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Numerical simulations are used to investigate large-scale (mean) magnetic field generation in rotating spherical dynamos. Beyond a certain threshold, we find that the magnitude of the mean magnetic field becomes nearly independent of the system rotation rate and buoyancy forcing. The analysis suggests that this saturation arises from the Malkus-Proctor mechanism in which a Coriolis-Lorentz force balance is achieved in the zonal component of the mean momentum equation. When based on the large-scale magnetic field, the Elsasser number is near unity in the saturated regime. The results show that the large and small magnetic field saturate via distinct mechanisms in rapidly rotating dynamos, and that only the axisymmetric component of the magnetic field appears to follow an Elsasser number scaling.

Macroautophagy/autophagy regulates inflammation via multiple mechanisms, including lysosomal degradation of specific cellular components. Certain autophagy gene “cassettes” also participate in non-canonical processes to mediate important biological activities. While select autophagy genes in myeloid cells have been implicated in protecting mice in models of cytokine storm syndromes (CSS), a more extensive genetic analysis of the autophagy pathway for this disorder has not been reported to date. We determined that multiple canonical autophagy genes in the myeloid compartment protected against fatal disease from both intravenous TNF and intraperitoneal LPS, with the notable exception that Atg14 was dispensable for the latter. Serum cytokine analyses and genetic crosses further revealed distinct mechanisms contribute to the hypersensitivity of autophagy gene-deficient mice in these CSS models. Surprisingly, TNF was dispensable for the increased mortality of myeloid 5-deficient mice challenged with LPS. Tissue-specific ablation of Atg5 in cells expressing ITGAX/CD11c and LYZ2/LYSM, but not S100A8/MRP8, defined a myeloid subset that protected against TNF, while protection against LPS was conferred by Atg5 in a distinct subset of LYZ2-expressing cells. Together, this study identifies autophagy gene sets and specific cell types that protect against fatal inflammation due to CSS, highlighting important differences in two commonly used murine models of the disorder. ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BECN1: beclin 1, autophagy related; CASP1: caspase 1; CASP4/CASP11: caspase 4, apoptosis-related cysteine peptidase; CIM: conditionally immortalized macrophage; CLP: cecal ligation and puncture; CSS: cytokine storm syndrome; DC: dendritic cell; IFNG/IFNγ: interferon gamma; IFNGR1: interferon gamma receptor 1; ip: intraperitoneal; iv: intravenous; IL12/p70: interleukin 12, p70 heterodimer; IL18: Interleukin 18; ITGAX/CD11c: integrin alpha X; LAP: LC3-associated phagocytosis; LPS: lipopolysaccharide; LYZ2/LYSM: lysozyme 2; MAP1LC3A/LC3: microtubule-associated protein 1 light chain 3 alpha; RB1CC1/FIP200: RB1-inducible coiled-coil 1; S100A8/MRP8: S100 calcium binding protein A8 (calgranulin A); TICAM1/TRIF: TIR domain containing adaptor molecule 1; TLR4: toll-like receptor 4; TNF: tumor necrosis factor.

Rift Valley Fever Virus (RVFV) is a zoonotic pathogen with pandemic potential. RVFV entry is mediated by the viral glycoprotein (Gn), but host entry factors remain poorly defined. Our genome-wide CRISPR screen identified low-density lipoprotein receptor-related protein 1 (mouse Lrp1/human LRP1), heat shock protein (Grp94), and receptor associated protein (RAP) as critical host factors for RVFV infection. RVFV Gn directly binds to specific clusters Lrp1 and is glycosylation independent. Exogenous addition of murine RAP domain 3 (mRAP(D3)) and anti-Lrp1 antibodies neutralize RVFV infection in taxonomically diverse cell lines. Mice treated with mRAP(D3) and infected with pathogenic RVFV are protected from disease and death. A mutant mRAPD3 that binds Lrp1 weakly failed to protect from RVFV infection. Altogether, these data support Lrp1 as a host entry factor for RVFV infection and defines a new target to limit RVFV infections.

Genes required for the lysosomal degradation pathway of autophagy play key roles in topologically distinct cellular processes with significant physiologic importance. One of the first-described of these ATG gene-dependent processes is the requirement for a subset of ATG genes in interferon-{gamma} (IFN{gamma})-induced inhibition of norovirus and Toxoplasma gondii replication. Herein we identified new genes that are required for or that negatively regulate this immune mechanism. Enzymes involved in the conjugation of UFM1 to target proteins including UFC1 and UBA5, negatively regulated IFN{gamma}-induced inhibition of norovirus replication via effects of Ern1. IFN{gamma}-induced inhibition of norovirus replication required Wipi2b and Atg9a, but not Becn1 (encoding Beclin1), Atg14, or Sqstm1. The phosphatidylinositol-3-phosphate and ATG16L1 binding domains of WIPI2B were required for IFN{gamma}-induced inhibition of norovirus replication. Both WIPI2 and SQSTM1 were required for IFN{gamma}-induced inhibition of Toxoplasma gondii replication in HeLa cells. These studies further delineate the mechanisms of a programmable form of cytokine-induced intracellular immunity that relies on an expanding cassette of essential ATG genes to restrict the growth of phylogenetically diverse pathogens. ImportanceInterferon-{gamma} is a critical mediator of cell-intrinsic immunity to intracellular pathogens. Understanding the complex cellular mechanisms supporting robust interferon-{gamma}-induced host defenses could aid in developing new therapeutics to treat infections. Here, we examined the impact of autophagy in the interferon-{gamma} induced host response. We demonstrate that CRISPR-Cas9 screens specifically targeting the autophagy pathway uncover a role for WIPI2 in IFN{gamma}-induced inhibition of Norovirus replication in mouse cells and IFN{gamma} mediated restriction of the Toxoplasma gondii parasitophorous vacuole in human cells. Furthermore, we found perturbation of UFMylation pathway components led to more robust IFN{gamma}-induced inhibition of Norovirus due to ER stress in vitro. Enhancing or inhibiting these dynamic cellular components could serve as a strategy to weaken intracellular pathogens and maintain an effective immune response.

Macrophages activated with interferon-γ (IFN-γ) in combination with other proinflammatory stimuli, such as lipopolysaccharide or tumor necrosis factor-α (TNF-α), respond with transcriptional and cellular changes that enhance clearance of intracellular pathogens at the risk of damaging tissues. IFN-γ effects must therefore be carefully balanced with inhibitory mechanisms to prevent immunopathology. We performed a genome-wide CRISPR knockout screen in a macrophage cell line to identify negative regulators of IFN-γ responses. We discovered an unexpected role of the ubiquitin-fold modifier (Ufm1) conjugation system (herein UFMylation) in inhibiting responses to IFN-γ and lipopolysaccharide. Enhanced IFN-γ activation in UFMylation-deficient cells resulted in increased transcriptional responses to IFN-γ in a manner dependent on endoplasmic reticulum stress responses involving Ern1 and Xbp1. Furthermore, UFMylation in myeloid cells is required for resistance to influenza infection in mice, indicating that this pathway modulates in vivo responses to infection. These findings provide a genetic roadmap for the regulation of responses to a key mediator of cellular immunity and identify a molecular link between the UFMylation pathway and immune responses.

An unbridled host immune response to SARS-CoV-2 infection likely underlies severe cases of the disease and has been labeled a “Cytokine Storm Syndrome”. We emphasize that categorization of syndromes triggered by a completely novel pathogen based on other seemingly similar, but potentially distinct, known entities is an inherently risky endeavor., Highlights • An uncontrolled host immune response following SARS-CoV-2 infection and a cytokine storm contribute to severe COVID-19. • Among the myriad clinical syndromes identified in COVID-19 patients, Multisystem Inflammatory Syndrome in Children (MIS-C) is emerging as a severe complication in pediatric patients. • Cohorts of pediatric patients with MIS-C reveal overlapping but distinct pictures from SARS-CoV-2 associated Cytokine Storm Syndrome with respect to their clinical and laboratory profile. • While candidates for targeted therapies based on understanding of the pathogenesis of SARS-CoV-2-associated Cytokine Storm Syndromes are emerging, and there may be overlap in the pathogenesis and therapy, it is clear that syndrome-specific approaches will be necessary.

Summary Recent studies suggest that mitochondria can be transferred between cells to support the survival of metabolically compromised cells. However, whether intercellular mitochondria transfer occurs in white adipose tissue (WAT) or regulates metabolic homeostasis in vivo remains unknown. We found that macrophages acquire mitochondria from neighboring adipocytes in vivo and that this process defines a transcriptionally distinct macrophage subpopulation. A genome-wide CRISPR-Cas9 knockout screen revealed that mitochondria uptake depends on heparan sulfates (HS). High-fat diet (HFD)-induced obese mice exhibit lower HS levels on WAT macrophages and decreased intercellular mitochondria transfer from adipocytes to macrophages. Deletion of the HS biosynthetic gene Ext1 in myeloid cells decreases mitochondria uptake by WAT macrophages, increases WAT mass, lowers energy expenditure, and exacerbates HFD-induced obesity in vivo. Collectively, this study suggests that adipocytes and macrophages employ intercellular mitochondria transfer as a mechanism of immunometabolic crosstalk that regulates metabolic homeostasis and is impaired in obesity.

Mutations in the autophagy gene EPG5 are responsible for Vici syndrome, a multisystem human genetic disease with a combined immunodeficiency component. However, the mechanism(s) by which EPG5 regulates immune signaling are incompletely understood. Previously, we found that Epg5−/− mice are resistant to influenza and exhibit hyperinflammation in the lungs including elevated IL1B/IL-1β and TNF/TNFa. Here, we show that the disruption of Epg5 results in protection against multiple enteric viruses including norovirus and rotavirus. RNA sequencing revealed that IFN-λ responses are highly upregulated in the intestines of Epg5−/− mice. Further, mice lacking Epg5 exhibit substantial alterations of the intestinal microbiota. Surprisingly, germ-free Epg5−/− mice showed persistent inflammation of both the intestine and lung, suggesting a microbiota independent mechanism. Epg5−/−Ifnlr1−/− mice, which lack the receptor for IFN-λ, regained susceptibility to viral infection but maintained microbial dysbiosis, indicating that IFN-λ signaling is the primary mediator of resistance to enteric viruses but is dispensable for microbial dysbiosis in Epg5−/− mice. Intriguingly, epg-5-mutant Caenorhabditis elegans animals are also resistant to Orsay virus, which is an intestinal cell-tropic virus and the only known virus that naturally infects C. elegans. This study unveils an important role for autophagy gene Epg5 in protection of mammalian hosts by modulating intestinal IFN-λ responses, which is unexpectedly independent of the microbiota, and raises the possibility of a conserved viral resistance mechanism that is shared between C. elegans and mammals.

Host inflammatory responses must be tightly regulated to ensure effective immunity while limiting tissue injury. IFN gamma (IFNγ) primes macrophages to mount robust inflammatory responses. However, IFNγ also induces cell death, and the pathways that regulate IFNγ-induced cell death are incompletely understood. Using genome-wide CRISPR/Cas9 screening, we identified autophagy genes as central mediators of myeloid cell survival during the IFNγ response. Hypersensitivity of autophagy gene-deficient cells to IFNγ was mediated by tumor necrosis factor (TNF) signaling via receptor interacting protein kinase 1 (RIPK1)- and caspase 8-mediated cell death. Mice with myeloid cell-specific autophagy gene deficiency exhibited marked hypersensitivity to fatal systemic TNF administration. This increased mortality in myeloid autophagy gene-deficient mice required the IFNγ receptor, and mortality was completely reversed by pharmacologic inhibition of RIPK1 kinase activity. These findings provide insight into the mechanism of IFNγ-induced cell death via TNF, demonstrate a critical function of autophagy genes in promoting cell viability in the presence of inflammatory cytokines, and implicate this cell survival function in protection against mortality during the systemic inflammatory response.

Convection is the predominant mechanism by which energy and angular momentum are transported in the outer portion of the Sun. The resulting overturning motions are also the primary energy source for the solar magnetic field. An accurate solar dynamo model therefore requires a complete description of the convective motions, but these motions remain poorly understood. Studying stellar convection numerically remains challenging; it occurs within a parameter regime that is extreme by computational standards. The fluid properties of the convection zone are characterized in part by the Prandtl number $\mathrm{Pr}=\nu/\kappa$, where $\nu$ is the kinematic viscosity and $\kappa$ is the thermal diffusion; in stars, $\mathrm{Pr}$ is extremely low, $\mathrm{Pr}\approx 10^{-7}$. The influence of $\mathrm{Pr}$ on the convective motions at the heart of the dynamo is not well understood since most numerical studies are limited to using $\mathrm{Pr}\approx1$. We systematically vary $\mathrm{Pr}$ and the degree of thermal forcing, characterized through a Rayleigh number, to explore its influence on the convective dynamics. For sufficiently large thermal driving, the simulations reach a so-called convective free-fall state where diffusion no longer plays an important role in the interior dynamics. Simulations with a lower $\mathrm{Pr}$ generate faster convective flows and broader ranges of scales for equivalent levels of thermal forcing. Characteristics of the spectral distribution of the velocity remain largely insensitive to changes in $\mathrm{Pr}$. Importantly, we find that $\mathrm{Pr}$ plays a key role in determining when the free-fall regime is reached by controlling the thickness of the thermal boundary layer.

Summary Cellular tropism during persistent viral infection is commonly conferred by the interaction of a viral surface protein with a host receptor complex. Norovirus, the leading global cause of gastroenteritis, can be persistently shed during infection, but its in vivo cellular tropism and tropism determinants remain unidentified. Using murine norovirus (MNoV), we determine that a small number of intestinal epithelial cells (IECs) serve as the reservoir for fecal shedding and persistence. The viral non-structural protein NS1, rather than a viral surface protein, determines IEC tropism. Expression of NS1 from a persistent MNoV strain is sufficient for an acute MNoV strain to target IECs and persist. In addition, interferon-lambda (IFN-λ) is a key host determinant blocking MNoV infection in IECs. The inability of acute MNoV to shed and persist is rescued in Ifnlr1 −/− mice, suggesting that NS1 evades IFN-λ-mediated antiviral immunity. Thus, NS1 and IFN-λ interactions govern IEC tropism and persistence of MNoV.

Background The largest known outbreak of enterovirus D68 (EV-D68) infections occurred during 2014. The goal of our study is to characterize the illness severity and clinical presentation of children infected with EV-D68 in comparison to non-EV-D68-human rhinoviruses/enteroviruses (HRV/EV). Method Our study is a retrospective analysis of severity level, charges and length of stay of children who presented to St. Louis Children's Hospital from August 8, 2014 to October 31, 2014 and tested positive for EV-D68 in comparison to non-EV-D68-HRV/EV-infected patients. Chart review was performed for all EV-D68-infected patients and age and severity matched non-EV-D68-HRV/EV-infected patients. Result There was a striking increase in hospital census in August of 2014 in our hospital with simultaneous increase in the number of patients with EV-D68 infection. There was no significant difference in severity of illness, length of stay or total charges between EV-D68-infected and non-EV-D68-HRV/EV-infected children. EV-D68 infection was characterized by presenting complaints of difficulty breathing (80%) and wheezing (67%) and by findings of tachypnea (65%), wheezing (71%) and retractions (65%) on examination. The most common interventions were albuterol (79%) and corticosteroid (68%) treatments, and the most common discharge diagnosis was asthma exacerbation (55%). Conclusion EV-D68 caused a significant outbreak in 2014 with increased hospital admissions and associated increased charges. There was no significant difference in severity of illness caused by EV-D68 compared with non-EV-D68-HRV/EV infections suggesting that the impact from EV-D68 was because of increased number of infected children presenting to the hospital and not necessarily due to increased severity of illness.

Selective autophagy involves the recognition and targeting of specific cargo, such as damaged organelles, misfolded proteins, or invading pathogens for lysosomal destruction1,2,3,4. Yeast genetic screens have identified proteins required for different forms of selective autophagy, including cytoplasm-to-vacuole targeting, pexophagy and mitophagy, and mammalian genetic screens have identified proteins required for autophagy regulation5. However, there have been no systematic approaches to identify molecular determinants of selective autophagy in mammalian cells. Here, to identify mammalian genes required for selective autophagy, we performed a high-content, image-based, genome-wide small interfering RNA screen to detect genes required for the colocalization of Sindbis virus capsid protein with autophagolysosomes. We identified 141 candidate genes required for viral autophagy, which were enriched for cellular pathways related to messenger RNA processing, interferon signalling, vesicle trafficking, cytoskeletal motor function and metabolism. Ninety-six of these genes were also required for Parkin-mediated mitophagy, indicating that common molecular determinants may be involved in autophagic targeting of viral nucleocapsids and autophagic targeting of damaged mitochondria. Murine embryonic fibroblasts lacking one of these gene products, the C2-domain containing protein, SMURF1, are deficient in the autophagosomal targeting of Sindbis and herpes simplex viruses and in the clearance of damaged mitochondria. Moreover, SMURF1-deficient mice accumulate damaged mitochondria in the heart, brain and liver. Thus, our study identifies candidate determinants of selective autophagy, and defines SMURF1 as a newly recognized mediator of both viral autophagy and mitophagy.