Francisella tularensis (Ft) is an important human pathogen responsible for causing tularemia in the northern hemisphere. Ft has long been developed as a biological weapon due to its ability to cause severe illness and is now classified as a category A agent by the CDC based on its possible use as a bioterror agent. Very little is known regarding the role and composition of the inflammasome, a cytosolic multi-protein complex, that activates caspase-1 to produce pro-inflammatory cytokines, IL-1? and IL-18 in host defense against virulent Ft strains. Our overall hypothesis is that active repression of inflammasome is essentially required for intracellular survival of Ft. Our studies in the previous funding period demonstrated that Ft represses inflammasome by acting at the level of Toll-Like Receptor 2 (TLR2), by blocking the mediators of inflammasome activation, and most importantly, by preventing the release of bacterial ligands into the host cell cytosol. We further demonstrated that Absent In Melanoma 2 (AIM2)-dependent inflammasome is repressed in macrophages infected with Ft. We used a broad genomic approach to identify Ft encoded factors responsible for repression of inflammasome in infected macrophages. In particular, we characterized several Ft encoded factors that mediate the repression of AIM2- dependent inflammasome. These results strongly suggest that repression of inflammasome by Ft is a multifactorial process and involves the targeting of several signaling components required for priming and activation. However, the molecular mechanisms leading to repression caused by these Ft encoded factors still remain undetermined.
In specific aim 1, we will investigate how these Ft encoded factors exert their suppressive effects at the priming and activation steps of inflammasome. We have also demonstrated that vaccination using mutants of Ft in these factors protect vaccinated mice against challenge with highly virulent and category A agent Ft SchuS4. These results indicate that inflammasome-induced pro-inflammatory cytokines provide a link between innate and adaptive responses. The contribution of inflammasome-induced cytokines, IL-1? and IL-18 in the development of protective adaptive immune responses against Ft is not known.
In specific aim 2, we will establish how repression of inflammasome mediated cytokines impacts the development of adaptive immune responses. Dissecting the mechanisms of inflammasome-induced responses in the clearance of primary infection and their impact on the development of adaptive immune responses required for protection against secondary Ft challenge are highly innovative. An understanding of the mechanisms of repression of inflammasome and how it regulates adaptive immunity against tularemia will result in the development of effective therapeutics and vaccines.

Public Health Relevance

This proposal aims to investigate the immune suppressive mechanisms underlying the fatal human disease tularemia caused by Francisella tularensis, a Category A bioterror agent. The potential of F. tularensis to cause severe infection is due to its ability to suppress the host's innate immune system. The proposed studies will explore how Francisella evades the host innate immune responses and blocks the development of adaptive immune responses required for protection from subsequent infections. Defining the molecular mechanism(s) of suppression of innate immunity and how this impacts adaptive immunity will be an essential first step towards development of immunotherapeutic, as well as effective vaccine strategies to combat this fatal disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Academic Research Enhancement Awards (AREA) (R15)
Project #
2R15AI107698-02
Application #
9232324
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Mukhopadhyay, Suman
Project Start
2013-07-16
Project End
2019-11-30
Budget Start
2016-12-01
Budget End
2019-11-30
Support Year
2
Fiscal Year
2017
Total Cost
Indirect Cost
Name
Albany College of Pharmacy
Department
Social Sciences
Type
Schools of Arts and Sciences
DUNS #
797866969
City
Albany
State
NY
Country
United States
Zip Code
12208
Alqahtani, Maha; Ma, Zhuo; Ketkar, Harshada et al. (2018) Characterization of a Unique Outer Membrane Protein Required for Oxidative Stress Resistance and Virulence of Francisella tularensis. J Bacteriol 200:
Mansour, Ahd A; Banik, Sukalyani; Suresh, Ragavan V et al. (2018) An Improved Tobacco Mosaic Virus (TMV)-Conjugated Multiantigen Subunit Vaccine Against Respiratory Tularemia. Front Microbiol 9:1195
Rabadi, Seham M; Sanchez, Belkys C; Varanat, Mrudula et al. (2016) Antioxidant Defenses of Francisella tularensis Modulate Macrophage Function and Production of Proinflammatory Cytokines. J Biol Chem 291:5009-21
Ma, Zhuo; Russo, Vincenzo C; Rabadi, Seham M et al. (2016) Elucidation of a mechanism of oxidative stress regulation in Francisella tularensis live vaccine strain. Mol Microbiol 101:856-78
Banik, Sukalyani; Mansour, Ahd Ahmed; Suresh, Ragavan Varadharajan et al. (2015) Development of a Multivalent Subunit Vaccine against Tularemia Using Tobacco Mosaic Virus (TMV) Based Delivery System. PLoS One 10:e0130858
Suresh, Ragavan Varadharajan; Ma, Zhuo; Sunagar, Raju et al. (2015) Preclinical testing of a vaccine candidate against tularemia. PLoS One 10:e0124326
Ma, Zhuo; Banik, Sukalyani; Rane, Harshita et al. (2014) EmrA1 membrane fusion protein of Francisella tularensis LVS is required for resistance to oxidative stress, intramacrophage survival and virulence in mice. Mol Microbiol 91:976-95