Identification of Immunologic and Pathologic Parameters of Death versus Survival in Respiratory Tularemia

Abstract

Francisella tularensis can cause severe disseminated disease after respiratory infection. The identification of factors involved in mortality or recovery following induction of tularemia in the mouse will improve our understanding of the natural history of this disease and facilitate future evaluation of vaccine candidate preparations. BALB/c mice were infected intranasally with the live vaccine strain (LVS) of F. tularensis subsp. holarctica and euthanized at different stages of disease to analyze the induction of immune molecules, gross anatomical features of organs, bacterial burdens, and progression of the histopathological changes in lung and spleen. Tissue-specific interleukin-6 (IL-6), macrophage inflammatory protein 2, and monocyte chemotactic protein 1 were immune markers of mortality, while anti-LVS immunoglobulin M and IL-1␤ were associated with survival. Moribund mice had enlarged spleens and lungs, while surviving mice had even more prominent splenomegaly and normal-appearing lungs. Histopathology of the spleens of severely ill mice was characterized by disrupted lymphoid follicles and fragmented nuclei, while the spleens of survivors appeared healthy but with increased numbers of megakaryocytes and erythrocytes. Histopathology of the lungs of severely ill mice indicated severe pneumonia. Lungs of survivors at early time points showed increased inflammation, while at late times they appeared healthy with peribronchial lymphoid aggregates. Our results suggest that host immune factors are able to affect bacterial dissemination after respiratory tularemia, provide new insights regarding the pathological characteristics of pulmonary tularemia leading to systemic disease, and potentially identify immune markers associated with recovery from the disease.

Repression of Inflammasome by Francisella tularensis during Early Stages of Infection

“…11B). Collectively, these findings are consistent with the biphasic nature of innate immune response generated by F. tularensis, which is associated with an early repression followed by an exaggerated response during the later stages of infection (50).…”

Macrophage Proinflammatory Response to Francisella tularensis Live Vaccine Strain Requires Coordination of Multiple Signaling Pathways

“…In a recent study, mice were challenged intranasally with Ft LVS and cytokine levels were measured in the lungs and spleens. Mice that were moribund had significantly higher levels of MIP-2, MCP-1, and IL-6 in both their lungs and spleens compared with mice that survived infection (41). In contrast, at 7 days postinfection, mice that were going to survive Ft LVS challenge had significantly higher concentrations of IL-1␤ in both their lungs and spleens than mice that were moribund (41).…”

“…Mice that were moribund had significantly higher levels of MIP-2, MCP-1, and IL-6 in both their lungs and spleens compared with mice that survived infection (41). In contrast, at 7 days postinfection, mice that were going to survive Ft LVS challenge had significantly higher concentrations of IL-1␤ in both their lungs and spleens than mice that were moribund (41). Furthermore, ASC Ϫ/Ϫ and Caspase-1 Ϫ/Ϫ mice, which fail to produce IL-1␤ in response to F. novicida infection, succumb more quickly and had a higher bacterial organ burden one day after F. novicida challenge than WT mice (20).…”

Neisseria meningitidisPorB, a Toll-Like Receptor 2 Ligand, Improves the Capacity ofFrancisella tularensisLipopolysaccharide To Protect Mice against Experimental Tularemia

“…The mice were inoculated three times, at 2-week intervals, with 10 g of each antigen in a total volume of 100 l/animal. Four weeks after the last immunization, all vaccinated and unvaccinated control mice were anesthetized with ketamine HCl (Fort Dodge Animal Health, Fort Dodge, IA) and xylazine (Lloyd Laboratories, Shenandoah, IA) and infected intranasally with 10 6 CFU of live LVS in 20 l of PBS, as described previously (5). All animals were closely observed until they were completely awake from the anesthesia, and survival was recorded for up to 50 days after infection.…”

“…holarctica LVS (ATCC 29684) was obtained from the CDC, Fort Collins, CO. For LPS extraction, broth cultures of LVS were grown for 3 days in T-soy broth supplemented with 0.1% L-cysteine. For the challenge experiments, LVS was grown as described previously (5). Briefly, after culture on chocolate agar, colonies were scraped off and suspended in sterile phosphate-buffered saline (PBS) to an optical density at 600 nm of 0.3.…”