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's present address is: Janssen Research and Development, San Diego, California, USA. tional mice. LLB aided with SMARTA transfer experiments and performed microarray analysis. HS received approval, performed, and analyzed human cell-based assays. EIZ conceived the study and supervised the entire project. GML and EIZ wrote the manuscript.

Intestinal barrier leakage constitutes a potential therapeutic target for many inflammatory diseases and represents a disease progression marker during chronic viral infections. However, the causes of altered gut barrier remain mostly unknown. Using murine infection with lymphocytic choriomeningitis virus, we demonstrate that, in contrast to an acute viral strain, a persistent viral isolate leads to long-term viral replication in hematopoietic and mesenchymal cells, but not epithelial cells (IECs), in the intestine. Viral persistence drove sustained intestinal epithelial barrier leakage, which was characterized by increased paracellular flux of small molecules and was associated with enhanced colitis susceptibility. Type I IFN signaling caused tight junction dysregulation in IECs, promoted gut microbiome shifts and enhanced intestinal CD8 T cell responses. Notably, both type I IFN receptor blockade and CD8 T cell depletion prevented infection-induced barrier leakage. Our study demonstrates that infection with a virus that persistently replicates in the intestinal mucosa increases epithelial barrier permeability and reveals type I IFNs and CD8 T cells as causative factors of intestinal leakage during chronic infections.

Correspondence:We introduce a web-enabled small-molecule mass spectrometry (MS) search engine. To date, no tool can query all the public small-molecule tandem MS data in metabolomics repositories, greatly limiting the utility of these resources in clinical, environmental and natural product applications. Therefore, we introduce a Mass Spectrometry Search Tool (MASST) (https://proteosafe-extensions.ucsd.edu/masst/), that enables the discovery of molecular relationships among accessible public metabolomics and natural product tandem mass spectrometry data (MS/MS).The ability to discover related sequences of proteins or genes in publicly accessible sequence data using Basic Local Alignment Search Tool (BLAST), connected to public sequence data repositories through a web interface (WebBLAST, https://blast.ncbi.nlm.nih.gov/Blast.cgi), was introduced in the 1990s. 1 It has garnered more than 138,159 citations according to Google Scholar, placing it among the most widely used bioinformatics tools. WebBLAST enabled detection of the number of sequences in public repositories related to a given query, the organisms in which those sequences occur, and the evolutionary and inferred functional relationships among related sequences. It therefore permitted a broad community to answer simple but scientifically compelling questions such as: Is a protein or DNA sequence common or rare? How is this sequence distributed among different kinds of organisms? What other sequences are related to this sequence (evolutionary variants, or new mutations, or synthetic constructs)? In the early days of making DNA or protein sequence data publicly available, the "metadata" (e.g., contextual information about the sample, population and location the sequence came from, and technical information about how it was produced) in the public repositories was limited and no standards existed. This is a situation similar to the current status of much of the mass spectrometry data in the public domain. However, when publicly deposited data has metadata available, such as organism, location of sampling, host phenotypes such as diseases, etc., it becomes possible to start building higherlevel hypotheses regarding the evolutionary, ecological or functional relationships among these DNA, RNA or protein sequences. The development of the ability to search data with added context continues to have profound impacts on fields including medicine, chemistry, genetics, molecular biology, genomics, microbiology, and ecology.Algorithms developed for mass spectrometry data, including molecular networking 2 and fragmentation trees 3 , enable similarity searches, while powerful metabolomics analysis software infrastructures, such as MS-DIAL 4 , MetaboAnalyst 5 , XCMS Online 6 , HMDB 7 , some of which have been available for over a decade, focus on annotation of MS/MS spectra or finding statistical relationships between molecular features. However, none of the existing tools enable searching against public data in repositories. Finding the distribution of specific data of i...

It is known that a subpopulation of T cells expresses two T cell receptor (TCR) clonotypes, though the extent and functional significance of this is not established. To definitively evaluate dual TCRα cells, we generated mice with green fluorescent protein and red fluorescent protein reporters linked to TCRα, revealing that ∼16% of T cells express dual TCRs, notably higher than prior estimates. Importantly, dual TCR expression has functional consequences, as dual TCR cells predominated response to lymphocytic choriomeningitis virus infection, comprising up to 60% of virus-specific CD4+and CD8+T cells during acute responses. Dual receptor expression selectively influenced immune memory, as postinfection memory CD4+populations contained significantly increased frequencies of dual TCR cells. These data reveal a previously unappreciated contribution of dual TCR cells to the immune repertoire and highlight their potential effects on immune responses.