Abstract
Immunity to pathogens exists as a fine balance between promoting activation and expansion of effector cells, while simultaneously limiting normal and aberrant responses. These seemingly opposing functions are kept in check by immune regulators. The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that senses nutrient availability and, in turn, regulates cell metabolism, growth, and survival accordingly. mTOR plays a pivotal role in facilitating immune defense against invading pathogens by regulating the differentiation, activation, and effector functions of lymphoid cells. Here, we focus on the emerging and sometimes contradictory roles of mTOR in orchestrating lymphoid cell-mediated host immune responses to pathogens. A thorough understanding of how mTOR impacts lymphoid cells in pathogen defense will provide the necessary base for developing therapeutic interventions for infectious diseases.
Highlights
Specialty section: This article was submitted to Microbial Immunology, a section of the journal Frontiers in Immunology
Mechanistic target of rapamycin functions as two signaling complexes in mammalian cells: mechanistic target of rapamycin (mTOR) complex 1 and mTOR complex 2 (Figure 1). mTORC1 includes a scaffolding protein, regulatory-associated protein of mTOR (Raptor), DEP-containing mTOR interacting protein (Deptor), mammalian lethal with Sec13 protein, and the Proline-Rich AKT substrate (PRAS40)
CD8 effector T cell-specific Tsc2 deletion Vaccinia-OVA Excessive generation of effector CD8+ T cells, mTORC1 promotes generation of effectors to enhance mTORC1 unable to differentiate into memory cells
Summary
MTOR complex 1 is activated in response to various extracellular stimuli including nutrients, growth factors, stress, cytokines, and antigen receptor signaling When nutrients and these stimuli are readily available, mTORC1 activity is high, and energy-demanding cellular processes such as translation and ribosomal biogenesis are promoted. When energy and nutrients are readily available, mTOR is active and signals downstream pathways to generate new cellular material to promote cell growth and proliferation, while suppressing autophagy. L. monocytogenes and Salmonella attempt to subvert induction of autophagy by reactivating mTOR to downregulate the immune response [24, 27] These pathogens hijack and maintain basal levels of autophagy to exploit host energy supplies and nutrients for their own replication.
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