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The unexpected drop of the Blue Nile water in July 2020, attributed to the sudden closure of the Grand Ethiopian Renaissance Dam (GERD) during the first filling in 2020, significantly interrupted the water supply for Khartoum, Sudan. This incident pursued using satellites and hydrological models to estimate inflows into Roseires dam. A hydrological model was developed to predict GERD inflows, while reservoir levels were extracted from Sentinel-1, -2 and Jason-3. A water balance model was developed to predict GERD releases and the dates of overtopping during subsequent fillings events. The study demonstrates the effectiveness of satellite data and models for transboundary reservoir management.

Tricuspid regurgitation (TR) is a highly prevalent condition and an independent risk factor for adverse outcomes. Multiple clinical guidelines exist for the diagnosis and management of TR, but the recommendations may sometimes vary. We systematically reviewed high-quality guidelines with a specific focus on areas of agreement, disagreement, and gaps in evidence. We searched MEDLINE and EMBASE (1 January 2011 to 30 August 2021), the Guidelines International Network International, Guideline Library, National Guideline Clearinghouse, National Library for Health Guidelines Finder, Canadian Medical Association Clinical Practice Guidelines Infobase, Google Scholar, and websites of relevant organizations for contemporary guidelines that were rigorously developed (as assessed by the Appraisal of Guidelines for Research and Evaluation II tool). Three guidelines were finally retained. There was consensus on a TR grading system, recognition of isolated functional TR associated with atrial fibrillation, and indications for valve surgery in symptomatic vs. asymptomatic patients, primary vs. secondary TR, and isolated TR forms. Discrepancies exist in the role of biomarkers, complementary multimodality imaging, exercise echocardiography, and cardiopulmonary exercise testing for risk stratification and clinical decision-making of progressive TR and asymptomatic severe TR, management of atrial functional TR, and choice of transcatheter tricuspid valve intervention (TTVI). Risk-based thresholds for quantitative TR grading, robust risk score models for TR surgery, surveillance intervals, population-based screening programmes, TTVI indications, and consensus on endpoint definitions are lacking.

The role unconventional T cells play in protective immunity in humans is unclear. Mucosal-associated invariant T (MAIT) cells are an unconventional T cell subset restricted to the antigen-presenting molecule MR1. Here, we report the discovery of a patient homozygous for a rare Arg31His (R9H in the mature protein) mutation in MR1 who has a history of difficult-to-treat viral and bacterial infections. MR1R9H was unable to present the potent microbially derived MAIT cell stimulatory ligand. The MR1R9H crystal structure revealed that the stimulatory ligand cannot bind due to the mutation lying within, and causing structural perturbation to, the ligand-binding domain of MR1. While MR1R9H could bind and be up-regulated by a MAIT cell inhibitory ligand, the patient lacked circulating MAIT cells. This shows the importance of the stimulatory ligand for MAIT cell selection in humans. The patient had an expanded T cell population, indicating a compensatory interplay between these unconventional T cell subsets.Copyright © 2020 American Association for the Advancement of Science. All rights reserved.

Mucosal-associated Invariant T (MAIT) cells recognize vitamin B-based antigens presented by the non-polymorphic MHC class I related-1 molecule (MR1). Both MAIT T cell receptors (TCR) and MR1 are highly conserved among mammals, suggesting an important, and conserved, immune function. For many years, the antigens they recognize were unknown. The discovery that MR1 presents vitamin B-based small molecule ligands resulted in a rapid expansion of research in this area, which has yielded information on the role of MAIT cells in immune protection, autoimmune disease and recently in homeostasis and cancer. More recently, we have begun to appreciate the diverse nature of the small molecule ligands that can bind MR1, with several less potent antigens and small molecule drugs that can bind MR1 being identified. Complementary structural information has revealed the complex nature of interactions defining antigen recognition. Additionally, we now view MAIT cells (defined here as MR1-riboflavin-Ag reactive, TRAV1-2+ cells) as one subset of a broader family of MR1-reactive T cells (MR1T cells). Despite these advances, we still lack a complete understanding of how MR1 ligands are generated, presented and recognized in vivo. The biological relevance of these MR1 ligands and the function of MR1T cells in infection and disease warrants further investigation with new tools and approaches.

The antigen-presenting molecule MR1 (MHC class I-related protein 1) presents metabolite antigens derived from microbial vitamin B2 synthesis to activate mucosal-associated invariant T (MAIT) cells. Key aspects of this evolutionarily conserved pathway remain uncharacterized, including where MR1 acquires ligands and what accessory proteins assist ligand binding. We answer these questions by using a fluorophore-labeled stable MR1 antigen analog, a conformation-specific MR1 mAb, proteomic analysis, and a genome-wide CRISPR/Cas9 library screen. We show that the endoplasmic reticulum (ER) contains a pool of two unliganded MR1 conformers stabilized via interactions with chaperones tapasin and tapasin-related protein. This pool is the primary source of MR1 molecules for the presentation of exogenous metabolite antigens to MAIT cells. Deletion of these chaperones reduces the ER-resident MR1 pool and hampers antigen presentation and MAIT cell activation. The MR1 antigen-presentation pathway thus co-opts ER chaperones to fulfill its unique ability to present exogenous metabolite antigens captured within the ER.

The antigen-presenting molecule MR1 presents riboflavin-based metabolites to Mucosal-Associated Invariant T (MAIT) cells. While MR1 egress to the cell surface is ligand-dependent, the ability of small-molecule ligands to impact on MR1 cellular trafficking remains unknown. Arising from an in silico screen of the MR1 ligand-binding pocket, we identify one ligand, 3-([2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-yl]formamido)propanoic acid, DB28, as well as an analog, methyl 3-([2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-yl]formamido)propanoate, NV18.1, that down-regulate MR1 from the cell surface and retain MR1 molecules in the endoplasmic reticulum (ER) in an immature form. DB28 and NV18.1 compete with the known MR1 ligands, 5-OP-RU and acetyl-6-FP, for MR1 binding and inhibit MR1-dependent MAIT cell activation. Crystal structures of the MAIT T cell receptor (TCR) complexed with MR1-DB28 and MR1-NV18.1, show that these two ligands reside within the A'-pocket of MR1. Neither ligand forms a Schiff base with MR1 molecules; both are nevertheless sequestered by a network of hydrophobic and polar contacts. Accordingly, we define a class of compounds that inhibits MR1 cellular trafficking.