Bordetella pertussis is an obligate human pathogen that colonizes the ciliated respiratory epithelium of its host to cause the disease pertussis, which is the least controlled of all vaccine-preventable infectious diseases. In the US, from 2012-2014, there were 24,231 - 48,277 pertussis cases reported annually. The resurgence of pertussis has been attributed to use of acellular vaccines, which are thought to provide inadequate protection and may not effectively prevent colonization. The conventional approach, focused on B. pertussis virulence gene products as potential vaccine components, has not been successful. A major hindrance to preventing pertussis is our lack of knowledge of the in vivo biology, physiology, and metabolism of B. pertussis. Iron starvation is a known host environmental cue that strongly influences bacterial gene expression and protein production. Previous studies have shown that in the host B. pertussis is iron-starved and produces numerous outer membrane iron receptors and other proteins specific to the host environment. Bacterial surface proteins are considered good vaccine candidates because specific antibodies have the potential to prevent colonization and enhance immune recognition. However, studies using host convalescent and immune sera to identify B. pertussis proteins produced in vivo typically use screening antigens prepared from B. pertussis cells grown in iron- and nutrient-rich culture media. As a result, the bacteria are not iron starved nor will they have produced their iron receptors or other iron repressed proteins that are naturally made in vivo - potentially important antigens will not be detected. This project is centered on cell surface proteins produced by B. pertussis cells grown in a host, or in conditions that simulate the host environment. Surface proteins that are immunoreactive with infected host convalescent sera and are required for growth in the host environment will be identified. These proteins may be receptors for iron or other nutrients, adhesins, porins or other surface-exposed proteins. Protein candidates will be functionally characterized and tested as protective antigens in mouse respiratory infections. Analysis of B. pertussis proteins produced in the context of pertussis infection will increase our understanding of its growth in the human host and aid our ability to interfere with that process.