mRNA 3'UTR lengthening by alternative polyadenylation attenuates inflammatory responses and correlates with virulence of Influenza A virus.

Changes of mRNA 3'UTRs by alternative polyadenylation (APA) have been associated to numerous pathologies, but the mechanisms and consequences often remain enigmatic. By combining transcriptomics, proteomics and recombinant viruses we show that all tested strains of IAV, including A/PR/8/34(H1N1) (PR8) and A/Cal/07/2009 (H1N1) (Cal09), cause APA. We mapped the effect to the highly conserved glycine residue at position 184 (G184) of the viral non-structural protein 1 (NS1). Unbiased mass spectrometry-based analyses indicate that NS1 causes APA by perturbing the function of CPSF4 and that this function is unrelated to virus-induced transcriptional shutoff. Accordingly, IAV strain PR8, expressing an NS1 variant with weak CPSF binding, does not induce host shutoff but only APA. However, recombinant IAV (PR8) expressing NS1(G184R) lacks binding to CPSF4 and thereby also the ability to cause APA. Functionally, the impaired ability to induce APA leads to an increased inflammatory cytokine production and an attenuated phenotype in a mouse infection model. Investigating diverse viral infection models showed that APA induction is a frequent ability of many pathogens. Collectively, we propose that targeting of the CPSF complex, leading to widespread alternative polyadenylation of host transcripts, constitutes a general immunevasion mechanism employed by a variety of pathogenic viruses.

IFN-λ is protective against lethal oral Toxoplasma gondii infection.

Interferons are essential for innate and adaptive immune responses against a wide variety of pathogens. Interferon lambda (IFN-λ) protects mucosal barriers during pathogen exposure. The intestinal epithelium is the first contact site for Toxoplasma gondii (T. gondii) with its hosts and the first defense line that limits parasite infection. Knowledge of very early T. gondii infection events in the gut tissue is limited and a possible contribution of IFN-λ has not been investigated so far. Here, we demonstrate with systemic interferon lambda receptor (IFNLR1) and conditional (Villin-Cre) knockout mouse models and bone marrow chimeras of oral T. gondii infection and mouse intestinal organoids a significant impact of IFN-λ signaling in intestinal epithelial cells and neutrophils to T. gondii control in the gastrointestinal tract. Our results expand the repertoire of interferons that contribute to the control of T. gondii and may lead to novel therapeutic approaches against this world-wide zoonotic pathogen.

Interferon Lambda Regulates Cellular and Humoral Immunity in Pristane-Induced Lupus.

A pivotal role of type I interferons in systemic lupus erythematosus (SLE) is widely accepted. Type III interferons (IFN-λ) however, the most recently discovered cytokines grouped within the interferon family, have not been extensively studied in lupus disease models yet. Growing evidence suggests a role for IFN-λ in regulating both innate and adaptive immune responses, and increased serum concentrations have been described in multiple autoimmune diseases including SLE. Using the pristane-induced lupus model, we found that mice with defective IFN-λ receptors (Ifnlr1-/-) showed increased survival rates, decreased lipogranuloma formation and reduced anti-dsDNA autoantibody titers in the early phase of autoimmunity development compared to pristane-treated wild-type mice. Moreover, Ifnlr1-/- mice treated with pristane had reduced numbers of inflammatory mononuclear phagocytes and cNK cells in their kidneys, resembling untreated control mice. Systemically, circulating B cells and monocytes (CD115+Ly6C+) were reduced in pristane-treated Ifnlr1-/- mice. The present study supports a significant role for type III interferons in the pathogenesis of pristane-induced murine autoimmunity as well as in systemic and renal inflammation. Although the absence of type III interferon receptors does not completely prevent the development of autoantibodies, type III interferon signaling accelerates the development of autoimmunity and promotes a pro-inflammatory environment in autoimmune-prone hosts.

Interferon-λ Improves the Efficacy of Intranasally or Rectally Administered Influenza Subunit Vaccines by a Thymic Stromal Lymphopoietin-Dependent Mechanism.

Previous work showed that interferon-λ (IFN-λ) can trigger the synthesis of thymic stromal lymphopoietin (TSLP) by specialized epithelial cells in the upper airways of mice, thereby improving the performance of intranasally administered influenza vaccines. Here we demonstrate that protein-only influenza vaccines containing either IFN-λ or TSLP boosted antigen-specific IgG1 and IgA responses and enhanced the resistance of mice to influenza virus challenge, irrespective of whether the vaccines were applied via the intranasal or the rectal route. TSLP receptor deficiency negatively influenced vaccine-induced antiviral immunity by impairing the migration of dendritic cells from the airways to the draining lymph nodes of immunized mice, thereby restraining follicular helper T cell and germinal center B cell responses. As previously observed during intranasal vaccination, the adjuvant effect of IFN-λ on a rectally administered influenza vaccine was no longer observed when TSLP receptor-deficient mice were used for immunization, highlighting the central role of the IFN-λ/TSLP axis for vaccine-induced antiviral immunity in the mucosa.

An affinity-enhanced, broadly neutralizing heavy chain-only antibody protects against SARS-CoV-2 infection in animal models.

Broadly neutralizing antibodies are an important treatment for individuals with coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Antibody-based therapeutics are also essential for pandemic preparedness against future Sarbecovirus outbreaks. Camelid-derived single domain antibodies (VHHs) exhibit potent antimicrobial activity and are being developed as SARS-CoV-2­neutralizing antibody-like therapeutics. Here, we identified VHHs that neutralize both SARS-CoV-1 and SARS-CoV-2, including now circulating variants. We observed that the VHHs bound to a highly conserved epitope in the receptor binding domain of the viral spike protein that is difficult to access for human antibodies. Structure-guided molecular modeling, combined with rapid yeast-based prototyping, resulted in an affinity enhanced VHH-human immunoglobulin G1 Fc fusion molecule with subnanomolar neutralizing activity. This VHH-Fc fusion protein, produced in and purified from cultured Chinese hamster ovary cells, controlled SARS-CoV-2 replication in prophylactic and therapeutic settings in mice expressing human angiotensin converting enzyme 2 and in hamsters infected with SARS-CoV-2. These data led to affinity-enhanced selection of the VHH, XVR011, a stable anti­COVID-19 biologic that is now being evaluated in the clinic.

Rare variant MX1 alleles increase human susceptibility to zoonotic H7N9 influenza virus.

Zoonotic avian influenza A virus (IAV) infections are rare. Sustained transmission of these IAVs between humans has not been observed, suggesting a role for host genes. We used whole-genome sequencing to compare avian IAV H7N9 patients with healthy controls and observed a strong association between H7N9 infection and rare, heterozygous single-nucleotide variants in the MX1 gene. MX1 codes for myxovirus resistance protein A (MxA), an interferon-induced antiviral guanosine triphosphatase known to control IAV infections in transgenic mice. Most of the MxA variants identified lost the ability to inhibit avian IAVs, including H7N9, in transfected human cell lines. Nearly all of the inactive MxA variants exerted a dominant-negative effect on the antiviral function of wild-type MxA, suggesting an MxA null phenotype in heterozygous carriers. Our study provides genetic evidence for a crucial role of the MX1-based antiviral defense in controlling zoonotic IAV infections in humans.

Rotavirus susceptibility of antibiotic-treated mice ascribed to diminished expression of interleukin-22.

The commensal microbiota regulates susceptibility to enteric pathogens by fine-tuning mucosal innate immune responses, but how susceptibility to enteric viruses is shaped by the microbiota remains incompletely understood. Past reports have indicated that commensal bacteria may either promote or repress rotavirus replication in the small intestine of mice. We now report that rotavirus replicated more efficiently in the intestines of germ-free and antibiotic-treated mice compared to animals with an unmodified microbiota. Antibiotic treatment also facilitated rotavirus replication in type I and type III interferon (IFN) receptor-deficient mice, revealing IFN-independent proviral effects. Expression of interleukin-22 (IL-22) was strongly diminished in the intestine of antibiotic-treated mice. Treatment with exogenous IL-22 blocked rotavirus replication in microbiota-depleted wild-type and Stat1-/- mice, demonstrating that the antiviral effect of IL-22 in animals with altered microbiome is not dependent on IFN signaling. In antibiotic-treated animals, IL-22-induced a specific set of genes including Fut2, encoding fucosyl-transferase 2 that participates in the biosynthesis of fucosylated glycans which can mediate rotavirus binding. Interestingly, IL-22 also blocked rotavirus replication in antibiotic-treated Fut2-/- mice. Furthermore, IL-22 inhibited rotavirus replication in antibiotic-treated mice lacking key molecules of the necroptosis or pyroptosis pathways of programmed cell death. Taken together, our results demonstrate that IL-22 determines rotavirus susceptibility of antibiotic-treated mice, yet the IL-22-induced effector molecules conferring rotavirus resistance remain elusive.

Selective Janus kinase inhibition preserves interferon-λ-mediated antiviral responses.

Inflammatory diseases are frequently treated with Janus kinase (JAK) inhibitors to diminish cytokine signaling. These treatments can lead to inadvertent immune suppression and may increase the risk of viral infection. Tyrosine kinase 2 (TYK2) is a JAK family member required for efficient type I interferon (IFN-α/ß) signaling. We report here that selective TYK2 inhibition preferentially blocked potentially detrimental type I IFN signaling, whereas IFN-λ-mediated responses were largely preserved. In contrast, the clinically used JAK1/2 inhibitor baricitinib was equally potent in blocking IFN-α/ß- or IFN-λ-driven responses. Mechanistically, we showed that epithelial cells did not require TYK2 for IFN-λ-mediated signaling or antiviral protection. TYK2 deficiency diminished IFN-α-induced protection against lethal influenza virus infection in mice but did not impair IFN-λ-mediated antiviral protection. Our findings suggest that selective TYK2 inhibitors used in place of broadly acting JAK1/2 inhibitors may represent a superior treatment option for type I interferonopathies to counteract inflammatory responses while preserving antiviral protection mediated by IFN-λ.

Microbiota-dependent increase in δ-valerobetaine alters neuronal function and is responsible for age-related cognitive decline.

Understanding the physiological origins of age-related cognitive decline is of critical importance given the rising age of the world's population1. Previous work in animal models has established a strong link between cognitive performance and the microbiota2-5, and it is known that the microbiome undergoes profound remodeling in older adults6. Despite growing evidence for the association between age-related cognitive decline and changes in the gut microbiome, the mechanisms underlying such interactions between the brain and the gut are poorly understood. Here, using fecal microbiota transplantation (FMT), we demonstrate that age-related remodeling of the gut microbiota leads to decline in cognitive function in mice and that this impairment can be rescued by transplantation of microbiota from young animals. Moreover, using a metabolomic approach, we found elevated concentrations of δ-valerobetaine, a gut microbiota-derived metabolite, in the blood and brain of aged mice and older adults. We then demonstrated that δ-valerobetaine is deleterious to learning and memory processes in mice. At the neuronal level, we showed that δ-valerobetaine modulates inhibitory synaptic transmission and neuronal network activity. Finally, we identified specific bacterial taxa that significantly correlate with δ-valerobetaine levels in the brain. Based on our findings, we propose that δ-valerobetaine contributes to microbiota-driven brain aging and that the associated mechanisms represent a promising target for countering age-related cognitive decline.

Antagonism of interferon signaling by fibroblast growth factors promotes viral replication.

Fibroblast growth factors (FGFs) play key roles in the pathogenesis of different human diseases, but the cross-talk between FGFs and other cytokines remains largely unexplored. We identified an unexpected antagonistic effect of FGFs on the interferon (IFN) signaling pathway. Genetic or pharmacological inhibition of FGF receptor signaling in keratinocytes promoted the expression of interferon-stimulated genes (ISG) and proteins in vitro and in vivo. Conversely, FGF7 or FGF10 treatment of keratinocytes suppressed ISG expression under homeostatic conditions and in response to IFN or poly(I:C) treatment. FGF-mediated ISG suppression was independent of IFN receptors, occurred at the transcriptional level, and required FGF receptor kinase and proteasomal activity. It is not restricted to keratinocytes and functionally relevant, since FGFs promoted the replication of herpes simplex virus I (HSV-1), lymphocytic choriomeningitis virus, and Zika virus. Most importantly, inhibition of FGFR signaling blocked HSV-1 replication in cultured human keratinocytes and in mice. These results suggest the use of FGFR kinase inhibitors for the treatment of viral infections.

Different effects of constitutive and induced microbiota modulation on microglia in a mouse model of Alzheimer's disease.

It was recently revealed that gut microbiota promote amyloid-beta (Aß) burden in mouse models of Alzheimer's disease (AD). However, the underlying mechanisms when using either germ-free (GF) housing conditions or treatments with antibiotics (ABX) remained unknown. In this study, we show that GF and ABX-treated 5x familial AD (5xFAD) mice developed attenuated hippocampal Aß pathology and associated neuronal loss, and thereby delayed disease-related memory deficits. While Aß production remained unaffected in both GF and ABX-treated 5xFAD mice, we noticed in GF 5xFAD mice enhanced microglial Aß uptake at early stages of the disease compared to ABX-treated 5xFAD mice. Furthermore, RNA-sequencing of hippocampal microglia from SPF, GF and ABX-treated 5xFAD mice revealed distinct microbiota-dependent gene expression profiles associated with phagocytosis and altered microglial activation states. Taken together, we observed that constitutive or induced microbiota modulation in 5xFAD mice differentially controls microglial Aß clearance mechanisms preventing neurodegeneration and cognitive deficits.

Interferon-λ Receptor Expression: Novel Reporter Mouse Reveals Within- and Cross-Tissue Heterogeneity.

Interferon-λ (IFN-λ) plays an important role in mucosal immunity, but reliable information regarding the expression of the IFN-λ receptor in individual cells is still missing. One reason for this knowledge gap is the lack of antibodies that specifically recognize the unique IFNLR1 subunit of the dimeric IFN-λ receptor complex. In this study, we investigated whether a reporter mouse carrying a bacterial ß-galactosidase gene inserted into the Ifnlr1 locus could be used to visualize IFN-λ receptor-expressing cells in whole organs. First we confirmed that insertion of the reporter cassette inactivated the Ifnlr1 gene, and that gene function could be restored by removing the ß-galactosidase insert by site-specific recombination. When whole tissues were analyzed, prominent ß-galactosidase activity was confined to the intestinal tract of reporter mice. However, only the snout expressed ß-galactosidase at levels high enough for reliable detection in whole tissue extracts. Interestingly, individual epithelial cells in the upper airways expressed ß-galactosidase activity to variable degrees as determined by flow cytometry and histology, suggesting a remarkable heterogeneity in IFNLR1 expression levels. Taken together, our results demonstrate a surprisingly strong within- and cross-tissue heterogeneity of IFNLR1 expression that may have physiological implications.

Prevention of influenza virus infection and transmission by intranasal administration of a porous maltodextrin nanoparticle-formulated vaccine.

Influenza vaccines administered intramuscularly exhibit poor mucosal immune responses in the respiratory tract which is the prime site of the infection. Intranasal vaccination is a potential route for vaccine delivery which has been demonstrated effective in inducing protective immune responses in both systemic and mucosal compartments. For this purpose, nanoparticles have been used as antigen delivery systems to improve antigen capture by immune cells. In this paper we demonstrate efficient delivery of viral antigens to airway epithelial cells, macrophages and dendritic cells, using polysaccharide nanoparticles (NPL), leading to a strong protection against influenza virus infection. A formulation combining split Udorn virus antigens with NPL and the mucosal protein adjuvant CTA1-DD was administered intranasally and resulted in an enhanced specific humoral immune response. Furthermore, NPL carrying split Udorn, with or without CTA1-DD, inhibited virus transmission from infected to uninfected naive mice. These results demonstrate that an intranasal delivery system combining NPL, mucosal adjuvant CTA1-DD and split virus antigens confers robust protection against influenza infection and inhibits virus transmission.

A dual role for hepatocyte-intrinsic canonical NF-κB signaling in virus control.

BACKGROUND & AIMS: Hepatic innate immune control of viral infections has largely been attributed to Kupffer cells, the liver-resident macrophages. However, hepatocytes, the parenchymal cells of the liver, also possess potent immunological functions in addition to their known metabolic functions. Owing to their abundance in the liver and known immunological functions, we aimed to investigate the direct antiviral mechanisms employed by hepatocytes. METHODS: Using lymphocytic choriomeningitis virus (LCMV) as a model of liver infection, we first assessed the role of myeloid cells by depletion prior to infection. We investigated the role of hepatocyte-intrinsic innate immune signaling by infecting mice lacking canonical NF-κB signaling (IkkßΔHep) specifically in hepatocytes. In addition, mice lacking hepatocyte-specific interferon-α/ß signaling-(IfnarΔHep), or interferon-α/ß signaling in myeloid cells-(IfnarΔMyel) were infected. RESULTS: Here, we demonstrate that LCMV activates NF-κB signaling in hepatocytes. LCMV-triggered NF-κB activation in hepatocytes did not depend on Kupffer cells or TNFR1 signaling but rather on Toll-like receptor signaling. LCMV-infected IkkßΔHep livers displayed strongly elevated viral titers due to LCMV accumulation within hepatocytes, reduced interferon-stimulated gene (ISG) expression, delayed intrahepatic immune cell influx and delayed intrahepatic LCMV-specific CD8+ T cell responses. Notably, viral clearance and ISG expression were also reduced in LCMV-infected primary hepatocytes lacking IKKß, demonstrating a hepatocyte-intrinsic effect. Similar to livers of IkkßΔHep mice, enhanced hepatocytic LCMV accumulation was observed in livers of IfnarΔHep mice, whereas IfnarΔMyel mice were able to control LCMV infection. Hepatocytic NF-κB signaling was also required for efficient ISG induction in HDV-infected dHepaRG cells and interferon-α/ß-mediated inhibition of HBV replication in vitro. CONCLUSIONS: Together, these data show that hepatocyte-intrinsic NF-κB is a vital amplifier of interferon-α/ß signaling, which is pivotal for strong early ISG responses, immune cell infiltration and hepatic viral clearance. LAY SUMMARY: Innate immune cells have been ascribed a primary role in controlling viral clearance upon hepatic infections. We identified a novel dual role for NF-κB signaling in infected hepatocytes which was crucial for maximizing interferon responses and initiating adaptive immunity, thereby efficiently controlling hepatic virus replication.

The alternative cap-binding complex is required for antiviral defense in vivo.

Cellular response to environmental challenges requires immediate and precise regulation of transcriptional programs. During viral infections, this includes the expression of antiviral genes that are essential to combat the pathogen. Transcribed mRNAs are bound and escorted to the cytoplasm by the cap-binding complex (CBC). We recently identified a protein complex consisting of NCBP1 and NCBP3 that, under physiological conditions, has redundant function to the canonical CBC, consisting of NCBP1 and NCBP2. Here, we provide evidence that NCBP3 is essential to mount a precise and appropriate antiviral response. Ncbp3-deficient cells allow higher virus growth and elicit a reduced antiviral response, a defect happening on post-transcriptional level. Ncbp3-deficient mice suffered from severe lung pathology and increased morbidity after influenza A virus challenge. While NCBP3 appeared to be particularly important during viral infections, it may be more broadly involved to ensure proper protein expression.

Influenza restriction factor MxA functions as inflammasome sensor in the respiratory epithelium.

The respiratory epithelium is exposed to the environment and initiates inflammatory responses to exclude pathogens. Influenza A virus (IAV) infection triggers inflammatory responses in the respiratory mucosa, but the mechanisms of inflammasome activation are poorly understood. We identified MxA as a functional inflammasome sensor in respiratory epithelial cells that recognizes IAV nucleoprotein and triggers the formation of ASC (apoptosis-associated speck-like protein containing a CARD) specks via interaction of its GTPase domain with the PYD domain of ASC. ASC specks were present in bronchiolar epithelial cells of IAV-infected MxA-transgenic mice, which correlated with early IL-1ß production and early recruitment of granulocytes in the lungs of infected mice. Collectively, these results demonstrate that MxA contributes to IAV resistance by triggering a rapid inflammatory response in infected respiratory epithelial cells.

Type I and Type III Interferons Differ in Their Adjuvant Activities for Influenza Vaccines.

Type I and type III interferons (IFNs) can promote adaptive immune responses in mice and improve vaccine-induced resistance to viral infections. The adjuvant effect of type III IFN (IFN-λ) specifically boosts mucosal immunity by an indirect mechanism, involving IFN-λ-induced production of thymic stromal lymphopoietin (TSLP), a cytokine that activates immune cells. To date, it remained unclear whether the previously described adjuvant effect of type I IFN (IFN-α/ß) would also depend on TSLP and whether type I IFN stimulates different antibody subtypes. Here, we show that after infection with a live attenuated influenza virus, mice lacking functional type I IFN receptors failed to produce normal amounts of virus-specific IgG2c and IgA antibodies. In contrast, mice lacking functional IFN-λ receptors contained normal levels of virus-specific IgG2c but had reduced IgG1 and IgA antibody levels. When applied together with protein antigen, IFN-α stimulated the production of antigen-specific IgA and IgG2c to a greater extent than IgG1, irrespective of whether the mice expressed functional TSLP receptors and irrespective of whether the vaccine was applied by the intranasal or the intraperitoneal route. Taken together, these results demonstrate that the adjuvant activities of type I and type III IFNs are mechanistically distinct.IMPORTANCE Interferons can shape antiviral immune responses, but it is not well understood how they influence vaccine efficacy. We find that type I IFN preferentially promotes the production of antigen-specific IgG2c and IgA antibodies after infection with a live attenuated influenza virus or after immunization with influenza subunit vaccines. In contrast, type III IFN specifically enhances influenza virus-specific IgG1 and IgA production. The adjuvant effect of type I IFN was not dependent on TSLP, which is essential for the adjuvant effect of type III IFN. Type I IFN boosted vaccine-induced antibody production after immunization by the intranasal or the intraperitoneal route, whereas type III IFN exhibited its adjuvant activity only when the vaccine was delivered by the mucosal route. Our findings demonstrate that type I and type III IFNs trigger distinct pathways to enhance the efficacy of vaccines. This knowledge might be used to design more efficient vaccines against infectious diseases.

Microbiota-Driven Tonic Interferon Signals in Lung Stromal Cells Protect from Influenza Virus Infection.

Type I interferon (IFNα/ß) pathways are fine-tuned to elicit antiviral protection while minimizing immunopathology; however, the initiating stimuli, target tissues, and underlying mechanisms are unclear. Using models of physiological and dysregulated IFNα/ß receptor (IFNAR1) surface expression, we show here that IFNAR1-dependent signals set the steady-state IFN signature in both hematopoietic and stromal cells. Increased IFNAR1 levels promote a lung environment refractory to early influenza virus replication by elevating the baseline interferon signature. Commensal microbiota drive the IFN signature specifically in lung stroma, as shown by antibiotic treatment and fecal transplantation. Bone marrow chimera experiments identify lung stromal cells as crucially important for early antiviral immunity and stroma-immune cell interaction for late antiviral resistance. We propose that the microbiota-driven interferon signature in lung epithelia impedes early virus replication and that IFNAR1 surface levels fine-tune this signature. Our findings highlight the interplay between bacterial and viral exposure, with important implications for antibiotic use.

Interferon-λ orchestrates innate and adaptive mucosal immune responses.

Type III interferon (IFN-λ) was initially thought to have functions similar to those of the type I interferons (IFN-α and IFN-ß). New findings have indicated, however, that IFN-λ has a non-redundant role in the innate antiviral, antifungal and antiprotozoal defences of mucosal barriers. In this Review, we highlight recent work showing that IFN-λ inhibits virus dissemination within the body and limits the transmission of respiratory and gastrointestinal viruses to naive hosts. We also discuss findings indicating that IFN-λ can act on neutrophils to prevent invasive pulmonary aspergillosis. We summarize results showing that IFN-λ signalling differs in several respects from IFN-α and IFN-ß signalling, particularly in neutrophils. Finally, we discuss new findings indicating that IFN-λ is a potent enhancer of adaptive immune responses in the respiratory mucosa.