Investigating Pulmonary Immune Responses that Detect and Counteract Gram-negative Bacterial Infections

Infections of the lungs can cause tremendous tissue damage which often leads to pathogens spreading into the bloodstream. In the airways, Gram-negative bacteria produce biofilms through exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on detection remains uncertain. Using genome-engineered P. aeruginosa strains, we compared EPS-producers versus non-producers and a virulent E. coli pneumonia model in mice to better understand detection. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness mediated by TRPV1+ TLR4+ sensory neuron detection of the exposed lipopolysaccharide (LPS). Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Once bacteria enter the bloodstream, an immune paradox occurs where host responses counteract the invading pathogen but also contribute to devastating organ damage and death. During E. coli bacteremia, we observed in vivo pulmonary neutrophil and platelet interactions that resulted in immunothrombosis. Intravital microscopy and novel single cell behavioral analysis revealed that cathelicidin initiated neutrophil swarming and clustering, which preceded LTB4 dependent immunothrombosis. These immunothrombi trapped bacteria and promoted platelet dependent microbial resistance but also caused lethal vascular occlusions. Cathelicidin deficiency impaired this host defence mechanism leading to bacterial overgrowth that resulted in delayed sepsis mortality. Altogether, this thesis uncovers how Gram-negative bacteria evade neuronal detection, how the host counteracts them in the bloodstream, and how these insights may guide strategies to enhance host defence while reducing pathology.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Medicine – Immunology

Grantor

Cumming School of Medicine

Year dc:date.issued

2025

Author dc:creator

• Brown, Luke

Advisor dc:contributor.advisor

• Yipp, Bryan G.

Committee members dc:contributor.committeemember

• McKay, Derek
• Baron, Rebecca

• Neuroimmune
• Neuroinflammation
• Sensory neurons
• Nociceptors
• Psuedomonas aeruginosa
• Biofilms
• Hypothalamus
• Paraventricular nuclei
• Corticotropin-releasing hormona
• Infectious disease
• Immunopathology
• Immunothrombosis
• NETosis
• Sepsis
• Escherichia coli
• Neutrophil
• Platelet
• Cathelicidin
• Leukotriene B4
• Formyl-peptide receptor
• Behaviouromic
• Intravital microscopy
• Lungs
• Bloodstream infection

Statement dc:rights

• Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

en

DOI

https://dx.doi.org/10.11575/PRISM/50666

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:1880/123110