The olfactory receptor Olfr78 promotes differentiation of enterochromaffin cells in the mouse colon.

The gastrointestinal epithelium constitutes a chemosensory system for microbiota-derived metabolites such as short-chain fatty acids (SCFA). Here, we investigate the spatial distribution of Olfr78, one of the SCFA receptors, in the mouse intestine and study the transcriptome of colon enteroendocrine cells expressing Olfr78. The receptor is predominantly detected in the enterochromaffin and L subtypes in the proximal and distal colon, respectively. Using the Olfr78-GFP and VilCre/Olfr78flox transgenic mouse lines, we show that loss of epithelial Olfr78 results in impaired enterochromaffin cell differentiation, blocking cells in an undefined secretory lineage state. This is accompanied by a reduced defense response to bacteria in colon crypts and slight dysbiosis. Using organoid cultures, we further show that maintenance of enterochromaffin cells involves activation of the Olfr78 receptor via the SCFA ligand acetate. Taken together, our work provides evidence that Olfr78 contributes to colon homeostasis by promoting enterochromaffin cell differentiation.

Diamond-Blackfan anemia, the archetype of ribosomopathy: How distinct is it from the other constitutional ribosomopathies?

Diamond-Blackfan anemia (DBA) was the first ribosomopathy described in humans. DBA is a congenital hypoplastic anemia, characterized by macrocytic aregenerative anemia, manifesting by differentiation blockage between the BFU-e/CFU-e developmental erythroid progenitor stages. In 50 % of the DBA cases, various malformations are noted. Strikingly, for a hematological disease with a relative erythroid tropism, DBA is due to ribosomal haploinsufficiency in 24 different ribosomal protein (RP) genes. A few other genes have been described in DBA-like disorders, but they do not fit into the classical DBA phenotype (Sankaran et al., 2012; van Dooijeweert et al., 2022; Toki et al., 2018; Kim et al., 2017 [1-4]). Haploinsufficiency in a RP gene leads to defective ribosomal RNA (rRNA) maturation, which is a hallmark of DBA. However, the mechanistic understandings of the erythroid tropism defect in DBA are still to be fully defined. Erythroid defect in DBA has been recently been linked in a non-exclusive manner to a number of mechanisms that include: 1) a defect in translation, in particular for the GATA1 erythroid gene; 2) a deficit of HSP70, the GATA1 chaperone, and 3) free heme toxicity. In addition, p53 activation in response to ribosomal stress is involved in DBA pathophysiology. The DBA phenotype may thus result from the combined contributions of various actors, which may explain the heterogenous phenotypes observed in DBA patients, even within the same family.

Potential efficacy of T and B lymphocyte-targeted therapies on articular involvement of patients with rheumatoid arthritis and systemic sclerosis overlap syndrome. Results from a 2-centre series of 22 cases.

OBJECTIVES: To analyse in routine practice the efficacy of targeted therapies on joint involvement of patients with rheumatoid arthritis/systemic sclerosis (RA/SSc) overlap syndrome. METHODS: This was a retrospective analysis of medical records of two academic centres over a 10-year period. Joint response to targeted therapies was measured according to EULAR criteria based on Disease Activity Score (DAS)-28. In addition, changes in CRP level and glucocorticoid consumption were recorded. RESULTS: Nineteen patients were included. Methotrexate (n=11) and hydroxychloroquine (n=4) were the most used first-line treatments. Targeted therapies were frequently used (n=14). Tocilizumab was the most selected therapy (n=8), then rituximab (n=5), abatacept and anti-tumour necrosis factor (n=4). Twenty-one treatment sequences were assessed, including 18 with EULAR response criteria. Responses were "good" or "moderate" in 100% (4/4) of patients treated with abatacept, 80% (4/5) with rituximab, 40% (2/5) with tocilizumab, and 25% (1/4) with anti-TNF. T and B lymphocyte-targeted therapies (abatacept, rituximab) resulted more frequently in a "good" or "moderate" response compared to cytokine inhibitors (tocilizumab, etanercept, infliximab) with a significant decrease in DAS-28 at 6 months (-1.75; p=0.016) and a trend to a lower consumption of glucocorticoids. CCONCLUSIONS: In patients with RA/SSc overlap syndrome refractory to conventional synthetic-DMARDs, T and B lymphocyte-targeted therapies seem to be a promising therapeutic option to control joint activity.

IL-6 enhances CD4 cell motility by sustaining mitochondrial Ca2+ through the noncanonical STAT3 pathway.

Interleukin 6 (IL-6) is known to regulate the CD4 T cell function by inducing gene expression of a number of cytokines through activation of Stat3 transcription factor. Here, we reveal that IL-6 strengthens the mechanics of CD4 T cells. The presence of IL-6 during activation of mouse and human CD4 T cells enhances their motility (random walk and exploratory spread), resulting in an increase in travel distance and higher velocity. This is an intrinsic effect of IL-6 on CD4 T-cell fitness that involves an increase in mitochondrial Ca2+ Although Stat3 transcriptional activity is dispensable for this process, IL-6 uses mitochondrial Stat3 to enhance mitochondrial Ca2+-mediated motility of CD4 T cells. Thus, through a noncanonical pathway, IL-6 can improve competitive fitness of CD4 T cells by facilitating cell motility. These results could lead to alternative therapeutic strategies for inflammatory diseases in which IL-6 plays a pathogenic role.

Interleukin-6 is an activator of pituitary stem cells upon local damage, a competence quenched in the aging gland.

Stem cells in the adult pituitary are quiescent yet show acute activation upon tissue injury. The molecular mechanisms underlying this reaction are completely unknown. We applied single-cell transcriptomics to start unraveling the acute pituitary stem cell activation process as occurring upon targeted endocrine cell-ablation damage. This stem cell reaction was contrasted with the aging (middle-aged) pituitary, known to have lost damage-repair capacity. Stem cells in the aging pituitary show regressed proliferative activation upon injury and diminished in vitro organoid formation. Single-cell RNA sequencing uncovered interleukin-6 (IL-6) as being up-regulated upon damage, however only in young but not aging pituitary. Administering IL-6 to young mice promptly triggered pituitary stem cell proliferation, while blocking IL-6 or associated signaling pathways inhibited such reaction to damage. By contrast, IL-6 did not generate a pituitary stem cell activation response in aging mice, coinciding with elevated basal IL-6 levels and raised inflammatory state in the aging gland (inflammaging). Intriguingly, in vitro stem cell activation by IL-6 was discerned in organoid culture not only from young but also from aging pituitary, indicating that the aging gland's stem cells retain intrinsic activatability in vivo, likely impeded by the prevailing inflammatory tissue milieu. Importantly, IL-6 supplementation strongly enhanced the growth capability of pituitary stem cell organoids, thereby expanding their potential as an experimental model. Our study identifies IL-6 as a pituitary stem cell activator upon local damage, a competence quenched at aging, concomitant with raised IL-6/inflammatory levels in the older gland. These insights may open the way to interfering with pituitary aging.

Stroma AReactive Invasion Front Areas (SARIFA) - a new prognostic biomarker in gastric cancer related to tumor-promoting adipocytes.

Compared to other malignancies, there is a lack of easy-to-evaluate biomarkers for gastric cancer, which is associated with an adverse clinical outcome in many cases. Here, we present Stroma AReactive Invasion Front Areas (SARIFA) as a new histological prognostic marker. We defined SARIFA as the direct contact between a cluster of tumor glands/cells comprising at least five tumor cells and inconspicuous surrounding adipose tissue at the invasion front. A total of 480 adenocarcinomas of the stomach and the gastroesophageal junction from two different collections were classified according to SARIFA. To understand the potential underlying mechanisms, a transcriptome analysis was conducted using digital spatial profiling (DSP). It was found that 20% of the tumors were SARIFA-positive. Kappa values between the three pathologists were good in both collections: 0.74 and 0.78. Patients who presented SARIFA-positive tumors had a significantly lower overall survival in Collections A (median: 20.0 versus 44.0 months; p = 0.014, n = 160) and B (median: 15.0 versus 41.0 months; p < 0.0001, n = 320). SARIFA positivity emerged as a negative independent prognostic factor for overall survival (HR 1.638, 95% CI 1.153-2.326, p = 0.006). Using DSP, the most upregulated genes in SARIFA-positive cases were those associated with triglyceride catabolism and endogenous sterols. COL15A1, FABP2, and FABP4 were differentially expressed in positive cases. At the protein level, the expression of proteins related to lipid metabolism was confirmed. SARIFA combines low inter-observer variability, minimal effort, and high prognostic relevance, and is therefore an extremely promising biomarker related to tumor-promoting adipocytes in gastric cancer. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

[Sperm donation in Switzerland]. / Don de sperme en Suisse.

The acceptance of "marriage for all" in Switzerland has enabled married couples to have access to medically assisted reproduction (MAR) through sperm donation from July 2022. We present the Swiss legal context of sperm donation, the different techniques, the selection of donors and the method of attribution to recipient couples. This article also describes the complexities of managing a sperm bank in Switzerland, presents some of the figures associated and address the fundamental question of access to origins and the secrecy that may be linked to sperm donation.

L'acceptation du « mariage pour tous ¼ en Suisse a permis aux couples de femmes mariées d'avoir accès à la procréation médicalement assistée (PMA) par don de sperme dès juillet 2022. Nous présentons le contexte légal de la pratique du don de sperme en Suisse, les différentes techniques, la sélection des donneurs et le mode d'attribution aux couples receveurs. Cet article décrit également la complexité de la gestion d'une banque de sperme en Suisse, présente quelques chiffres liés à cette activité et aborde également la question fondamentale de l'accès aux origines et du secret qui peut être lié au don de sperme.

Survival, cost and added therapeutic benefit of drugs granted early access through the French temporary authorization for use program in solid tumors from 2009 to 2019.

Decisions on market authorization (MA) and reimbursement have different durations across countries because of health technology assessment (HTA) procedures and negotiations between manufacturers and national authorities. To overcome this delay, France has implemented a Temporary Authorization for Use (ATU) program that allows early access to drugs before MA, in order to treat patients with unmet medical needs. The objectives of our study were to establish the added therapeutic benefit (ATB) of ATUs for solid tumors and to investigate the correlations between three tools evaluating ATB and survival outcomes and drug costs. Data on ATUs granted from January 2009 to December 2019 to treat solid tumors were analyzed. An assessment of their ATB was conducted using the American Society of Clinical Oncology-Value Framework (ASCO-VF), the European Society for Medical Oncology-Magnitude Clinical Benefit Scale (ESMO-MCBS) and the French HTA criterion, clinical added value (CAV). The latter score determines reimbursement and national market access. Thirty-five drugs in 39 indications were granted ATUs. All of them obtained MA and derived a clinical benefit to be reimbursed by the Social Security. Twenty-eight (71.8%) had CAV compared to preexisting therapies. 24/38 (63.2%) had a 4-5 ESMO-MCBS score and 19/33 (57.6%) had an ASCO-VF score over 45. No correlations were found between cost, PFS, OS, CAV and ASCO-VF score, while high ESMO-MCBS scores were correlated to OS. In conclusion, many patients were treated with innovations before MA thanks to ATU, although there are discrepancies between ATB scales, hence the importance of international collaboration in the evaluation of innovative therapies.

An Immunological Axis Involving Interleukin 1ß and Leucine-Rich-α2-Glycoprotein Reflects Therapeutic Response of Children with Kawasaki Disease: Implications from the KAWAKINRA Trial.

PURPOSE: A recent phase II open-label study of the interleukin 1 (IL-1) receptor antagonist (IL-1Ra) anakinra in treating IVIG-resistant Kawasaki disease (KD) patients reported promising results. Here, we aimed to characterize the immunological impact of IL-1 blockade in this unique study population. METHODS: Patients' and control sera and supernatants of cells (whole blood, neutrophils, coronary artery endothelial cells) stimulated with recombinant IL-1ß were analyzed for single or multiple marker (n = 22) expression by ELISA or multiplexed bead array assay. Data were analyzed using unsupervised hierarchical clustering, multiple correlation, and multi-comparison statistics and were compared to retrospective analyses of KD transcriptomics. RESULTS: Inflammation in IVIG-resistant KD (n = 16) is hallmarked by over-expression of innate immune mediators (particularly IL-6 > CXCL10 > S100A12 > IL-1Ra). Those as well as levels of immune or endothelial cell activation markers (sICAM-1, sVCAM-1) declined most significantly in course of anakinra treatment. Prior as well as following IL-1R blockade, over-expression of leucine-rich-α2-glycoprotein 1 (LRG1) associated best with remnant inflammatory activity and the necessity to escalate anakinra dosage and separated inflammatory KD patients from sJIA-MAS (n = 13) and MIS-C (n = 4). Protein as well as retrospective gene expression analyses indicated tight association of LRG1 with IL-1ß signaling and neutrophilia, while particularly neutrophil stimulation with recombinant IL-1ß resulted in concentration-dependent LRG1 release. CONCLUSION: Our study identifies LRG1 as known trigger of endothelial activation and cardiac re-modeling to associate with IL-1ß signaling in KD. Besides a potential patho-mechanistic implication of these findings, our data suggest blood leukocyte and neutrophil counts to best predict response to IL-1Ra treatment in IVIG-resistant KD.

LGR5 controls extracellular matrix production by stem cells in the developing intestine.

The Lgr5 receptor is a marker of intestinal stem cells (ISCs) that regulates Wnt/b-catenin signaling. In this study, phenotype analysis of knockin/knockout Lgr5-eGFP-IRES-Cre and Lgr5-DTReGFP embryos reveals that Lgr5 deficiency during Wnt-mediated cytodifferentiation results in amplification of ISCs and early differentiation into Paneth cells, which can be counteracted by in utero treatment with the Wnt inhibitor LGK974. Conditional ablation of Lgr5 postnatally, but not in adults, alters stem cell fate toward the Paneth lineage. Together, these in vivo studies suggest that Lgr5 is part of a feedback loop to adjust the Wnt tone in ISCs. Moreover, transcriptome analyses reveal that Lgr5 controls fetal ISC maturation associated with acquisition of a definitive stable epithelial phenotype, as well as the capacity of ISCs to generate their own extracellular matrix. Finally, using the ex vivo culture system, evidences are provided that Lgr5 antagonizes the Rspondin 2-Wnt-mediated response in ISCs in organoids, revealing a sophisticated regulatory process for Wnt signaling in ISCs.

Potential Benefit of Rituximab in Rhupus Patients From a Single-Center: A Series of 16 Cases.

BACKGROUND: Rhupus syndrome is better characterized, but uncertainties remain, and therapeutic management must be defined. The objective was to analyze therapeutic procedures with a focus on biologic disease-modifying antirheumatic drugs (bDMARDs). METHODS: This 10-year medical records review was based on diagnosis codes (rheumatoid arthritis [RA] and systemic lupus erythematosus [SLE]) and biological data (anti-CCP testing, anti-dsDNA, and anti-RNP antibodies). Patients fulfilling 2010 ACR/EULAR and 2012 SLICC and/or 2019 ACR/EULAR classification criteria for RA and SLE, respectively, were included. RESULTS: Sixteen patients were identified. Rheumatoid arthritis most often preceded rhupus, with predominant articular pattern; 11 of them had erosive arthropathy. Skin involvement was the most frequent associated manifestation (n = 12). Serious events were reported, including active glomerulonephritis (n = 3), ischemic stroke (n = 1), and myocardial infarction (n = 1). Immunological profiles showed positivity for antinuclear (n = 16), anti-dsDNA (n = 9), and anti-CCP (n = 9). Ten patients required bDMARDs. All types of RA-approved bDMARDs were used. Abatacept was considered effective in 3 of the 4 patients, with 1 primary failure, 1 secondary escape, and 2 therapeutic maintenances, whereas primary or secondary failure was observed under tocilizimub and TNF-blocking agents. Rituximab was the most prescribed (n = 9) and the most effective with a sustained response in 6 patients. CONCLUSIONS: In rhupus refractory to conventional treatment, T or B lymphocytes targeted therapies, and particularly rituximab, seem to be a relevant therapeutic option unlike anticytokine biologics.

Impact of pre-eclampsia on renal outcome in sickle cell disease patients.

The long-term consequences of pre-eclampsia (PrE) for renal function have never been determined in patients with sickle cell disease (SCD). Between 2008 and 2015, we screened 306 pregnancies in women with SCD and identified 40 with PrE (13%). The control group consisted of 65 pregnant SCD patients without PrE. In multivariable analysis, PrE events were associated with an increase of 1 log of lactate dehydrogenase level (adjusted odds ratio, aOR = 3·83, P = 0·05), a decrease of 10 g/l of haemoglobin levels (aOR = 2·48, P = 0·006) and one or more vaso-occlusive crisis during pregnancy (aOR = 16·68, P = 0·002). Estimated glomerular filtration rate (eGFR) was similar in the two groups at steady state but was significantly lower in the PrE group after one year of follow-up and at last follow-up (130 vs 148 ml/min/1·73 m2 , P < 0·001 and 120 vs 130 ml/min/1·73 m2 , P < 0·001, respectively). In multivariable analysis, eGFR had returned to steady-state levels one year after pregnancy in patients without PrE but continued to decrease in patients with PrE (ß = -18·15 ml/min/1·73 m2 , P < 0·001). This decline was more marked at the end of follow-up (ß = -31·15 ml/min, P < 0·001). In conclusion, PrE episodes are associated with a significant risk of subsequent renal function decline in SCD patients.

STATus report on tetramers.

STAT proteins bind DNA as dimers to regulate gene expression. Cooperative recruitment of pairs of dimers (tetramers) to adjacent DNA sites has also been documented. In this issue, Lin et al. (2012) examined tetramer function in vivo and showed that STAT5 tetramers function primarily as transcriptional activators.

Silver(I) Oxide-/DBU-Promoted Synthesis of Dihydrofuran Units through Allenyl Silver Formation.

A formal [3+2] cyclization mediated by silver(I) oxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is described herein. Through a broad variety of carbonyl compounds, this system can promote cyclization reactions with high yield (up to 85 %) and diastereoselectivity (up to 95:5) for a straightforward access to complex and congested dihydrofuran derivatives in one step under mild conditions. Based on DFT studies, the proposed mechanism would involve an allenyl silver intermediate.

The evolving blood donor deferral policy for men who have sex with men: impact on the risk of HIV transmission by transfusion in France.

BACKGROUND: Blood donation deferral for men who have sex with men (MSM) in France was reduced from permanent to 12 months in July 2016. To inform a further reduction of the deferral period, an HIV risk assessment was conducted with two scenarios: S1, 4-month deferral; S2, 4-month deferral only in the case of more than one sexual partner (i.e., similar to other blood donors). METHODS: Baseline HIV residual risk (RR) was calculated from July 2016 to December 2017, using the Incidence Rate-Window Period method. The impact of both scenarios on RR was assessed using data from surveys on MSM and blood donors, to estimate 1) the number of additional MSM expected to donate in each scenario and 2) HIV incidence among these donors. RESULTS: Baseline HIV RR was estimated at 1 in 6,380,000 donations. For S1, an additional 733 MSM donors, and an additional 0.09 HIV-positive donations were estimated, yielding an unchanged RR of 1 in 6,300,000. For S2, these numbers were estimated at 3102 and 3.92, respectively, yielding an RR of 1 in 4,300,000. Sensitivity analyses showed that, under worst-case assumptions, the RR would equal 1 in 6,225,000 donations for S1 and 1 in 3,000,000 for S2. CONCLUSION: For both scenarios, the HIV RR remains very low. For S1, the risk is identical to the baseline RR. For S2, it is 1.5 times higher, and sensitivity analysis shows that this estimate is less robust than for S1. The French Minister of Health announced that S1 will be implemented in April 2020.

Trop2 marks transient gastric fetal epithelium and adult regenerating cells after epithelial damage.

Mouse fetal intestinal progenitors lining the epithelium prior to villogenesis grow as spheroids when cultured ex vivo and express the transmembrane glycoprotein Trop2 as a marker. Here, we report the characterization of Trop2-expressing cells from fetal pre-glandular stomach, growing as immortal undifferentiated spheroids, and their relationship with gastric development and regeneration. Trop2(+) cells generating gastric spheroids differed from adult glandular Lgr5(+) stem cells, but appeared highly related to fetal intestinal spheroids. Although they shared a common spheroid signature, intestinal and gastric fetal spheroid-generating cells expressed organ-specific transcription factors and were committed to intestinal and glandular gastric differentiation, respectively. Trop2 expression was transient during glandular stomach development, being lost at the onset of gland formation, whereas it persisted in the squamous forestomach. Undetectable under homeostasis, Trop2 was strongly re-expressed in glands after acute Lgr5(+) stem cell ablation or following indomethacin-induced injury. These highly proliferative reactive adult Trop2(+) cells exhibited a transcriptome displaying similarity with that of gastric embryonic Trop2(+) cells, suggesting that epithelium regeneration in adult stomach glands involves the partial re-expression of a fetal genetic program.

Assembly of the Entire Carbon Backbone of a Stereoisomer of the Antitumor Marine Natural Product Hemicalide.

A strategy for the assembly of the entire carbon backbone of a stereoisomer of the antitumor marine natural product hemicalide has been investigated. The devised convergent approach relies on Horner-Wadsworth-Emmons and Julia-Kocienski olefination reactions for the construction of the C6=C7 and C34=C35 double bonds, respectively, an aldol reaction to create the C27-C28 bond, and a Suzuki-Miyaura cross-coupling as the endgame to form the C15-C16 bond.

Ti(II) and Rh(I) Complexes as Reagents toward a Thapsigargin Core.

A novel approach toward the [5-7]fused bicyclic core of thapsigargin, a subnanomolar inhibitor of the endo/sarcoplasmic calcium ATPase (SERCA), is presented. The synthetic route includes an original Ti(II)-mediated hydroxy-directed reductive coupling of an enantiomerically enriched propargylic alcohol and an intramolecular Rh(I)-catalyzed cyclocarbonylation reaction as key steps. Interestingly, through the first experiments of titanocene-mediated reductive cyclization of a 1,8-enyne, a seven-membered cycle was isolated as a unique product with a total diastereoselectivity.

The use and reporting of airline passenger data for infectious disease modelling: a systematic review.

BackgroundA variety of airline passenger data sources are used for modelling the international spread of infectious diseases. Questions exist regarding the suitability and validity of these sources.AimWe conducted a systematic review to identify the sources of airline passenger data used for these purposes and to assess validation of the data and reproducibility of the methodology.MethodsArticles matching our search criteria and describing a model of the international spread of human infectious disease, parameterised with airline passenger data, were identified. Information regarding type and source of airline passenger data used was collated and the studies' reproducibility assessed.ResultsWe identified 136 articles. The majority (n = 96) sourced data primarily used by the airline industry. Governmental data sources were used in 30 studies and data published by individual airports in four studies. Validation of passenger data was conducted in only seven studies. No study was found to be fully reproducible, although eight were partially reproducible.LimitationsBy limiting the articles to international spread, articles focussed on within-country transmission even if they used relevant data sources were excluded. Authors were not contacted to clarify their methods. Searches were limited to articles in PubMed, Web of Science and Scopus.ConclusionWe recommend greater efforts to assess validity and biases of airline passenger data used for modelling studies, particularly when model outputs are to inform national and international public health policies. We also recommend improving reporting standards and more detailed studies on biases in commercial and open-access data to assess their reproducibility.

PKR Transduces MDA5-Dependent Signals for Type I IFN Induction.

Sensing invading pathogens early in infection is critical for establishing host defense. Two cytosolic RIG-like RNA helicases, RIG-I and MDA5, are key to type I interferon (IFN) induction in response to viral infection. Mounting evidence suggests that another viral RNA sensor, protein kinase R (PKR), may also be critical for IFN induction during infection, although its exact contribution and mechanism of action are not completely understood. Using PKR-deficient cells, we found that PKR was required for type I IFN induction in response to infection by vaccinia virus lacking the PKR antagonist E3L (VVΔE3L), but not by Sendai virus or influenza A virus lacking the IFN-antagonist NS1 (FluΔNS1). IFN induction required the catalytic activity of PKR, but not the phosphorylation of its principal substrate, eIF2α, or the resulting inhibition of host translation. In the absence of PKR, IRF3 nuclear translocation was impaired in response to MDA5 activators, VVΔE3L and encephalomyocarditis virus, but not during infection with a RIG-I-activating virus. Interestingly, PKR interacted with both RIG-I and MDA5; however, PKR was only required for MDA5-mediated, but not RIG-I-mediated, IFN production. Using an artificially activated form of PKR, we showed that PKR activity alone was sufficient for IFN induction. This effect required MAVS and correlated with IRF3 activation, but no longer required MDA5. Nonetheless, PKR activation during viral infection was enhanced by MDA5, as virus-stimulated catalytic activity was impaired in MDA5-null cells. Taken together, our data describe a critical and non-redundant role for PKR following MDA5, but not RIG-I, activation to mediate MAVS-dependent induction of type I IFN through a kinase-dependent mechanism.