Airway epithelial cells provide a major immunological function, signaling the presence of potential infectious agents in the airway lumen. The normal function of this surveillance system keeps the airways pristine, whereas abnormalities in epithelial signaling and inflammatory responses contribute significantly to the development of chronic inflammation, characteristic of cystic fibrosis. Epithelial cells are activated by specific bacterial gene products and NF-kB dependent transcription of chemokines and cytokines follows promptly. In the studies proposed, we will examine the molecular mechanisms involved in the immediate response of the epithelium to bacterial gene products and the signaling pathways that accomplish this function. We postulate that common receptor complexes are mobilized to the epithelial cell surface in response to shed bacterial components, activating responses even in the absence of bacteria adherent to the epithelial surface. TLR2, a major receptor for several conserved bacterial components, is co-localized with asialylated glycolipid receptors and similarly mobilized to the cell surface by both gram negative and gram positive pathogens.
The first aim of this project will be to establish the biology of TLR2 in the airway epithelium. To assess the role of TLR2 in airway cells, we will construct a bi-transgenic mouse which has TLR2 expression limited to the lung, to differentiate the contribution of the epithelial cell in signaling the early stages of infection, from the function of """"""""professional"""""""" immune cells, alveolar macrophages and T cells. A comparison of the responses of TLR2 null mice, wild type mice, and mice with TLR2 expression limited to the lung, to both virulent, invasive S. aureus, as opposed to non-invasive mutants which cause pneumonia in CF, but minimal mortality will be done. In the second aim, we will examine the interactions of S. aureus and the airway epithelial cell, focusing specifically on the ability of staphylococcal gene products particularly peptidoglycan and protein A in the activation of the epithelial cells, and their specific activation of TLR2 associated signaling pathways. The role of TLR2 in normal airway epithelial cells and cells with CFTR dysfunction will be compared to determine if excessive activation or impaired regulation of this signaling cascade is associated with the excessive inflammatory response characteristic of cystic fibrosis.
