The continuing HIV/AIDS epidemic and the spread of multi-drug resistant Mycobacterium tuberculosis (Mtb) has perpetuated an epidemic of tuberculosis in human populations around the world. While BCG is used universally as a vaccine, it is not effective in preventing pulmonary tuberculosis. To combat this ongoing worldwide scourge, vaccine development for tuberculosis is a priority. Apoptosis is an innate M? defense mechanism that limits bacterial replication and restricts dispersal of Mtb. Apoptosis also links innate and clonal immunity. DC present bacterial antigens packaged in apoptotic vesicles to T cells, leading to better T cell priming and protection in vivo. How apoptosis is regulated and restricts Mtb replication and whether it can be manipulated to enhance vaccination is the focus of this proposal. Innovation: The role of eicosanoids in immunity to mycobacteria is conserved in fish, mice and humans, highlighting their fundamental importance. Our published work on in vitro infected human M? and on in vivo infected mice establish apoptosis of Mtb infected M? as a critically important host defense mechanism against tuberculosis. The complexity of death pathways in Mtb infected M? has only recently been appreciated. Virulent Mtb induces lipoxin A4 (LXA4), inhibits prostaglandin E2 (PGE2) synthesis, blocks apoptosis, and promotes necrotic M? death. In contrast, PGE2 protects against necrosis and increases apoptosis. Why apoptosis acts as a host defense mechanism is not understood. Here we put forward a new hypothesis that it is not apoptosis per se that leads to control, but instead phagocytosis of Mtb infected apoptotic M? that is the crucial event. We predict: (1) phagocytosis by M? will contain the infection; and (2) phagocytosis by DC will lead to priming of nave T cells. In addition to the eicosanoid pathways, the balance between IL-1 and type I IFN (IFN) is emerging as a second axis that affects innate and clonal immunity. We propose a new model in which LXA4 and IFN, both induced by Mtb, interact to inhibit innate immunity, while PGE2, IL-1 and TNF promote antibacterial immunity.
Aims :
In Aim 1, we will determine how eicosanoids regulate activation of infected macrophages and induce control of intracellular bacterial replication. In particular, we will determine how eicosanoids affect the balance between IL-1 and type I IFN (IFN), which is emerging as a second axis that affects innate and clonal immunity. In the second aim, we will test the hypothesis that it is not apoptosis per se that kills Mtb - rather it is the phagocytosis f infected apoptotic M? that restricts intracellular Mtb growth. Phagocytosis of apoptotic cells, termed efferocytosis, is a major constitutive M? function; however, little is known about its role during infection. Finally, in the third aim, we will determine the relationship between eicosanoids apoptosis and clonal immunity. We hypothesize that the eicosanoid biosynthetic and cell signaling pathways can be pharmacologically manipulated to enhance apoptosis of infected M?. By promoting apoptotic death, we hope to increase the safety and the efficacy of attenuated bacterial vaccines. We believe that a mechanistic understanding of how pro-apoptotic vaccines induce better immunity will lead to the development of better immunization strategies against tuberculosis and other diseases that are using mycobacterial vectors. Summary: A better understanding of how apoptosis and efferocytosis affect innate immunity to Mtb culminating in control of the bacterial replication and stimulation of T cell immunity will improve our understanding of TB pathogenesis and will lead to research into novel therapies.
Pulmonary tuberculosis, a disease caused by Mycobacterium tuberculosis, is a threat to global health. The disease tuberculosis occurs when the immune system is no longer able to contain the infection. This research proposal seeks to understand how the immune system controls the infection. In addition we seek to determine whether the mechanisms that generate T cell immunity can be enhanced to improve the response to vaccines. Since T cell immunity is important for the control of tuberculosis, it is hoped that by understanding features of host resistance, new strategies can be developed for the treatment and prevention of tuberculosis.
| Marakalala, Mohlopheni J; Raju, Ravikiran M; Sharma, Kirti et al. (2016) Inflammatory signaling in human tuberculosis granulomas is spatially organized. Nat Med 22:531-8 |
| Jayaraman, Pushpa; Jacques, Miye K; Zhu, Chen et al. (2016) TIM3 Mediates T Cell Exhaustion during Mycobacterium tuberculosis Infection. PLoS Pathog 12:e1005490 |
| Behar, Samuel M; Baehrecke, Eric H (2015) Tuberculosis: Autophagy is not the answer. Nature 528:482-3 |
| Martin, Constance J; Peters, Kristen N; Behar, Samuel M (2014) Macrophages clean up: efferocytosis and microbial control. Curr Opin Microbiol 17:17-23 |
| Nunes-Alves, Cláudio; Booty, Matthew G; Carpenter, Stephen M et al. (2014) In search of a new paradigm for protective immunity to TB. Nat Rev Microbiol 12:289-99 |
| Behar, Samuel M; Carpenter, Stephen M; Booty, Matthew G et al. (2014) Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus. Semin Immunol 26:559-77 |
| Zhang, Yanjia J; Reddy, Manchi C; Ioerger, Thomas R et al. (2013) Tryptophan biosynthesis protects mycobacteria from CD4 T-cell-mediated killing. Cell 155:1296-308 |
| Jayaraman, Pushpa; Sada-Ovalle, Isabel; Nishimura, Tomoyasu et al. (2013) IL-1? promotes antimicrobial immunity in macrophages by regulating TNFR signaling and caspase-3 activation. J Immunol 190:4196-204 |
| Divangahi, Maziar; Behar, Samuel M; Remold, Heinz (2013) Dying to live: how the death modality of the infected macrophage affects immunity to tuberculosis. Adv Exp Med Biol 783:103-20 |
| Martin, Constance J; Booty, Matthew G; Rosebrock, Tracy R et al. (2012) Efferocytosis is an innate antibacterial mechanism. Cell Host Microbe 12:289-300 |
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