proteins enriched in injured and inflamed airways, on the constitutive and stimulated synthesis and secretion of cytokines known to be synthesized by airway epithelial cells. Once we have determined the effects of various matrix proteins, we will examine the role of various integrins in these responses. For these experiments, we will use blocking anti-integrin antibodies, recombinant fragments of matrix proteins designed to be uniquely recognized by specific airway epithelial integrins, and murine airway epithelial cells derived from mice expressing mutations in integrin genes. Finally, to determine the significance of integrin and matrix-derived cytokine regulation in vivo, we will examine the influx of inflammatory cells, the production of selected cytokines, and the alterations in in vivo airway responsiveness produced when mice deficient in integrins or integrin ligands are challenged acutely or chronically by either immunologic or non-immunologic inflammatory stimuli. Through these studies, we hope to determine how alterations in airway epithelial integrins and/or their ligands could contribute to the chronic airway inflammation that characterizes persistent asthma.
