GUARDIANS · Guard-driven immunity against pathogens

Successful pathogens use virulence factors to inhibit immune defenses. To counteract this, host guard proteins monitor the integrity of pathways (guardees) that are attacked by virulence factors, such that inhibition of the guardee activates guard-driven immunity. Instead of directly detecting microbial components like canonical innate immune (pattern recognition) receptors, guards are activated by sensing the activity of virulent microbes. While guard-immunity is common in plants, only a few mammalian guard-pathways are known and mammals are thought to heavily rely on pattern recognition to detect pathogens. We have recently described the MORC3-MRE pathway, the first mammalian guard-sensing pathway that recognizes the virulence- associated activity of viruses to induce a protective interferon (IFN) response. I hypothesize that mammalian guard-sensors are highly relevant for both immune homeostasis and immunity and propose to test this hypothesis by focusing on the MORC3-MRE pathway. Utilizing genetic approaches in human monocytes and mice, we will reveal novel components and molecular mechanisms of the MORC3-MRE pathway and investigate its role in homeostasis and immunity in vivo. The main hypothesis of this proposal is that guard- sensing allows mammalian immune cells to broadly recognize the activities of virulence factors. We aim to conduct forward genetic screens in human monocytes to identify virulence-associated activities of pathogens that are sensed by the immune system. Functional genomics and biochemical approaches will identify the attacked guardee, the guard-sensor and molecular mechanism of guard-sensing. In summary, we will experimentally test the novel concept of guard-immunity in mammalian immune defenses. These experiments will generate fundamentally new insights into molecular mechanisms of pathogen recognition and will significantly broaden our understanding of innate immunity and host-pathogen interactions.