IRG1 and Inducible Nitric Oxide Synthase Act Redundantly with Other Interferon-Gamma-Induced Factors To Restrict Intracellular Replication of Legionella pneumophila
Interferon gamma (IFN-gamma) restricts the intracellular replication of many pathogens, but the mechanism by which IFN-gamma confers cell-intrinsic pathogen resistance remains unclear. For example, intracellular replication of the bacterial pathogen Legionella pneumophila in macrophages is potently curtailed by IFN-gamma. However, consistent with prior studies, no individual genetic deficiency that we tested completely abolished IFN-gamma-mediated control. Intriguingly, we observed that the glycolysis inhibitor 2-deoxyglucose (2DG) partially rescued L. pneumophila replication in IFN-gamma-treated macrophages. 2DG inhibits glycolysis and triggers the unfolded protein response, but unexpectedly, it appears these effects are not responsible for perturbing the antimicrobial activity of IFN-gamma. Instead, we found that 2DG rescues bacterial replication by inhibiting the expression of two key antimicrobial factors, inducible nitric oxide synthase (iNOS) and immune-responsive gene 1 (IRG1). Using immortalized and primary macrophages deficient in iNOS and IRG1, we confirmed that loss of both iNOS and IRG1, but not individual deficiency in either gene, partially reduced IFN-gamma-mediated restriction of L. pneumophila. Further, using a combinatorial CRISPR/Cas9 mutagenesis approach, we found that mutation of iNOS and IRG1 in combination with four other genes (CASP11, IRGM1, IRGM3, and NOX2) resulted in a total loss of L. pneumophila restriction by IFN-gamma in primary bone marrow macrophages. Our study defines a complete set of cell-intrinsic factors required for IFN-gamma-mediated restriction of an intracellular bacterial pathogen and highlights the combinatorial strategy used by hosts to block bacterial replication in macrophages.
Price, Jordan V., Daniel Russo, Daisy X. Ji, et al. 2019. "IRG1 and Inducible Nitric Oxide Synthase Act Redundantly with Other Interferon-Gamma-Induced Factors To Restrict Intracellular Replication of Legionella pneumophila." MBIO 10(6): e02629-19.
American Society for Microbiology
Legionella pneumophila, Host-pathogen interactions, Innate immunity, Interferons, Macrophages