Chronic lung infection with Pa remains a major cause of morbidity and mortality in CF. Previous data tell us that: a) alveolar macrophages (AM) and the exuberance of neutrophils (PMN) in the CF lung cannot clear Pa; b) antibodies to Pa in the CF lung are poor opsonins possibly due to protease cleavage or altered isotype; c) there are C3 fragments on Pa form CF lungs, but little is known about the specific form (e.g. C3b, C3bi); d) the C3b receptor (CR1) on phagocytes is deficient on CF lung PMNs, probably due to cleavage by elastase, abundant in CF lungs; the C3bi receptor (CR3) is spared; and e) C3bi, but not C3b, is cleaved in a model system by low concentrations of leukocytes elastase. This project will test the hypothesis that elastase int he CF lung also cleaves C3bi form Pa, and that this, coupled with the loss of PMN CR1 and intrinsically low CR1 on AM, causes impaired phagocyte-bacterial interactions that could help perpetuate lung infection in CF. Experiments will 1) evaluate the effects of bacterial and leukocyte elastases on phagocyte bactericidal activities for pa; 2) quantitate C3 and its fragments, C3bi, and C3d on opsonized Pa and measure their cleavage by elastase; 3) measure the ability of elastase inhibitors to protect opsonins and receptors from proteases in CF lung fluid; and 4) compare Pa with other selected bacterial pathogens to determine if its opsonic characteristics amy contribute to Pa's unique role in CF. These studies should clarify the role of elastase as an activity that impairs lung host defenses in CF and suggest new ways to evaluate the therapeutic potential of elastase inhibitors in future clinical trials. This award will allow me gain the expertise in immunochemistry and biochemistry of complement and proteases needed for this project and will provide me with the tools to understand the relationships between infection and lung tissue damage at the molecular level and to develop as an independent investigator in lung host defenses.
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