Performing Department
Immunology & Infectious Diseases
Non Technical Summary
This project focuses on the basic mechanisms behind the development of encephalitis after Listeria monocytogenes infection. A common risk factor for encephalitic listeriosis is the consumption of poor feed by ruminants, especially cattle. Within that poor feed there is likely a mixture of dead and live bacteria which could have a dramatic effect on the initial control of Listeria monocytogenes spread throughout the ruminant. Our hypothesis is that sensing of large quantities of killed bacteria by mast cells results in an aberrant immune response that enables the spread of live Listeria monocytogenes throughout the animal; thus resulting in the establishment of Listeria monocytogenes infection in the brain and the subsequent development of encephalitis. By understanding the basic mechanism behind this process we aim to develop novel therapeutics which could be used to prevent the development of encephalitic listeriosis.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Our overall hypothesis is that mast cells are critical mediators in the detrimental outcome of the combined infection with heat-killed listeria (HKL) and live L. monocytogenes. Both our preliminary data (Figure 1) and published data from our groups demonstrate that mast cells can be activated by L. monocytogenes (Dietrich et al., 2010; Edelson et al., 2004; Gekara and Weiss, 2008), but what role they play in during the lethal synergy between HKL and live L. monocytogenes infection remains unresolved. In this proposal we will test the in vivo relevance of mast cells in the detrimental synergy observed between HKL and live L. monocytogenes infection. The long-term goals are to determine cellular and molecular pathways important in the development of encephalitic listeriosis in order to development novel treatment regiments that could limit ruminant morbidity and mortality associated with such infections.
Project Methods
To determine the role mast cells play in the observed detrimental synergy between simultaneous infection with HKL and live L. monocytogenes, we will make use of the Wsh mouse. The Wsh mouse has an inversion mutation in an upstream regulatory element of the CD117 (c-kit) locus. As a result, Wsh mice lack mast cells after about 10 weeks of age (Grimbaldeston et al., 2005). Importantly, bone marrow-derived mast cells (BMMC) can be engrafted into Wsh mice in order to complement any observed phenotype (Grimbaldeston et al., 2005; Tsai et al., 2005). This cellular complementation system is extremely powerful as one can then determine which factor produced by the mast cells are necessary for the observed phenotype using BMMC from knock-out mice. Through the use of this complementation system numerous studies have shown mast cells to be important in regulating the immune response to bacterial pathogens (Malaviya et al., 1996; Piliponsky et al., 2010; Song et al., 2009). Moreover, it has been shown that mast cells are an important source of early TNFalpha during bacterial infection or treatment with bacterial products (Dawicki et al., 2010; Gekara and Weiss, 2008; Malaviya et al., 1996; Piliponsky et al., 2010; Shelburne et al., 2009). Since Khanna et al found that after HKL administration the marginal zone macrophages (MZM) were destroyed in a TNFalpha-dependent manner within 9 hours (Khanna et al., 2010), we hypothesize that mast cells will be the crucial source of the TNFalpha, similar to other bacterial infections (Dawicki et al., 2010; Gekara and Weiss, 2008; Malaviya et al., 1996; Piliponsky et al., 2010; Shelburne et al., 2009). Thus, we hypothesis that mast cells are the primary source of early TNFalpha after treatment with HKL and their production of TNFalpha plays a central role in the death of the MZM and development of encephalitic listeriosis. By understanding the role of mast cells during HKL + L. monocytogenes co-infection, we hope to uncover a potentially novel pathway that can be targeted to limit encephalitic listeriosis in ruminants.