STING/MPYS mediates host defense against Listeria monocytogenes infection by regulating Ly6C(hi) monocyte migration.

MPYS (also known as STING, MITA, and TMEM173) is a type I IFN stimulator that is essential for host defense against DNA virus infection and appears important in defense against certain bacteria. The in vivo significance and mechanisms by which MPYS mediates host defense against nonviral pathogens are unknown. Using an MPYS-deficient mouse (Tmem173()), we determined that, distinct from the IFNAR(-/-) mice, MPYS deficiency leads to increased bacterial burden in the liver upon Listeria monocytogenes infection. The increase was correlated with the diminished MCP-1 and MCP-3 chemokine production and decreased blood and liver Ly6C(hi) monocyte frequency. We further demonstrate that MPYS-deficient Ly6C(hi) monocytes are intrinsically defective in migration to the liver. Lastly, adoptive transfer of wild-type Ly6C(hi) monocyte into MPYS-deficient mice decreases their liver bacterial burden. Our findings reveal a novel in vivo function of MPYS that is distinct from its role in activating type I IFN production.

MPYS is required for IFN response factor 3 activation and type I IFN production in the response of cultured phagocytes to bacterial second messengers cyclic-di-AMP and cyclic-di-GMP.

Cyclic-di-GMP and cyclic-di-AMP are second messengers produced by bacteria and influence bacterial cell survival, differentiation, colonization, biofilm formation, virulence, and bacteria-host interactions. In this study, we show that in both RAW264.7 macrophage cells and primary bone marrow-derived macrophages, the production of IFN-ß and IL-6, but not TNF, in response to cyclic-di-AMP and cyclic-di-GMP requires MPYS (also known as STING, MITA, and TMEM173). Furthermore, expression of MPYS was required for IFN response factor 3 but not NF-κB activation in response to these bacterial metabolites. We also confirm that MPYS is required for type I IFN production by cultured macrophages infected with the intracellular pathogens Listeria monocytogenes and Francisella tularensis. However, during systemic infection with either pathogen, MPYS deficiency did not impact bacterial burdens in infected spleens. Serum IFN-ß and IL-6 concentrations in the infected control and MPYS(-/-) mice were also similar at 24 h postinfection, suggesting that these pathogens stimulate MPYS-independent cytokine production during in vivo infection. Our findings indicate that bifurcating MPYS-dependent and -independent pathways mediate sensing of cytosolic bacterial infections.

Transient Receptor Potential Melastatin 2 (TRPM2) ion channel is required for innate immunity against Listeria monocytogenes.

The generation of reactive oxygen species (ROS) is inherent to immune responses. ROS are crucially involved in host defense against pathogens by promoting bacterial killing, but also as signaling agents coordinating the production of cytokines. Transient Receptor Potential Melastatin 2 (TRPM2) is a Ca(2+)-permeable channel gated via binding of ADP-ribose, a metabolite formed under conditions of cellular exposure to ROS. Here, we show that TRPM2-deficient mice are extremely susceptible to infection with Listeria monocytogenes (Lm), exhibiting an inefficient innate immune response. In a comparison with IFNγR-deficient mice, TRPM2(-/-) mice shared similar features of uncontrolled bacterial replication and reduced levels of inducible (i)NOS-expressing monocytes, but had intact IFNγ responsiveness. In contrast, we found that levels of cytokines IL-12 and IFNγ were diminished in TRPM2(-/-) mice following Lm infection, which correlated with their reduced innate activation. Moreover, TRPM2(-/-) mice displayed a higher degree of susceptibility than IL-12-unresponsive mice, and supplementation with recombinant IFNγ was sufficient to reverse the unrestrained bacterial growth and ultimately the lethal phenotype of Lm-infected TRPM2(-/-) mice. The severity of listeriosis we observed in TRPM2(-/-) mice has not been reported for any other ion channel. These findings establish an unsuspected role for ADP-ribose and ROS-mediated cation flux for innate immunity, opening up unique possibilities for immunomodulatory intervention through TRPM2.