The infection-exclusive proteome of extracellular vesicles defines bacterial-induced immune response signatures

Extracellular vesicles (EVs) are small, lipid bi-layered structures released from various cell-types throughout the body. These structures are responsible for the delivery of proteins., compounds, and communication signals across spatial distances. EVs are highly important to diverse biological processes within mammalian systems, including roles in cellular maintenance and homeostasis of physiological conditions and response to infection. In this study, we characterize phenotypic traits and proteome remodeling of host EVs derived during a state of infection by the human bacterial pathogen, Klebsiella pneumoniae, compared to an uninfected control. Phenotypic profiling defines consistent size, diameter, and number of EVs from samples across infectious states, whereas a closer look into molecular regulation at the protein level defines core and infection-exclusive proteomes. Within the core proteome (i.e., protein detection common between plasma from uninfected versus infected samples) clustering based on infectious state was observed and significant changes in fibrinogen production with heighted levels upon infection were reported. Conversely, assessment of the infection-exclusive EV proteome highlighted the stark production of immune-associated proteins by Gene Ontology Biological Processes and an enrichment of proteins associated with blood microparticles, membrane-bound, and the extracellular region by Gene Ontology Cellular Compartment. Overall, this study emphasizes complex reprogramming of the EV proteome upon exposure to K. pneumoniae within a murine model of infection and proposes protein-level signatures indicative of bacterial infection.