Responses to cytosolic DNA are a central component of both infectious diseases, where they are the first line of detection and defense to DNA viruses and intracellular bacteria, and autoinflammatory diseases that result from chronic inflammatory response to cellular self-DNA. A mechanistic understanding of these responses is key to leverage them to treat both types of diseases. In particular, we have preliminary data that challenge the dogma that type I interferon (IFN-I) is the only response to cytosolic DNA. Specifically, we have seen that macrophages from multiple wild-derived mouse strains, which are genetically divergent from inbred laboratory mice, only produce low levels of IFN-I in response to cytosolic DNA and to a DNA virus, murine herpesvirus 68 (MHV68). Instead, they produce high levels of the inflammatory cytokine IL-6. These strains include CAST and PWK, which were used to derive the collaborative cross (CC) lines. Based on these data, we hypothesized that in order to avoid excessive inflammation mediated by IFN-I, alternative DNA response pathways have evolved to complement IFN-I production, perhaps with less dangerous substitutes such as IL-6. Since these novel responses are regulated by yet-unknown factors, we propose to map, clone, and characterize novel regulators of responses to cytosolic DNA, critical for our understanding of the balanced host response to DNA pathogens. Our central approach will be positional cloning of the regulators using CC (Collaborative Cross) mice as a genetic model. Such a plan will meet the purpose of the CC initiative, which was intended to provide tools for instant mapping of genetic traits. To achieve these goals, we have assembled a team with synergistic expertise, including an immunogeneticist with a long track-record in studying DNA responses using mouse genetics in evolutionarily divergent mice (Dr. Poltorak) and two microbiologists with expertise in the biology of pathogens that can cause foreign DNA presence in the cytoplasm, in particular herpesviruses, including MHV68 (Dr. M. Gaglia), and Mycobacterium tuberculosis (Dr. S. Tan). In the first Aim, we will determine which strains of the CC mice respond to cytosolic DNA in vitro with low IFN-I but high IL-6. We will map genetic loci responsible for this alternative response and further narrow down these intervals using a genetic screen in an F2 intercross (C57BL/6 x CAST/or PWK). This line of investigation will ultimately lead to a list of candidate genes (loci) responsible for the control of IL-6 and IFN-I induction, which we will test individually by gene silencing and overexpression.
In Aim 2, we will use macrophages from select CC lines with differential production of IL-6 and IFN-I to examine in vitro responses to MHV68 and M. tuberculosis and investigate how they affect pathogen replication. This will help determine the potential benefits of the combined IFN-I and IL-6 response we see in the wild-derived mice. By investigating the mechanism of DNA responses in CC mice, we aim to provide better insight into the mechanistic regulation of responses to infection pathologies present in human patients with interferonopathies. ! !
Responses to pathogen-derived cytosolic DNA lead to production of type I Interferon (IFN-I), an important regulator in defense against infectious diseases and immune-related pathology. Based on published reports and our preliminary data, however, we hypothesize that in response to DNA, production of IFN-I may not be the default outcome and that other pathways are activated and contribute to immune responses and inflammation. We will identify genomic loci responsible for regulation of responses to cytosolic DNA in Collaborative Cross mice, and will then confirm importance of the isolated loci in regulation of in vitro responses to two DNA pathogens, MHV68 and M. tuberculosis
