Dominant Suppression of Early Innate Immune Mechanisms by Yersinia pestis

Disease progression of primary pneumonic plague is biphasic, consisting of a pre-inflammatory and a pro-inflammatory phase. Most lung pathogens induce a measureable inflammatory response within a few hours of infection, but <italic>Yersinia pestis</italic> is strikingly different: the first 36 hours of infection are characterized by rapid bacterial replication in the lung without generating appreciable levels of proinflammatory cytokines/chemokines, histological changes in infected tissue or outward disease symptoms. The ultimate goal of this thesis was to understand the processes that contribute to the pre-inflammatory phase of disease. Upon inhalation of infectious droplets, <italic>Y. pestis</italic> can interact with a myriad of different cell types, but the initial bacterial / host cell interactions during pulmonary infection are largely uncharacterized. I found that <italic>Y. pestis</italic> cannot be lavaged from the lung during the initial stages of infection but is freely lavageable during the later stages of infection, indicating that <italic>Y. pestis</italic> adheres tightly to lung tissues during the pre-inflammatory phase of disease. Although recent studies have implicated Ail as the <italic>Y. pestis</italic> adhesin that mediates this interaction, my data suggest that Ail acts to stabilize the outer membrane, and the loss of Ail alters other outer membrane proteins. Interestingly, the reintroduction of two major Yersinia adhesins, yadA and inv, into <italic>Y. pestis</italic> reduces the virulence of <italic>Y. pestis</italic> in both bubonic and pneumonic animal models of infection, offering an explanation as to why these genes were lost during the course of <italic>Y. pestis</italic> evolution. I also developed a negative selection screen termed transposon site hybridization: TraSH) to identify bacterial factors required for the two different phases of <italic>Y. pestis</italic> pulmonary infection. I validated the technique by defining the essential genes for <italic>Y. pestis</italic> viability, which largely coincided with essential genes found in <italic>Escherichia coli</italic>. However, I was unable to identify any known virulence factors using TraSH following an intranasal infection, including genes involved in the Ysc type-three secretion system: T3SS), which are known to be essential for pulmonary infection, suggesting that there is global trans-complementation of attenuated mutants by wild-type <italic>Y. pestis</italic>. Finally, using a co-infection model of pneumonic plague, I discovered that <italic>Y. pestis</italic> quickly creates a localized, dominant anti-inflammatory state that allows for the survival and rapid growth of both itself and normally avirulent organisms. In contrast, <italic>Y. pseudotuberculosis</italic>, the relatively recent progenitor of <italic>Y. pestis</italic>, and <italic>K. pneumoniae</italic>, another highly virulent lung pathogen, show no similar trans-complementation effect, which is unprecedented among other respiratory pathogens. Both the unbiased negative selection screen using a vast pool of <italic>Y. pestis</italic> mutants: TraSH) and the co-infection experiments revealed no selection against any known virulence genes, demonstrating the transformation of the lung into a globally permissive environment during the pre-inflammatory phase of pneumonic plague that allows not only wild-type <italic>Y. pestis</italic> to proliferate rapidly in the lung, but other microbes as well.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biology and Biomedical Sciences: Molecular Microbiology and Microbial Pathogenesis

Year dc:date.available

2011

Author dc:creator

• Price, Paul

Contributors dc:contributor

• William Goldman

• Microbiology
• Immunology
• Adhesion
• Immune suppression
• Pneumonic plague
• Trans-complementation
• Yersinia pestis

Language dc:language

English (en)

DOI

https://doi.org/10.7936/K71C1TW9

OAI identifier oai:identifier

oai:openscholarship.wustl.edu:etd-1632