Infected-Host-Cell Repertoire and Cellular Response in the Lung following Inhalation ofFrancisella tularensisSchu S4, LVS, or U112

Abstract

Francisella tularensis causes systemic disease in humans and other mammals, with high morbidity and mortality associated with inhalation-acquired infection. F. tularensis is a facultative intracellular pathogen, but the scope and significance of cell types infected during disease is unknown. Using flow cytometry, we identified and quantified infected-cell types and assessed the impact of infection on cell populations following inhalation of F. tularensis strains U112, LVS, and Schu S4. Initially, alveolar macrophages comprised over 70% of Schu S4-and LVS-infected cells, whereas approximately 51% and 27% of U112-infected cells were alveolar macrophages and neutrophils, respectively. After 3 days, roughly half of Schu S4-and LVS-and nearly 80% of U112-infected cells were neutrophils. All strains infected CD11b high macrophages, dendritic cells, monocytes, and alveolar type II cells throughout infection. Macrophage, monocyte, and dendritic-cell populations were reduced during U112 infection but not Schu S4 or LVS infection. These results demonstrate directly that F. tularensis is a promiscuous intracellular pathogen in the lung that invades and replicates within cell types ranging from migratory immune cells to structural tissue cells. However, the proportions of cell types infected and the cellular immune response evoked by the human pathogenic strain Schu S4 differ from those of the human avirulent U112.Since 2001, there has been increased interest in understanding pathogens with virulence characteristics that make them dangerous for purposeful release. One such organism is the gram-negative bacterium Francisella tularensis, the etiological agent of tularemia. Virulent strains of Francisella can cause incapacitating or lethal disease in humans, mice, and other mammals (24). Tularemia can be acquired via insect bites (13), by handling infected animal carcasses (30), from contaminated water (11), or by inhalation (15). Inhalation exposure results in the most-acute, rapidly progressing manifestation of disease (6). When inhaled, as few as 10 organisms can cause a debilitating, and potentially fatal, infection in humans (22).Given the seriousness of inhalation-acquired tularemia, surprisingly little is known about Francisella biology in the host lung. Within 1 hour after inhalation, Francisella is found in airway macrophages and dendritic cells (DCs) (3, 4). However, the infection of these cells does not trigger production of tumor necrosis factor alpha or interleukin-6 (3, 4). Instead, Francisella infection induces immunosuppressive mediators, such as transforming growth factor ␤ (TGF-␤) (3) and prostaglandin E2 (31), through yet-unknown mechanisms. F. tularensis also infects other cell types important for host defense against lung infections, such as monocytes (23), neutrophils (16), and alveolar type II (ATII) epithelial cells (10).Growth within host cells is recognized as an important aspect of Francisella pathogenesis; however, the range and scope of cells infected throughout disease in an animal host have not b...

Identification of a Novel Francisella tularensis Factor Required for Intramacrophage Survival and Subversion of Innate Immune Response

“…1G). Several recent studies have highlighted the differences between the pathogenesis of F. novicida, LVS, and SchuS4 strain (63)(64)(65) and have shown that infection of mice or macrophages with the former strain results in rapid induction of proinflammatory cytokines, whereas these responses are extremely muted after infection with the latter two strains. F. novicida, which was used as a positive control in intramacrophage lysis studies, underwent significantly higher lysis as compared with F. tularensis LVS or FTL_0325 mutant.…”

Lung CD4−CD8− Double-Negative T Cells Are Prominent Producers of IL-17A and IFN-γ during Primary Respiratory Murine Infection with Francisella tularensis Live Vaccine Strain

“…Because IL-17Rs are expressed on a wide variety of cell types, including leukocytes and epithelial cells, and many of these cell types can support the growth of Francisella species (13,32,33), we investigated the direct impact of IL-17A on control of LVS growth in host cells. Interestingly, we found that IL-17A can cooperate with IFN-g to inhibit growth of LVS in alveolar epithelial cells and macrophages.…”

IL-27/IFN-γ Induce MyD88-Dependent Steroid-Resistant Airway Hyperresponsiveness by Inhibiting Glucocorticoid Signaling in Macrophages

“…Cells were then washed and immediately stained for surface marker expression using the following fluorescent mAbs: anti-F4/80, anti-CD11b, and anti-CD11c (BD Pharmingen, San Diego, CA). Subpopulations of pulmonary macrophages were categorized as previously described (46 …”