Cell-Based Screen Identifies Human Interferon-Stimulated Regulators of <i>Listeria monocytogenes</i> Infection

<div><p>The type I interferon (IFN) activated transcriptional response is a critical antiviral defense mechanism, yet its role in bacterial pathogenesis remains less well characterized. Using an intracellular pathogen <i>Listeria monocytogenes</i> (<i>Lm</i>) as a model bacterial pathogen, we sought to identify the roles of individual interferon-stimulated genes (ISGs) in context of bacterial infection. Previously, IFN has been implicated in both restricting and promoting <i>Lm</i> growth and immune stimulatory functions <i>in vivo</i>. Here we adapted a gain-of-function flow cytometry based approach to screen a library of more than 350 human ISGs for inhibitors and enhancers of <i>Lm</i> infection. We identify 6 genes, including <i>UNC93B1</i>, <i>MYD88</i>, <i>AQP9</i>, and <i>TRIM14</i> that potently inhibit <i>Lm</i> infection. These inhibitors act through both transcription-mediated (MYD88) and non-transcriptional mechanisms (TRIM14). Further, we identify and characterize the human high affinity immunoglobulin receptor FcγRIa as an enhancer of <i>Lm</i> internalization. Our results reveal that FcγRIa promotes <i>Lm</i> uptake in the absence of known host <i>Lm</i> internalization receptors (E-cadherin and c-Met) as well as bacterial surface internalins (InlA and InlB). Additionally, FcγRIa-mediated uptake occurs independently of <i>Lm</i> opsonization or canonical FcγRIa signaling. Finally, we established the contribution of FcγRIa to <i>Lm</i> infection in phagocytic cells, thus potentially linking the IFN response to a novel bacterial uptake pathway. Together, these studies provide an experimental and conceptual basis for deciphering the role of IFN in bacterial defense and virulence at single-gene resolution.</p>