How early-life colonization and subsequent exposure to the microbiota affect long-term tissue immunity remains poorly understood. Here, we show that the development of mucosal-associated invariant T (MAIT) cells relies on a specific temporal window, after which MAIT cell development is permanently impaired. This imprinting depends on early-life exposure to defined microbes that synthesize riboflavin-derived antigens. In adults, cutaneous MAIT cells are a dominant population of interleukin-17A (IL-17A)–producing lymphocytes, which display a distinct transcriptional signature and can subsequently respond to skin commensals in an IL-1–, IL-18–, and antigen-dependent manner. Consequently, local activation of cutaneous MAIT cells promotes wound healing. Together, our work uncovers a privileged interaction between defined members of the microbiota and MAIT cells, which sequentially controls both tissue-imprinting and subsequent responses to injury.

Hepatitis C virus interacts extensively with host factors not only to establish productive infection but also to trigger unique pathological processes. Our recent genome-wide siRNA screen demonstrated that IKKα is a critical host factor for HCV. Here we describe a novel NF-κB-independent and kinase-mediated nuclear function of IKKα in HCV assembly. HCV infection, through its 3’-untranslated region, interacts with DDX3X to activate IKKα, which translocates to the nucleus and induces a CBP/p300-mediated transcriptional program involving SREBPs. This novel innate pathway induces lipogenic genes and enhances core-associated lipid droplet formation to facilitate viral assembly. Chemical inhibitors of IKKα suppress HCV infection and IKKα-induced lipogenesis, offering a proof-of-concept approach for novel HCV therapeutic development. Our results show that HCV commands a novel mechanism to its advantage by exploiting intrinsic innate response and hijacking lipid metabolism, which likely contributes to a high chronicity rate and the pathological hallmark of steatosis in HCV infection.

Although millions of distinct virus species likely exist, only approximately 9000 are catalogued in GenBank's RefSeq database. We selectively enriched for the genomes of circular DNA viruses in over 70 animal samples, ranging from nematodes to human tissue specimens. A bioinformatics pipeline, Cenote-Taker, was developed to automatically annotate over 2500 complete genomes in a GenBank-compliant format. The new genomes belong to dozens of established and emerging viral families. Some appear to be the result of previously undescribed recombination events between ssDNA and ssRNA viruses. In addition, hundreds of circular DNA elements that do not encode any discernable similarities to previously characterized sequences were identified. To characterize these ‘dark matter’ sequences, we used an artificial neural network to identify candidate viral capsid proteins, several of which formed virus-like particles when expressed in culture. These data further the understanding of viral sequence diversity and allow for high throughput documentation of the virosphere.