During pathogenic influenza virus infection, robust cytokine production (cytokine storm), excessive inflammatory infiltrates, and virus-induced tissue destruction all contribute to morbidity and mortality. Earlier we reported that modulation of sphingosine-1-phosphate-1 receptor (S1P 1 R) signaling provided a chemically tractable approach for the effective blunting of cytokine storm, leading to the improvement of clinical and survival outcomes. Here, we show that S1P 1 R agonist treatment suppresses global cytokine amplification. Importantly, S1P 1 R agonist treatment was able to blunt cytokine/chemokine production and innate immune cell recruitment in the lung independently of endosomal and cytosolic innate sensing pathways. S1P 1 R signaling suppression of cytokine amplification was independent of multiple innate signaling adaptor pathways for myeloid differentiation primary response gene 88 (MyD88) and IFN-β promoter stimulator-1 signaling, indicating a common pathway inhibition of cytokine storm. We identify the MyD88 adaptor molecule as responsible for the majority of cytokine amplification observed following influenza virus challenge.pathology | pulmonary O verabundant innate immune responses correlate with increased morbidity and mortality during multiple pathogenic respiratory viral infections (1-5). When studying human pandemic H1N1/2009 influenza virus in mice and ferrets, we found direct evidence that cytokine storm was chemically tractable using a sphingosine-1-phosphate receptor-1 (S1P 1 R) selective agonists. S1P 1 R agonist therapy suppressed innate immune cell recruitment, cytokine-chemokine production, and improved survival without altering viral clearance, indicating that cytokine storm was causative to disease pathogenesis and that S1P therapy could suppress detrimental innate immune responses without hindering virus control (6, 7). The identification that S1P 1 R agonists suppress detrimental innate immune responses without hindering virus control indicates that S1P 1 R probes may serve as both viable drug leads to curb influenza virus morbidity and mortality, and as research tools to identify additional cellular signaling pathways that can be targeted to improve clinical outcomes during respiratory viral infection.To generate a molecular understanding how S1P 1 R agonist therapy effectively blunts pathological innate inflammatory responses, we systematically assessed the role various innate signaling pathways play in S1P 1 R-mediated suppression of inflammation following influenza virus infection. Using an S1P 1 R selective agonist synergistically with genetic and biochemical tools, we reveal that S1P 1 R signaling effectively suppressed global cytokine amplification at a point that converged downstream of multiple innate signaling pathways. We reveal that S1P 1 R signaling can suppress innate cellular recruitment and cytokine amplification downstream of both endosome and cytosolic innate sensing pathways. Moreover, we identify myeloid differentiation primary response gene 88 (MyD88) as the ...

Summary Although type I interferon (IFN-I) is thought to be beneficial against microbial infections, persistent viral infections are characterized by high interferon signatures suggesting that IFN-I signaling may promote disease pathogenesis. During persistent lymphocytic choriomeningitis virus (LCMV) infection, IFNα and IFNβ are highly induced early after infection and blocking IFN-I receptor (IFNAR) signaling promotes virus clearance. We assessed the specific roles of IFNβ versus IFNα in controlling LCMV infection. While blockade of IFNβ alone does not alter early viral dissemination, it is important in determining lymphoid structure, lymphocyte migration, and anti-viral T cell responses that lead to accelerated virus clearance, approximating what occurs during attenuation of IFNAR signaling. Comparatively, blockade of IFNα was not associated with improved viral control but with early dissemination of virus. Thus, despite their use of the same receptor, IFNβ and IFNα have unique and distinguishable biologic functions, with IFNβ being mainly responsible for promoting viral persistence.

The ongoing COVID-19 pandemic is caused by SARS-CoV-2, which is rapidly evolving with better transmissibility. Understanding the molecular basis of the SARS-CoV-2 interaction with host cells is of paramount significance, and development of antiviral agents provides new avenues to prevent and treat COVID-19 diseases. This study describes a molecular characterization of innate immune evasion mediated by the SARS-CoV-2 Nsp5 main protease and subsequent development of a small-molecule inhibitor.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolves rapidly under the pressure of host immunity, as evidenced by waves of emerging variants despite effective vaccinations, highlighting the need for complementing antivirals. We report that targeting a pyrimidine synthesis enzyme restores inflammatory response and depletes the nucleotide pool to impede SARS-CoV-2 infection. SARS-CoV-2 deploys Nsp9 to activate carbamoyl-phosphate synthetase, aspartate transcarbamoylase, and dihydroorotase (CAD) that catalyzes the rate-limiting steps of the de novo pyrimidine synthesis. Activated CAD not only fuels de novo nucleotide synthesis but also deamidates RelA. While RelA deamidation shuts down NF-κB activation and subsequent inflammatory response, it up-regulates key glycolytic enzymes to promote aerobic glycolysis that provides metabolites for de novo nucleotide synthesis. A newly synthesized small-molecule inhibitor of CAD restores antiviral inflammatory response and depletes the pyrimidine pool, thus effectively impeding SARS-CoV-2 replication. Targeting an essential cellular metabolic enzyme thus offers an antiviral strategy that would be more refractory to SARS-CoV-2 genetic changes.

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