IFN-?, but not IL-17A, is required for survival during secondary pulmonary Francisella tularensis Live Vaccine Stain infection

Abstract

IL-17 and IFN-γ production by Th17 and Th1 cells, respectively, is critical for survival during primary respiratory infection with the pathogenic bacterium, Francisella tularensis Live Vaccine Strain (LVS). The importance, however, of these T cell subsets and their soluble mediators is not well understood during a secondary or memory response. We measured the number of CD4+ T cells producing IFN-γ or IL-17 in the spleen and lungs of vaccinated mice on day four of the secondary response using intracellular cytokine staining in order to identify protective T cell subsets participating in the memory response. Few bacteria were present in spleens of vaccinated mice on day four and a T cell response was not observed. In the lung, where more bacteria were present, there was a robust Th1 response in vaccinated mice but Th17 cells were not present at higher numbers in vaccinated mice compared to unvaccinated mice. These data show that the lung is the dominant site of the secondary immune response and suggest that Th17 cells are not required for survival during secondary challenge. To further investigate the importance of IFN-γ and IL-17 during the secondary response to F. tularensis, we neutralized either IFN-γ or IL-17 in vivo using monoclonal antibody treatment. Vaccinated mice treated with anti-IFN-γ lost more weight and had higher bacterial burdens compared to vaccinated mice treated with isotype control antibody. In contrast, treatment with anti-IL-17A antibody did not alter weight loss profiles or bacterial burdens compared to mice treated with isotype control antibody. Together, these results suggested that IFN-γ is required during both primary and secondary respiratory F. tularensis infection. IL-17, on the other hand, is only critical during the primary response to respiratory F. tularensis but dispensable during the secondary response.

TLR2 Signaling is Required for the Innate, but Not Adaptive Response to LVS clpB

“…Despite LVS clpB ’s attenuation, it elicits a robust T-cell response and previous infection with LVS clpB protects 100% of mice challenged with a lethal dose of LVS (15, 20). We were therefore interested in whether TLR2, a key host sensor for detecting Francisella , was required during the various phases of the immune response to LVS clpB .…”

Development of a novelFrancisella tularensisLive Vaccine Strain expressing ovalbumin provides insight intoFrancisella tularensis-specific CD8+T cell responses

“…Activated CD8 + T cells are capable of producing a range of cytokines depending on inflammatory cues and transcriptional programing [33,34]. Among these, IFN-γ is known to play an important role in activating phagocytic cells to kill many intracellular pathogens, including F. tularensis [35–37]. The role of IL-17A in the immune response to F. tularensis has been studied, but has been more difficult to define, and appears to vary based on F. tularensis strain, route of exposure, and primary versus recall response [37–40].…”

“…Among these, IFN-γ is known to play an important role in activating phagocytic cells to kill many intracellular pathogens, including F. tularensis [35–37]. The role of IL-17A in the immune response to F. tularensis has been studied, but has been more difficult to define, and appears to vary based on F. tularensis strain, route of exposure, and primary versus recall response [37–40]. To study the production of these two representative cytokines by Francisella -specific CD8 + T cells, we performed intracellular cytokine staining on cells isolated from LVS-OVA-infected animals and stimulated with PMA/calcium ionophore.…”

Inclusion of Epitopes That Expand High-Avidity CD4+ T Cells Transforms Subprotective Vaccines to Efficacious Immunogens against Virulent Francisella tularensis

“…Poly-functional T cells, defined by their ability to produce multiple effector cytokines, such as IFN-γ and TNF-α, are important for CD4 + and CD8 + T cells to mediate pathogen control (21–24). IFN-γ and TNF-α are required to survive infection with attenuated Francisella (25–29) and IFN- γR deficient mice succumb in a convalescent model of SchuS4 infection (12). To further confirm the requirement for multiple cytokines in control of SchuS4, we compared the ability of IFN-γ, TNF-α, and IFN-γ plus TNF-α to control bacterial replication in vitro .…”