Chemokines and chemokine receptors during COVID-19 infection.

Chemokines are crucial inflammatory mediators needed during an immune response to clear pathogens. However, their excessive release is the main cause of hyperinflammation. In the recent COVID-19 outbreak, chemokines may be the direct cause of acute respiratory disease syndrome, a major complication leading to death in about 40% of severe cases. Several clinical investigations revealed that chemokines are directly involved in the different stages of SARS-CoV-2 infection. Here, we review the role of chemokines and their receptors in COVID-19 pathogenesis to better understand the disease immunopathology which may aid in developing possible therapeutic targets for the infection.

Comparison of the Antiviral Activity of Remdesivir, Chloroquine, and Interferon-ß as Single or Dual Agents Against the Human Beta-Coronavirus OC43.

The human beta-coronavirus strain, OC43, provides a useful model for testing the antiviral activity of various agents. We compared the activity of several antiviral drugs against OC43, including remdesivir, chloroquine, interferon (IFN)-ß, IFN-λ1, and IFN-λ4, in two distinct cell types: human colorectal carcinoma cell line (HCT-8 cells) and normal human bronchial epithelial (NHBE) cells. We also tested whether these agents mediate additive, synergistic, or antagonistic activity against OC43 infection when used in combination. When used as single agents, remdesivir exhibited stronger antiviral activity than chloroquine, and IFN-ß exhibited stronger activity than IFN-λ1 or IFN-λ4 against OC43 in both HCT-8 and NHBE cells. Anakinra (IL-1 inhibitor) and tocilizumab (IL-6 inhibitor) did not mediate any antiviral activity. The combination of IFN-ß plus chloroquine or remdesivir resulted in higher synergy scores and higher expression of IFN-stimulated genes than did IFN-ß alone. In contrast, the combination of remdesivir plus chloroquine resulted in an antagonistic interaction in NHBE cells. Our findings indicate that the combined use of IFN-ß plus remdesivir or chloroquine induces maximal antiviral activity against human coronavirus strain OC43 in primary human respiratory epithelial cells. Furthermore, our experimental OC43 virus infection model provides an excellent method for evaluating the biological activity of antiviral drugs.

Potential of green tea EGCG in neutralizing SARS-CoV-2 Omicron variant with greater tropism toward the upper respiratory tract.

Background: COVID-19 due to SARS-CoV-2 infection has had an enormous adverse impact on global public health. As the COVID-19 pandemic evolves, the WHO declared several variants of concern (VOCs), including Alpha, Beta, Gamma, Delta, and Omicron. Compared with earlier variants, Omicron, now a dominant lineage, exhibits characteristics of enhanced transmissibility, tropism shift toward the upper respiratory tract, and attenuated disease severity. The robust transmission of Omicron despite attenuated disease severity still poses a great challenge for pandemic control. Under this circumstance, its tropism shift may be utilized for discovering effective preventive approaches. Scope and approach: This review aims to estimate the potential of green tea epigallocatechin gallate (EGCG), the most potent antiviral catechin, in neutralizing SARS-CoV-2 Omicron variant, based on current knowledge concerning EGCG distribution in tissues and Omicron tropism. Key findings and conclusions: EGCG has a low bioavailability. Plasma EGCG levels are in the range of submicromolar concentrations following green tea drinking, or reach at most low µM concentrations after pharmacological intervention. Nonetheless, its levels in the upper respiratory tract could reach concentrations as high as tens or even hundreds of µM following green tea consumption or pharmacological intervention. An approach for delivering sufficiently high concentrations of EGCG in the pharynx has been developed. Convincing data have demonstrated that EGCG at tens to hundreds of µM can dramatically neutralize SARS-CoV-2 and effectively eliminate SARS-CoV-2-induced cytopathic effects and plaque formation. Thus, EGCG, which exhibits hyperaccumulation in the upper respiratory tract, deserves closer investigation as an antiviral in the current global battle against COVID-19, given Omicron's greater tropism toward the upper respiratory tract.

Norovirus 3C-Like protease antagonizes interferon-ß production by cleaving NEMO.

An epidemic owing to Norovirus (NoV) has recently been occurring worldwide. Severe cases of NoV can lead to patient death, resulting in significant public health problems. In the early stages of infection, antagonizing the production of host interferon (IFN) is an important strategy for viruses to establish infection. However, the relationship between NoV and interferon and its mechanism remains unclear. In this study, the 3C-like protease encoded by NoV was found to effectively suppress Sendai virus (SEV)-mediated IFN-ß production by cleaving the NF-κB essential modulator (NEMO). Glutamine 205 is the site of NoV3CLpro-mediated cleavage of NEMO and this cleavage suppresses the ability of NEMO to activate downstream IFN production. These findings demonstrate that NoV3CLpro-induced cleavage limits NEMO to the activation of type I IFN signaling. In summary, our findings indicate that NoV3CLpro is a new interferon antagonist, and enhances our understanding of the escape of innate immunity mediated by NoV3CLpro.

Impact of early interferon-ß treatment on the prognosis of patients with COVID-19 in the first wave: A post hoc analysis from a multicenter cohort.

BACKGROUND: Interferon-ß is an attractive drug for repurposing and use in the treatment of COVID-19, based on its in vitro antiviral activity and the encouraging results from clinical trials. The aim of this study was to analyze the impact of early interferon-ß treatment in patients admitted with COVID-19 during the first wave of the pandemic. METHODS: This post hoc analysis of a COVID-19@Spain multicenter cohort included 3808 consecutive adult patients hospitalized with COVID-19 from 1 January to 17 March 2020. The primary endpoint was 30-day all-cause mortality, and the main exposure of interest was subcutaneous administration of interferon-ß, defined as early if started ≤ 3 days from admission. Multivariate logistic and Cox regression analyses were conducted to identify the associations of different variables with receiving early interferon-ß therapy and to assess its impact on 30-day mortality. A propensity score was calculated and used to both control for confounders and perform a matched cohort analysis. RESULTS: Overall, 683 patients (17.9%) received early interferon-ß therapy. These patients were more severely ill. Adjusted HR for mortality with early interferon-ß was 1.03 (95% CI, 0.82-1.30) in the overall cohort, 0.96 (0.82-1.13) in the PS-matched subcohort, and 0.89 (0.60-1.32) when interferon-ß treatment was analyzed as a time-dependent variable. CONCLUSIONS: In this multicenter cohort of admitted COVID-19 patients, receiving early interferon-ß therapy after hospital admission did not show an association with lower mortality. Whether interferon-ß might be useful in the earlier stages of the disease or specific subgroups of patients requires further research.

Clinical efficacy and safety of interferon-ß-containing regimens in the treatment of patients with COVID-19: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: The aim of this systematic review and meta-analysis of randomized controlled trials(RCTs) was to investigate the efficacy of interferon (IFN)-ß-containing regimens in treating patients with COVID-19. METHODS: PubMed, Embase, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov were searched from inception to 17 July 2021. RCTs comparing the clinical efficacy and safety of IFN-ß-containing regimens (study group) to other antiviral treatment options or placebo (control group) in treating patients with COVID-19 were included. RESULTS: Eight RCTs were included. No significant difference in the 28-day all-cause mortality rate was observed between the study and control groups (OR, 0.74; 95% CI, 0.44-1.24; I2 = 51%). The study groups had a lower rate of intensive care unit (ICU) admissions than the control groups (OR 0.58, 95% CI 0.36-0.95; I2 = 0%). Furthermore, INF-ß was not associated with an increased risk of any adverse event (AE) or serious AE when compared with the control group. CONCLUSIONS: IFN-ß does not appear to provide an increased survival benefit in hospitalized patients with COVID-19 but may help reduce the risk of ICU admission. Moreover, IFN-ß is a safe agent for use in the treatment of COVID-19.

SARS-CoV-2 NSP12 Protein Is Not an Interferon-ß Antagonist.

The coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is bringing an unprecedented health crisis to the world. To date, our understanding of the interaction between SARS-CoV-2 and host innate immunity is still limited. Previous studies reported that SARS-CoV-2 nonstructural protein 12 (NSP12) was able to suppress interferon-ß (IFN-ß) activation in IFN-ß promoter luciferase reporter assays, which provided insights into the pathogenesis of COVID-19. In this study, we demonstrated that IFN-ß promoter-mediated luciferase activity was reduced during coexpression of NSP12. However, we could show NSP12 did not affect IRF3 or NF-κB activation. Moreover, IFN-ß production induced by Sendai virus (SeV) infection or other stimulus was not affected by NSP12 at mRNA or protein level. Additionally, the type I IFN signaling pathway was not affected by NSP12, as demonstrated by the expression of interferon-stimulated genes (ISGs). Further experiments revealed that different experiment systems, including protein tags and plasmid backbones, could affect the readouts of IFN-ß promoter luciferase assays. In conclusion, unlike as previously reported, our study showed SARS-CoV-2 NSP12 protein is not an IFN-ß antagonist. It also rings the alarm on the general usage of luciferase reporter assays in studying SARS-CoV-2. IMPORTANCE Previous studies investigated the interaction between SARS-CoV-2 viral proteins and interferon signaling and proposed that several SARS-CoV-2 viral proteins, including NSP12, could suppress IFN-ß activation. However, most of these results were generated from IFN-ß promoter luciferase reporter assay and have not been validated functionally. In our study, we found that, although NSP12 could suppress IFN-ß promoter luciferase activity, it showed no inhibitory effect on IFN-ß production or its downstream signaling. Further study revealed that contradictory results could be generated from different experiment systems. On one hand, we demonstrated that SARS-CoV-2 NSP12 could not suppress IFN-ß signaling. On the other hand, our study suggests that caution needs to be taken with the interpretation of SARS-CoV-2-related luciferase assays.

An investigation into the beneficial effects of high-dose interferon beta 1-a, compared to low-dose interferon beta 1-a in severe COVID-19: The COVIFERON II randomized controlled trial.

INTRODUCTION: Coronavirus disease 2019 (COVID-19) has been a serious obstacle in front of public health. Interferon-beta 1a (IFN-ß 1a) has been used to treat patients with COVID-19. We aimed to compare the effectiveness of high-dose IFN-ß 1a compared to low dose IFN-ß 1a in severe COVID-19 cases. METHODS: In this randomized, controlled, and clinical trial, eligible patients with confirmed SARS-CoV-2 infections were randomly assigned to receive one of the two following therapeutic regimens: The intervention group was treated with high-dose IFN-ß 1a (Recigen) (Subcutaneous injections of 88 µg (24 million IU) on days 1, 3, 6) + lopinavir /ritonavir (Kaletra) (400 mg/100 mg twice a day for 10 days, orally) and the control group was treated with low-dose IFN-ß 1a (Recigen) (Subcutaneous injections of 44 µg (12 million IU) on days 1, 3, 6) + lopinavir /ritonavir (Kaletra) (400 mg/100 mg twice a day for 10 days, orally). RESULT: A total of 168 COVID- 19 confirmed patients underwent randomization; 83 were assigned to the intervention group and 85 were assigned to the control group. Median Time To Clinical Improvement (TTIC) for cases treated with low-dose IFN-ß1a was shorter than that for cases treated with high-dose IFN-ß1a (6 vs 10 days; P = 0.018). The mortality rates in intervention and control group were 41% and 36.5%, respectively. CONCLUSION: The use of high-dose IFN-ß 1a did not improve TTCI in hospitalized patients with moderate to severe COVID-19. Also, it did not have any significant effect on mortality reduction compared with treating with low-dose IFN-ß 1a. TRIAL REGISTRATION: This trial has been registered as ClinicalTrials.gov, NCT04521400.

Interferon-beta offers promising avenues to COVID-19 treatment: a systematic review and meta-analysis of clinical trial studies.

Severe acute respiratory syndrome coronavirus 2 principally weakens the hosts' innate immune system by impairing the interferon function and production. Type I interferons (IFNs) especially IFN-ß are best known for their antiviral activities. IFNs accompanied by the standard care protocols have opened up unique opportunities for treating the coronavirus disease 2019 (COVID-19). The databases including PubMed, SCOPUS, EMBASE, and Google Scholar were searched up to October 30, 2020. The primary and secondary outcomes were considered discharge and mortality, respectively. The abovementioned outcomes of standard care protocol were compared with the standard care plus IFN-ß in the confirmed COVID-19 patients. Out of 356 records identified, 12 randomized clinical trial studies were selected for full-text screening. Finally, 5 papers were included in the systematic review and 3 papers in the meta-analysis. The average mortality rate was reported as 6.195% and 18.02% in intervention and control groups, respectively. Likewise, the median days of hospitalization were lower in the intervention group (9 days) than the control group (12.25 days). According to meta-analysis, IFN-ß was found to increase the overall discharge rate (RR = 3.05; 95% CI: 1.09-5.01). Our findings revealed that early administration of IFN-ß in combination with antiviral drugs is a promising therapeutic strategy against COVID-19.

An investigation into the beneficial effects of high-dose interferon beta 1-a, compared to low-dose interferon beta 1-a (the base therapeutic regimen) in moderate to severe COVID-19: A structured summary of a study protocol for a randomized controlled l trial.

OBJECTIVES: We will investigate the effectiveness of high dose Interferon Beta 1a, compared to low dose Interferon Beta 1a (the base therapeutic regimen) in COVID-19 Confirmed Cases (Either RT-PCR or CT Scan Confirmed) with moderate to severe disease TRIAL DESIGN: This is a single center, open label, randomized, controlled, 2-arm parallel group (1:1 ratio), clinical trial. PARTICIPANTS: The eligibility criteria in this study is: age ≥ 18 years, oxygen saturation (SPO2) ≤ 93% or respiratory rate ≥ 24, at least one of the following manifestation: radiation contactless body temperature ≥37.8, Cough, shortness of breath, nasal congestion/ discharge, myalgia/arthralgia, diarrhea/vomiting, headache or fatigue on admission. The onset of the symptoms should be acute (≤ 14 days). The exclusion criteria include refusal to participate, using drugs with potential interaction with lopinavir/ritonavir or interferon-ß 1a, blood ALT/AST levels > 5 times the upper limit of normal on laboratory results, pregnant or lactating women, history of alcohol or drug addiction in the past 5 years, the patients who be intubated less than one hours after admission to hospital. This study will be undertaken at the Loghman Hakim Hospital, Shahid Beheshti University of Medical Sciences. INTERVENTION AND COMPARATOR: COVID- 19 confirmed patients (using the RT-PCR test or CT scan) will be randomly assigned to one of two groups. The intervention group (Arms1) will be treated with lopinavir / ritonavir (Kaletra) + high dose Interferon-ß 1a (Recigen) and the control group will be treated with lopinavir / ritonavir (Kaletra) + low dose Interferon-ß 1a (Recigen) (the base therapeutic regimen). Both groups will receive standard care consisting of the necessary oxygen support, non-invasive, or invasive mechanical ventilation. MAIN OUTCOMES: Primary outcome: Time to clinical improvement is our primary outcome measure. This is an improvement of two points on a seven-category ordinal scale (recommended by the World Health Organization: Coronavirus disease (COVID-2019) R&D. Geneva: World Health Organization) or discharge from the hospital, whichever comes first. SECONDARY OUTCOMES: mortality from the date of randomization until the last day of the study which will be the day all of the patients have had at least one of the following outcomes: 1) Improvement of two points on a seven-category ordinal scale. 2) Discharge from the hospital 3) Death. Improvement of SPO2 during the hospitalization, duration of hospitalization from date of randomization until the date of hospital discharge or death, whichever comes first. The incidence of new mechanical ventilation uses from the date of randomization until the last day of the study and the duration of it will be extracted. Please note that we are trying to add further secondary outcomes and this section of the protocol is still evolving. RANDOMIZATION: Eligible patients with confirmed SARS-Cov-2 infections will be randomly assigned in a 1:1 ratio to two therapeutic arms using permuted, block-randomization to balance the number of patients allocated to each group. The permuted block (three or six patients per block) randomization sequence will be generated, using Package 'randomizeR' in R software version 3.6.1. and placed in individual sealed and opaque envelopes by the statistician. The investigator will enroll the patients and only then open envelopes to assign patients to the different treatment groups. This method of allocation concealment will result in minimum selection and confounding biases. BLINDING (MASKING): The present research is open-label (no masking) of patients and health care professionals who are undertaking outcome assessment of the primary outcome - time to clinical improvement. NUMBERS TO BE RANDOMISED (SAMPLE SIZE): Of the 100 patients randomised, 50 patients will be assigned to receive high dose Interferon beta-1a plus lopinavir/ritonavir (Kaletra), 50 patients will be assigned to receive low dose Interferon beta 1a plus lopinavir/ritonavir (Kaletra). TRIAL STATUS: Protocol version 1.2.1. Recruitment is finished, the start date of recruitment was on August 20th 2020, and the end date was on September 4th 2020. Last point of data collection will be the last day on which all of the 100 participants have had an outcome of clinical improvement or death, up to 14th days after hospitalization. TRIAL REGISTRATION: This study was registered with National Institutes of Health Clinical trials ( www.clinicaltrials.gov ; identification number NCT04521400, https://clinicaltrials.gov/ct2/show/NCT04521400 , registered August 18, 2020 and first available online August 20, 2020). FULL PROTOCOL: The full protocol is attached as an additional file, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol.

Incidence and clinical profiles of COVID-19 pneumonia in pregnant women: A single-centre cohort study from Spain.

BACKGROUND: Information regarding the incidence and characteristics of COVID-19 pneumonia amongst pregnant women is scarce. METHODS: Single-centre experience with 32 pregnant women diagnosed with COVID-19 between March 5 to April 5, 2020 at Madrid, Spain. FINDINGS: COVID-19 pneumonia was diagnosed in 61·5% (32/52) women. Only 18·7% (6/32) had some underlying condition (mostly asthma). Supplemental oxygen therapy was required in 18 patients (56·3%), with high-flow requirements in six (18·7%). Eight patients (25·0%) fulfilled the criteria for acute distress respiratory syndrome. Invasive mechanical ventilation was required in two patients (6·2%). Tocilizumab was administered in five patients (15·6%). Delivery was precipitated due to COVID-19 in three women (9·4%). All the newborns had a favourable outcome, with no cases of neonatal SARS-CoV-2 transmission. Severe cases of pneumonia requiring supplemental oxygen were more likely to exhibit bilateral alveolar or interstitial infiltrates on chest X-ray (55·6% vs. 0·0%; P-value = 0·003) and serum C-reactive protein (CRP) levels >10 mg/dL (33·0% vs. 0·0%; P-value = 0·05) at admission than those with no oxygen requirements. INTERPRETATION: Pregnant women with COVID-19 have a high risk of developing pneumonia, with a severe course in more than half of cases. The presence of bilateral kung infiltrates and elevated serum CRP at admission may identify women at-risk of severe COVID-19 pneumonia. FUNDING: Instituto de Salud Carlos III (COV20/00,181), Spanish Ministry of Science and Innovation.

Effectiveness of Interferon Beta 1a, compared to Interferon Beta 1b and the usual therapeutic regimen to treat adults with moderate to severe COVID-19: structured summary of a study protocol for a randomized controlled trial.

OBJECTIVES: We will investigate the effectiveness of Interferon Beta 1a, compared to Interferon Beta 1b and the usual therapeutic regimen in COVID-19 in patients that have tested positive and are moderately to severely ill. TRIAL DESIGN: This is a single center, open label, randomized, controlled, parallel group, clinical trial that will be conducted at Loghman Hakim Medical Education Center in conjunction with Shahid Beheshti University of Medical Sciences. PARTICIPANTS: Sixty COVID-19 confirmed cases (using the RT-PCR test) will be enrolled in the trial between April 9th to April 14th 2020. Patients will be randomly assigned to the intervention groups or the control group with the following eligibility criteria: ≥ 18 years of age AND (oxygen saturation (SPO2) ≤ 93% OR respiratory rate ≥ 24) AND at least one of the following: Contactless infrared forehead thermometer temperature of ≥37.8, cough, sputum production, nasal discharge, myalgia, headache or fatigue on admission, and time of onset of the symptoms should be acute (Days ≤ 14). Although Hydroxychloroquine will be administered in a single dose, patients with heart problems (prolonged QT or PR intervals, second- or third-degree heart block, and arrhythmias including torsade de pointes) will be excluded. Other exclusion criteria include using drugs with potential interaction with Hydroxychloroquine + Lopinavir/Ritonavir, Interferon-ß 1a, Interferon-ß 1b, pregnant or lactating women, history of alcohol or drug addiction in the past 5 years, blood ALT/AST levels > 5 times the upper limit of normal on laboratory results and refusal to participate. This study will be undertaken at the Loghman Hakim Hospital, Shahid Beheshti University of Medical Sciences and Health Services. INTERVENTION AND COMPARATOR: COVID-19 confirmed patients will be randomly assigned to one of three groups, with 20 patients in each. The first group (Arm 1) will receive Hydroxychloroquine + Lopinavir / Ritonavir (Kaletra) + Interferon-ß 1a (Recigen), the second group (Arm 2) will be administered Hydroxychloroquine + Lopinavir / Ritonavir (Kaletra) + Interferon-ß 1b (Ziferon), and the control group (Arm 3) will be treated by Hydroxychloroquine + Lopinavir / Ritonavir (Kaletra). MAIN OUTCOMES: Time to clinical improvement is our primary outcome measure. This is an improvement of two points on a seven-category ordinal scale (recommended by the World Health Organization: Coronavirus disease (COVID-2019) R&D. Geneva: World Health Organization) or discharge from the hospital, whichever comes first. Secondary outcomes include mortality from the date of randomization until the last day of the study which will be the day all of the patients have had at least one of the following outcomes: 1) Improvement of two points on a seven-category ordinal scale. 2) Discharge from the hospital 3) Death. If any patient dies, we have reached an important secondary outcome. SpO2 Improvement between the last and first day of hospitalization, using pulse-oximetry. Duration of hospitalization from date of randomization until the date of hospital discharge or date of death from any cause, whichever comes first. Incidence of new mechanical ventilation uses from date of randomization until the last day of the study. Please note that we are trying to add further secondary outcomes and this section of the protocol is still evolving. Statistical analysis will be performed by R version 3.6.1 software. We will use Kaplan-Meier to analyze the time to clinical improvement (compared with a log-rank test). Hazard ratios with 95% confidence intervals will be calculated using the Cox proportional-hazards model in crude and adjusted analysis. RANDOMIZATION: Eligible patients will be randomly assigned in a 1:1:1 ratio to receive either Interferon Beta 1a, Interferon Beta 1b or standard care only. Patients will be randomly allocated to three therapeutic arms using permuted, block-randomization to balance the number of patients allocated to each group. The permuted block (three or six patients per block) randomization sequence will be generated, using Package 'randomizeR' in R software version 3.6.1. and placed in individual sealed and opaque envelopes by the statistician. The investigator will enroll the patients and only then open envelopes to assign patients to the different treatment groups. This method of allocation concealment will result in minimum selection and confounding biases. BLINDING (MASKING): The present research is open-label (no masking) of patients and health care professionals who are undertaking outcome assessment of the primary outcome - time to clinical improvement. NUMBERS TO BE RANDOMIZED (SAMPLE SIZE): Of the 60 patients who underwent randomization, 20 patients were assigned to receive Interferon beta-1a, 20 patients were assigned to receive Interferon beta 1b plus standard care and the rest of patients were assigned to receive the standard care alone. TRIAL STATUS: Protocol version 1.2.1. Recruitment is finished, the start date of recruitment was on 9th April 2020 and the end date was on 14th April 2020. Last point of data collection will be the last day on which all of the 60 participants have had an outcome of clinical improvement or death, completing the study's follow-up time window. TRIAL REGISTRATION: This study was registered with National Institutes of Health Clinical trials (www.clinicaltrials.gov; identification number NCT04343768, registered April 8, 2020 and first available online April 13, 2020). FULL PROTOCOL: The full protocol is attached as an additional file, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol.

Middle East Respiratory Syndrome Coronavirus Nucleocapsid Protein Suppresses Type I and Type III Interferon Induction by Targeting RIG-I Signaling.

Type I and type III interferons (IFNs) are the frontline of antiviral defense mechanisms that trigger hundreds of downstream antiviral genes. In this study, we observed that MERS-CoV nucleocapsid (N) protein suppresses type I and type III IFN gene expression. The N protein suppresses Sendai virus-induced IFN-ß and IFN-λ1 by reducing their promoter activity and mRNA levels, as well as downstream IFN-stimulated genes (ISGs). Retinoic acid-inducible gene I (RIG-I) is known to recognize viral RNA and induce IFN expression through tripartite motif-containing protein 25 (TRIM25)-mediated ubiquitination of RIG-I caspase activation and recruitment domains (CARDs). We discovered that MERS-CoV N protein suppresses RIG-I-CARD-induced, but not MDA5-CARD-induced, IFN-ß and IFN-λ1 promoter activity. By interacting with TRIM25, N protein impedes RIG-I ubiquitination and activation and inhibits the phosphorylation of transcription factors IFN-regulatory factor 3 (IRF3) and NF-κB that are known to be important for IFN gene activation. By employing a recombinant Sindbis virus-EGFP replication system, we showed that viral N protein downregulated the production of not only IFN mRNA but also bioactive IFN proteins. Taken together, MERS-CoV N protein functions as an IFN antagonist. It suppresses RIG-I-induced type I and type III IFN production by interfering with TRIM25-mediated RIG-I ubiquitination. Our study sheds light on the pathogenic mechanism of how MERS-CoV causes disease.IMPORTANCE MERS-CoV causes death of about 35% of patients. Published studies showed that some coronaviruses are capable of suppressing interferon (IFN) expression in the early phase of infection and MERS-CoV proteins can modulate host immune response. In this study, we demonstrated that MERS-CoV nucleocapsid (N) protein suppresses the production of both type I and type III IFNs via sequestering TRIM25, an E3 ubiquitin ligase that is essential for activating the RIG-I signaling pathway. Ectopic expression of TRIM25 rescues the suppressive effect of the N protein. In addition, the C-terminal domain of the viral N protein plays a pivotal role in the suppression of IFN-ß promoter activity. Our findings reveal how MERS-CoV evades innate immunity and provide insights into the interplay between host immune response and viral pathogenicity.