Type I interferons determine innate resistance to Listeria

Type I interferons (IFN-I) form a group of cytokines, proteins produced during an infection and regulating the immune response. Typically IFN-I are made during an infection with intracellular pathogens like viruses where they increase innate resistance of the host organism. Listeria monocytogenes is a Gram-positive bacterium endowed with the ability to invade cells of an infected host and use them as vehicels for its replication. Recognition of the intracellular bacteria by the innate immune system causes IFN-I production similar as in the case of viral infection. Unlike viral infection the biological impact of IFN-I is not generally protective against Listeria monocytogenes. Upon systemic infection of mice with the bacterial pathogen IFN-I production causes a reduced ability to cope with the invader. This results in an IFN-I-mediated increase in lethal infection. The preliminary work for our proposal demonstrates that the immunological effect of IFN-I is determined by the route of infection a bacterial pathogen chooses to invade its host. We were able to show that contrasting systemic infection entry of Listeria monocytogenes into the host organism via its natural route of infection through the gastrointestinal tract causes a protective impact of IFN-I on innate resistance. It is therefore the aim of the described experimental approaches to investigate the influence of the infection route on the ensuing immune response. We are particularly interested in determining the cells and mechanisms by which different infection routes produce contrasting IFN-I effects on innate immunity. To this end we will carry out a comprehensive analysis of the immune responses after gastrointestinal or systemic infection of mice with Listeria monocytogenes and have a close look at the role of IFN-I in increasing damage of infected organs. Using mouse genetics we will reveal which cell types cause protective or adverse effects on innate immunity to Listeria monocytogenes by responding to IFN-I. Finally we will carry out comprehensive analyses of bacterial as well as host gene expression to characterize the genes determining protective or adverse IFN-I effects. Our studies will uncover causal relationships between the infection route of a pathogen and the immune response directed against this pathogen. They will further help to clarify why IFN-I can both exacerbate or heal pathological processes. Particular relevance to such studies comes from the fact that IFN-I are applied clinically against both infectious and chronic inflammatory disease.

Interferons (IFN) are mediators of the innate immune system. They are released when the immune system combats infectious microorganisms. Based on their interaction with different plasma membrane receptors IFN are divided into three different types. Type I IFN are mainly the IFN and IFN, type II IFN is the IFN and type III IFN are the IFN. The three IFN types have overlapping, but distinct tasks in the immune system. In our project we were predominantly concerned with the role of type I IFN in innate immunity to a bacterial pathogen, Listeria monocytogenes. Our previous work had identified type I IFN as adverse when applied through parenteral routes, but neutral or even beneficial when applied via the gastrointestinal tract. Here we addressed cellular and molecular mechanisms contributing to the synthesis of IFN during infection with L. monocytogenes (subproject 1), or to the synthesis of gene products in response to signaling from the type I IFN receptor (subproject 2). Finally, we studied in detail the role of a molecule involved in gene induction by type I and type III IFN called IRF9 (subproject 3). In subproject 1 we investigated the role of an enzyme involved in RNA metabolism, DDX3X. Surprisingly, DDX3X is also involved in the control of gene transcription. Our findings in mice lacking the Ddx3x gene in hematopoietic cells reveal a role of DDX3X beyond IFN synthesis. These mice were highly susceptible to L. monocytogenes infection owing to alterations in the hematopoietic cell compartment and in the transcriptional response to infection, including type I IFN synthesis. Interestingly, the DDX3X defect shows a strong gender component. Female mice dont survive deletion in hematopoietic cells and die during embryogenesis. In contrast, male mice survive due to the presence of a DDX3X paralogue on the Y chromosome called DDX3Y. Our studies demonstrate functional redundancy between DDX3X and DDX3Y, explaining the survival of male mice. The studies raise the possibility that DDX3X and DDX3Y may contribute to differences between male and female immune systems. In subproject 2 we investigated the effect of pharmacological inhibition of the transcriptional regulator Brd4. We demonstrated an important role for the expression of IFN- induced genes in response to L. monocytogenes infection. Mice treated with the inhibitor were highly susceptible to infection. This result may be of relevance, for the clinical application of Brd4 inhibitors. Studies of subproject 3 demonstrated unexpected functions of IRF9 during L. monocytogenes infection or during experimental colitis. Whereas IRF9 is thought to function in responses to type I and type III IFN, we revealed an additional role in the transcriptional response to IFN. Furthermore, our data indicate a regulatory role of IRF9 in shaping the immunemetabolism during infection with L. monocytogenes.