Defining the distinct, intrinsic properties of the novel type I interferon, IFNϵ

Expression of Interferon Epsilon in Mucosal Epithelium is Regulated by Elf3

Interferon epsilon (IFNε) is a unique type I interferon (IFN) that shows distinct constitutive expression in reproductive tract epithelium. Understanding how IFNε expression is regulated is critical for the mechanism of action in protecting the mucosa from infection. Combined computational and experimental investigation of the promoter of IFNε predicted transcription factor binding sites for the ETS family of transcription factors. We demonstrate here that Ifnε is regulated by Elf3, an epithelial restricted member of the ETS family. It is co-expressed with IFNε at the epithelium of uterus, lung and intestine, and we focused on regulation of IFNε expression in the uterus. Promoter reporter studies demonstrated that Elf3 was a strong driver of Ifnε expression; knockdown of Elf3 reduced expression levels of IFNε; Elf3 regulated Ifnε expression and chromatin immunoprecipitation (ChIP) confirmed the direct binding of Elf3 to the IFNε promoter. These data show that Elf3 is important in regulating protective mucosal immunity by driving constitutive expression of IFNε to protect mucosal tissues from infection in at least three organ systems.

Structural and Functional Characterization of a Fish Type I Subgroup d IFN Reveals Its Binding to Receptors

Teleost fish type I IFNs and the associated receptors from the cytokine receptor family B (CRFB) are characterized by remarkable diversity and complexity. How the fish type I IFNs bind to their receptors is still not fully understood. In this study, we demonstrate that CRFB1 and CRFB5 constitute the receptor pair through which type I subgroup d IFN (IFNd) from large yellow croaker, Larimichthys crocea, activates the conserved JAK-STAT signaling pathway as a part of the antiviral response. Our data suggest that L. crocea IFNd (LcIFNd) has a higher binding affinity with L. crocea CRFB5 (LcCRFB5) than with LcCRFB1. Furthermore, we report the crystal structure of LcIFNd at a 1.49-Å resolution and construct structural models of LcIFNd in binary complexes with predicted structures of extracellular regions of LcCRFB1 and LcCRFB5, respectively. Despite striking similarities in overall architectures of LcIFNd and its ortholog human IFN-ω, the receptor binding patterns between LcIFNd and its receptors show that teleost and mammalian type I IFNs may have differentially selected helices that bind to their homologous receptors. Correspondingly, key residues mediating binding of LcIFNd to LcCRFB1 and LcCRFB5 are largely distinct from the receptor-interacting residues in other fish and mammalian type I IFNs. Our findings reveal a ligand/receptor complex binding mechanism of IFNd in teleost fish, thus providing new insights into the function and evolution of type I IFNs.

Structure-function of type I and III interferons

Type I and type III interferons (IFNs) are major components in activating the innate immune response. Common to both are two distinct receptor chains (IFNAR1/IFNAR2 and IFNLR1/IL10R2), which form ternary complexes upon binding their respective ligands. This results in close proximity of the intracellularly associated kinases JAK1 and TYK2, which cross phosphorylate each other, the associated receptor chains, and signal transducer and activator of transcriptions, with the latter activating IFN-stimulated genes. While there are clear similarities in the biological responses toward type I and type III IFNs, differences have been found in their tropism, tuning of activity, and induction of the immune response. Here, we focus on how these differences are embedded in the structure/function relations of these two systems in light of the recent progress that provides in-depth information on the structural assembly of these receptors and their functional implications and how these differ between the mouse and human systems.

Interferon-epsilon is a novel regulator of NK cell responses in the uterus

The uterus is a unique mucosal site where immune responses are balanced to be permissive of a fetus, yet protective against infections. Regulation of natural killer (NK) cell responses in the uterus during infection is critical, yet no studies have identified uterine-specific factors that control NK cell responses in this immune-privileged site. We show that the constitutive expression of IFNε in the uterus plays a crucial role in promoting the accumulation, activation, and IFNγ production of NK cells in uterine tissue during Chlamydia infection. Uterine epithelial IFNε primes NK cell responses indirectly by increasing IL-15 production by local immune cells and directly by promoting the accumulation of a pre-pro-like NK cell progenitor population and activation of NK cells in the uterus. These findings demonstrate the unique features of this uterine-specific type I IFN and the mechanisms that underpin its major role in orchestrating innate immune cell protection against uterine infection.

Upregulation of IFNE in cervical biopsies of patients with high-risk human papillomavirus infections

PROBLEM

Interferon epsilon (IFN-ε) is constitutively expressed in the epithelium of female reproductive tract and confers vital protection against sexually transmitted pathogens in mouse models. However, there is limited insight into the role of IFN-ε in human sexually transmitted infections such as human papillomavirus (HPV).

METHOD OF STUDY

Cervical biopsies were obtained from high-risk (HR) HPV positive (n = 28) and HR-HPV negative (n = 10) women. mRNA expression of IFN-ε in cervical tissues was measured by qPCR. Expression of the IFN-ε protein was determined by Western blot analysis, immunohistochemistry and immunofluorescence staining.

RESULTS

mRNA expression of IFN-ε was higher in the ectocervix than that of other IFNs, and was further upregulated in HR-HPV positive women compared with HR-HPV negative women. Expression of the IFN-ε protein was comparable between HR-HPV infected patients and healthy controls.

CONCLUSIONS

These results reveal differential expression of IFN-ε mRNA between individuals with or without HR-HPV infection, and imply direct or indirect regulatory mechanisms for IFN-ε transcription by HPV. Expression of IFN-ε protein in HPV infections would require further validation.

Epithelially Restricted Interferon Epsilon Protects Against Colitis

BACKGROUND & AIMS

Type I interferon (T1IFN) signalling is crucial for maintaining intestinal homeostasis. We previously found that the novel T1IFN, IFNε, is highly expressed by epithelial cells of the female reproductive tract, where it protects against pathogens. Its function has not been studied in the intestine. We hypothesize that IFNε is important in maintaining intestinal homeostasis.

METHODS

We characterized IFNε expression in mouse and human intestine by immunostaining and studied its function in the dextran sulfate sodium (DSS) colitis model using both genetic knockouts and neutralizing antibody.

RESULTS

We demonstrate that IFNε is expressed in human and mouse intestinal epithelium, and expression is lost in inflammation. Furthermore, we show that IFNε limits intestinal inflammation in mouse models. Regulatory T cell (Treg) frequencies were paradoxically decreased in DSS-treated IFNε-/- mice, suggesting a role for IFNε in maintaining the intestinal Treg compartment. Colitis was ameliorated by transfer of wild-type Tregs into IFNε-/- mice. This demonstrates that IFNε supports intestinal Treg function.

CONCLUSIONS

Overall, we have shown IFNε expression in intestinal epithelium and its critical role in gut homeostasis. Given its known role in the female reproductive tract, we now show IFNε has a protective role across multiple mucosal surfaces.

Functional interferon-epsilon gene polymorphisms and sexually transmitted infections of the endometrium

PROBLEM

Interferon-epsilon (IFNε) is the only type I IFN constitutively expressed in the female reproductive tract and fluctuates across the menstrual cycle in humans. Mouse models show that IFNε protects against Chlamydia trachomatis, Herpes Simplex Virus, HIV, and Zika in mice, but human studies are limited. Bacterial sexually transmitted infections (STI) can ascend to the upper genital tract and cause pelvic inflammatory disease (PID) and subsequent infertility. However, the host immunological mechanisms that play a role in the ascension and infection of the endometrium in individuals with clinically suspected PID are not elucidated.

METHOD OF STUDY

This pilot investigation determined if IFNε gene variants are associated with bacterial vaginosis (BV) and endometrial infection with C. trachomatis, Neisseria gonorrhoeae, and Mycoplasma genitalium using biospecimens from 154 self-report Black individuals who participated in the PID Evaluation and Clinical Health (PEACH) study.

RESULTS

The T allele for rs2039381 was associated with endometrial STI infection (OR 2.7, 95% CI: 1.0-7.1) and the C allele for rs1125488 was inversely associated with BV (OR: .2, 95% CI: .05-.8).

CONCLUSIONS

Few studies have examined IFNε gene variants, our study raises the possibility that IFNε gene variants may be a potential host contributor to STI pathogenesis.

Interferon-ε is a tumour suppressor and restricts ovarian cancer

High-grade serous ovarian cancers have low survival rates because of their late presentation with extensive peritoneal metastases and frequent chemoresistance1, and require new treatments guided by novel insights into pathogenesis. Here we describe the intrinsic tumour-suppressive activities of interferon-ε (IFNε). IFNε is constitutively expressed in epithelial cells of the fallopian tube, the cell of origin of high-grade serous ovarian cancers, and is then lost during development of these tumours. We characterize its anti-tumour activity in several preclinical models: ovarian cancer patient-derived xenografts, orthotopic and disseminated syngeneic models, and tumour cell lines with or without mutations in Trp53 and Brca genes. We use manipulation of the IFNε receptor IFNAR1 in different cell compartments, differential exposure status to IFNε and global measures of IFN signalling to show that the mechanism of the anti-tumour activity of IFNε involves direct action on tumour cells and, crucially, activation of anti-tumour immunity. IFNε activated anti-tumour T and natural killer cells and prevented the accumulation and activation of myeloid-derived suppressor cells and regulatory T cells. Thus, we demonstrate that IFNε is an intrinsic tumour suppressor in the female reproductive tract whose activities in models of established and advanced ovarian cancer, distinct from other type I IFNs, are compelling indications of potential new therapeutic approaches for ovarian cancer.

Interfering with Interferons: A Critical Mechanism for Critical COVID-19 Pneumonia

Infection with SARS-CoV-2 results in clinical outcomes ranging from silent or benign infection in most individuals to critical pneumonia and death in a few. Genetic studies in patients have established that critical cases can result from inborn errors of TLR3- or TLR7-dependent type I interferon immunity, or from preexisting autoantibodies neutralizing primarily IFN-α and/or IFN-ω. These findings are consistent with virological studies showing that multiple SARS-CoV-2 proteins interfere with pathways of induction of, or response to, type I interferons. They are also congruent with cellular studies and mouse models that found that type I interferons can limit SARS-CoV-2 replication in vitro and in vivo, while their absence or diminution unleashes viral growth. Collectively, these findings point to insufficient type I interferon during the first days of infection as a general mechanism underlying critical COVID-19 pneumonia, with implications for treatment and directions for future research.

Isolation and characterization of the mink interferon-epsilon gene and its antiviral activity

The interferon (IFN) response is the first line of defense against viral invasion and thus plays a central role in the regulation of the immune response. IFN-epsilon (IFN-ε) is a newly discovered type I IFN that does not require viral induction, unlike other type I IFNs. IFN-ε is constitutively expressed in epithelial cells and plays an important role in mucosal immunity. In this study, we evaluated the biological activity of the mink-IFN (MiIFN)-ε gene in prokaryotic cells. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to evaluate IFN-ε expression in different mink tissues. MiIFN-ε was highly expressed in brain, lung, tracheal, kidney, intestinal, bladder, ovarian, and testis tissues. There was no significant difference in MiIFN-ε expression between female and male minks, except in the reproductive system. Expression of the small ubiquitin-like modifier (SUMO3)-MiIFN-ε fusion gene was induced by isopropylβ-d-thiogalactoside, and MiIFN-ε was collected after SUMO-specific protease digestion. We tested the antiviral activity of MiIFN-ε against vesicular stomatitis virus (VSV) in epithelial cells of feline kidney 81 (F81). We used qRT-PCR to analyze the expression of several IFN-stimulated genes (ISGs), including ISG15, 2'-5' oligoadenylate synthetase (2'-5'OAS1), and myxovirus resistance protein 1 (Mx1). Recombinant IFN-ε induced high ISG expression in F81 cells. Compared with those in the cell control group, expressions of ISG15, Mx1, and 2'-5' OAS1 in the VSV-GFP control, IFN-ε, and MiIFN-ε-inhibited VSV-GFP groups were significantly increased. Compared with those in the VSV-GFP control group, expressions of ISG15 and 2'-5' OAS1 in the IFN-ε and MiIFN-ε-inhibited VSV-GFP groups were significantly increased, and the differences were highly significant (p < 0.0001). IFN-ε played an indirect antiviral role. These findings lay the foundation for detailed investigation of IFN-ε in the future.

Molecular and Structural Basis of Receptor Binding and Signaling of a Fish Type I IFN with Three Disulfide Bonds

In mammals, type I IFNs, which commonly contain one or two disulfide bonds, activate the JAK-STAT signaling pathway through binding to the common cell surface receptor formed by IFN-α/β receptor (IFNAR)1 and IFNAR2 subunits. Although type I IFNs are also known to be essential for antiviral defense in teleost fish, very little is known about mechanisms underlying the recognition of fish type I IFNs by associated receptors. In this study, we demonstrate that a type I IFN of large yellow croaker Larimichthys crocea (LcIFNi), belonging to a new subgroup of fish type I IFNs, triggers antiviral response via the conserved JAK-STAT pathway through stable binding with a heterodimeric receptor comprising subunits LcCRFB5 and LcCRFB2. LcIFNi binds to LcCRFB5 with a much higher affinity than to LcCRFB2. Furthermore, we determined the crystal structure of LcIFNi at a 1.39 Å resolution. The high-resolution structure is, to our knowledge, the first reported structure of a type I IFN with three disulfide bonds, all of which were found to be indispensable for folding and stability of LcIFNi. Using structural analysis, mutagenesis, and biochemical assays, we identified key LcIFNi residues involved in receptor interaction and proposed a structural model of LcIFNi bound to the LcCRFB2–LcCRFB5 receptor. The results show that LcIFNi–LcCRFB2 exhibits a similar binding pattern to human IFN-ω–IFNAR2, whereas the binding pattern of LcIFNi–LcCRFB5 is quite different from that of IFN-ω–IFNAR1. Altogether, our findings reveal the structural basis for receptor interaction and signaling of a type I IFN with three disulfide bonds and provide new insights into the mechanisms underlying type I IFN recognition in teleosts.

Interferon Epsilon Signaling Confers Attenuated Zika Replication in Human Vaginal Epithelial Cells

Zika virus (ZIKV) is an emerging flavivirus that causes congenital birth defects and neurological compilations in the human host. Although ZIKV is primarily transmitted through infected mosquitos, recent studies reveal sexual contact as a potential transmission route. In vagina-bearing individuals, the vaginal epithelium constitutes the first line of defense against viruses. However, it is unclear how ZIKV interacts with the vaginal epithelium to initiate ZIKV transmission. In this study, we demonstrate that exposing ZIKV to human vaginal epithelial cells (hVECs) resulted in de novo viral RNA replication, increased envelope viral protein production, and a steady, extracellular release of infectious viral particles. Interestingly, our data show that, despite an increase in viral load, the hVECs did not exhibit significant cytopathology in culture as other cell types typically do. Furthermore, our data reveal that the innate antiviral state of hVECs plays a crucial role in preventing viral cytopathology. For the first time, our data show that interferon epsilon inhibits ZIKV replication. Collectively, our results in this study provide a novel perspective on the viral susceptibility and replication dynamics during ZIKV infection in the human vaginal epithelium. These findings will be instrumental towards developing therapeutic agents aimed at eliminating the pathology caused by the virus.

Spatiotemporal regulation of human IFNε and innate immunity in the female reproductive tract

Although published studies have demonstrated that interferon epsilon (IFNε) has a crucial role in regulating protective immunity in the mouse female reproductive tract (mFRT), expression and regulation of IFNε in the human female reproductive tract (hFRT) have not been characterised. To characterise human IFNε, we obtained hFRT samples from a well- characterized cohort of women, enabling us to comprehensively assess ex vivo IFNε expression in the hFRT at various stages of the menstrual cycle. We found that among the various types of IFNs, IFNε is uniquely selectively and constitutively expressed in the hFRT epithelium. It has distinct expression patterns in the surface and glandular epithelia of the upper hFRT compared with basal layers of the stratified squamous epithelia of the lower hFRT. There is cyclical variation of IFNε expression in the endometrial epithelium of the upper hFRT and not in the distal FRT, consistent with selective endometrial expression of the progesterone receptor and regulation of the IFNE promoter by progesterone. Since we show IFNε stimulates important protective IFN-regulated genes (IRGs) in FRT epithelium, this characterisation is a key element in understanding the mechanisms of hormonal control of mucosal immunity.

Defining a role for Interferon Epsilon in normal and complicated pregnancies

Interferon epsilon (IFNe) is a recently described cytokine that is constitutively expressed in the female reproductive tract. However, the role of this hormonally regulated cytokine during human pregnancy is poorly understood. Moreover, whether IFNe participates in host immune response against bacteria-driven intra-amniotic infection or cervical human papillomavirus infection during pregnancy is unknown. Herein, using a unique set of human samples derived from multiple study cohorts, we aimed to uncover the role of IFNe in normal and complicated pregnancies. We showed that IFNe is expressed in the myometrium, cervix, and chorioamniotic membranes, and may therefore represent a constitutive element of host defense mechanisms in these tissues during pregnancy. The expression of IFNe in the myometrium and cervix appeared greater in late gestation than in mid-pregnancy, but did not seem to be impacted by labor. Notably, concentrations of IFNe in amniotic fluid, but not cervical fluid, were increased in a subset of women undergoing spontaneous preterm labor with intra-amniotic infection, indicating that IFNe could participate in anti-microbial responses in the amniotic cavity. However, stimulation with Ureaplasma parvum and/or lipopolysaccharide did not enhance IFNE expression by amnion epithelial or cervical cells in vitro, implicating alternative sources of this cytokine during intra-amniotic or cervical infection, respectively. Collectively, our results represent the first characterization of IFNe expression by human reproductive and gestational tissues during normal pregnancy and suggest a role for this cytokine in intra-amniotic infection leading to preterm birth.

Structural and Functional Analyses of Type I IFNa Shed Light Into Its Interaction With Multiple Receptors in Fish

Teleost type I interferons (IFNs) are categorized into group I and II subgroups that bind to distinct receptors to activate antiviral responses. However, the interaction between ifn ligands and receptors has not fully been understood. In this study, the crystal structure of grass carp [Ctenopharyngodon idella (Ci)] IFNa has been solved at 1.58Å and consists of six helices. The CiIFNa displays a typical structure of type I IFNs with a straight helix F and lacks a helix element in the AB loop. Superposition modeling identified several key residues involved in the interaction with receptors. It was found that CiIFNa bound to cytokine receptor family B (CRFB) 1, CRFB2, and CRFB5, and the three receptors could form heterodimeric receptor complexes. Furthermore, mutation of Leu27, Glu103, Lys117, and His165 markedly decreased the phosphorylation of signal transducer and activator of transcription (STAT) 1a induced by CiIFNa in the Epithelioma papulosum cyprini (EPC) cells, and Glu103 was shown to be required for the CiIFNa-activated antiviral activity. Interestingly, wild-type and mutant CiIFNa proteins did not alter the phosphorylation levels of STAT1b. Our results demonstrate that fish type I IFNs, although structurally conserved, interact with the receptors in a manner that may differ from mammalian homologs.

The Analyses of Cetacean Virus-Responsive Genes Reveal Evolutionary Marks in Mucosal Immunity-Associated Genes

Viruses are the most common and abundant organisms in the marine environment. To better understand how cetaceans have adapted to this virus-rich environment, we compared cetacean virus-responsive genes to those from terrestrial mammals. We identified virus-responsive gene sequences in seven species of cetaceans, which we compared with orthologous sequences in seven terrestrial mammals. As a result of evolution analysis using the branch model and the branch-site model, 21 genes were selected using at least one model. IFN-ε, an antiviral cytokine expressed at mucous membranes, and its receptor IFNAR1 contain cetacean-specific amino acid substitutions that might change the interaction between the two proteins and lead to regulation of the immune system against viruses. Cetacean-specific amino acid substitutions in IL-6, IL-27, and the signal transducer and activator of transcription (STAT)1 are also predicted to alter the mucosal immune response of cetaceans. Since mucosal membranes are the first line of defense against the external environment and are involved in immune tolerance, our analysis of cetacean virus-responsive genes suggests that genes with cetacean-specific mutations in mucosal immunity-related genes play an important role in the protection and/or regulation of immune responses against viruses.

Genetic Modulators of Traumatic Brain Injury in Animal Models and the Impact of Sex-Dependent Effects

Traumatic brain injury (TBI) is a major health problem causing disability and death worldwide. There is no effective treatment, due in part to the complexity of the injury pathology and factors affecting its outcome. The extent of brain injury depends on the type of insult, age, sex, lifestyle, genetic risk factors, socioeconomic status, other co-injuries, and underlying health problems. This review discusses the genes that have been directly tested in TBI models, and whether their effects are known to be sex-dependent. Sex differences can affect the incidence, symptom onset, pathology, and clinical outcomes following injury. Adult males are more susceptible at the acute phase and females show greater injury in the chronic phase. TBI is not restricted to a single sex; despite variations in the degree of symptom onset and severity, it is important to consider both female and male animals in TBI pre-clinical research studies.

The Role of Structure in the Biology of Interferon Signaling

Interferons (IFNs) are a family of cytokines with the unique ability to induce cell intrinsic programs that enhance resistance to viral infection. Induction of an antiviral state at the cell, tissue, organ, and organismal level is performed by three distinct IFN families, designated as Type-I, Type-II, and Type-III IFNs. Overall, there are 21 human IFNs, (16 type-I, 12 IFNαs, IFNβ, IFNϵ, IFNκ, and IFNω; 1 type-II, IFNγ; and 4 type-III, IFNλ1, IFNλ2, IFNλ3, and IFNλ4), that induce pleotropic cellular activities essential for innate and adaptive immune responses against virus and other pathogens. IFN signaling is initiated by binding to distinct heterodimeric receptor complexes. The three-dimensional structures of the type-I (IFNα/IFNAR1/IFNAR2), type-II (IFNγ/IFNGR1/IFNGR2), and type-III (IFNλ3/IFNλR1/IL10R2) signaling complexes have been determined. Here, we highlight similar and unique features of the IFNs, their cell surface complexes and discuss their role in inducing downstream IFN signaling responses.

The Role of Type I Interferons in the Pathogenesis and Treatment of COVID-19

Type I interferons (IFN-I) were first discovered over 60 years ago in a classical experiment by Isaacs and Lindenman, who showed that IFN-Is possess antiviral activity. Later, it became one of the first approved protein drugs using heterologous protein expression systems, which allowed its large-scale production. It has been approved, and widely used in a pleiotropy of diseases, including multiple-sclerosis, hepatitis B and C, and some forms of cancer. Preliminary clinical data has supported its effectiveness against potential pandemic pathogens such as Ebola and SARS. Still, more efficient and specific drugs have taken its place in treating such diseases. The COVID-19 global pandemic has again lifted the status of IFN-Is to become one of the more promising drug candidates, with initial clinical trials showing promising results in reducing the severity and duration of the disease. Although SARS-CoV-2 inhibits the production of IFNβ and thus obstructs the innate immune response to this virus, it is sensitive to the antiviral activity of externally administrated IFN-Is. In this review I discuss the diverse modes of biological actions of IFN-Is and how these are related to biophysical parameters of IFN-I-receptor interaction and cell-type specificity in light of the large variety of binding affinities of the different IFN-I subtypes towards the common interferon receptor. Furthermore, I discuss how these may guide the optimized use IFN-Is in combatting COVID-19.

Common homozygosity for predicted loss-of-function variants reveals both redundant and advantageous effects of dispensable human genes

Humans homozygous or hemizygous for variants predicted to cause a loss of function (LoF) of the corresponding protein do not necessarily present with overt clinical phenotypes. We report here 190 autosomal genes with 207 predicted LoF variants, for which the frequency of homozygous individuals exceeds 1% in at least one human population from five major ancestry groups. No such genes were identified on the X and Y chromosomes. Manual curation revealed that 28 variants (15%) had been misannotated as LoF. Of the 179 remaining variants in 166 genes, only 11 alleles in 11 genes had previously been confirmed experimentally to be LoF. The set of 166 dispensable genes was enriched in olfactory receptor genes (41 genes). The 41 dispensable olfactory receptor genes displayed a relaxation of selective constraints similar to that observed for other olfactory receptor genes. The 125 dispensable nonolfactory receptor genes also displayed a relaxation of selective constraints consistent with greater redundancy. Sixty-two of these 125 genes were found to be dispensable in at least three human populations, suggesting possible evolution toward pseudogenes. Of the 179 LoF variants, 68 could be tested for two neutrality statistics, and 8 displayed robust signals of positive selection. These latter variants included a known FUT2 variant that confers resistance to intestinal viruses, and an APOL3 variant involved in resistance to parasitic infections. Overall, the identification of 166 genes for which a sizeable proportion of humans are homozygous for predicted LoF alleles reveals both redundancies and advantages of such deficiencies for human survival.

PROPERTIES AND FUNCTIONS OF THE NOVEL TYPE I INTERFERON EPSILON

Interferon epsilon (IFNε) is a type I IFN with unusual patterns of expression and therefore, function. It is constitutively expressed by reproductive tract epithelium and regulated by hormones during estrus cycle, reproduction, and menopause and by exogenous hormones. The IFNe protein is encoded by a gene in the type I IFN locus, binds to IFNAR1 and 2 which are required for signaling via the JAK STAT pathway. Its affinity for binding receptors and transducing signals is less potent than IFNα or β subtypes in vitro. Nevertheless, in vivo experiments indicate its efficacy in regulating mucosal immune responses and protecting from bacterial and viral infections. These studies demonstrate a different mechanism of action to type I IFNs. In this organ system with dynamic fluxes in cellularity, requirement to tolerate an implanted fetus, and be protected from disease, there is co-option of a special IFN from a family of effective immunoregulators, with unique controls and modified potency to make it a safe and effective constitutive reproductive tract cytokine.

Shared and Distinct Functions of Type I and Type III Interferons

Type I interferons (IFNs) (IFN-α, IFN-β) and type III IFNs (IFN-λ) share many properties, including induction by viral infection, activation of shared signaling pathways, and transcriptional programs. However, recent discoveries have revealed context-specific functional differences. Here, we provide a comprehensive review of type I and type III IFN activities, highlighting shared and distinct features from molecular mechanisms through physiological responses. Beyond discussing canonical antiviral functions, we consider the adaptive immune priming, anti-tumor, and autoimmune functions of IFNs. We discuss a model wherein type III IFNs serve as a front-line defense that controls infection at epithelial barriers while minimizing damaging inflammatory responses, reserving the more potent type I IFN response for when local responses are insufficient. In this context, we discuss current therapeutic applications targeting these cytokine pathways and highlight gaps in understanding of the biology of type I and type III IFNs in health and disease.

S27 of IFNα1 Contributes to Its Low Affinity for IFNAR2 and Weak Antiviral Activity

Type I interferons (IFNs) signal by forming a high affinity IFN-IFNAR2 dimer, which subsequently recruits IFNAR1 to form a ternary complex that initiates JAK/STAT signaling. Among the 12 IFNα subtypes, IFNα1 has a uniquely low affinity for IFNAR2 (<100 × of the other IFNα subtypes) and commensurately weak antiviral activity, suggesting an undefined function distinct from suppression of viral infections. Also unique in IFNα1 is substitution of a serine for phenylalanine at position 27, a contact point that stabilizes the IFNα:IFNAR2 hydrophobic interface. To determine whether IFNα1-S27 contributes to the low affinity for IFNAR2, we created an IFNα1 mutein, IFNα1-S27F, and compared it to wild-type IFNα1 and IFNα2. Substitution of phenylalanine for serine increased affinity for IFNAR2 ∼4-fold and commensurately enhanced activation of STAT1, STAT3, and STAT5, transcription of a subset of interferon stimulated genes, and restriction of vesicular stomatitis virus infection in vitro. Structural modeling suggests that S27 of IFNα1 disrupts the IFNα:IFNAR2 hydrophobic interface that is otherwise stabilized by F27 and that replacing S27 with phenylalanine partially restores the hydrophobic surface. Disruption of the hydrophobic IFNα:IFNAR2 interface by the unique S27 of IFN α1 contributes to its low affinity and weak antiviral activity.

Interferon lambda protects the female reproductive tract against Zika virus infection

Although Zika virus (ZIKV) can be transmitted sexually and cause congenital birth defects, immune control mechanisms in the female reproductive tract (FRT) are not well characterized. Here we show that treatment of primary human vaginal and cervical epithelial cells with interferon (IFN)-α/β or IFN-λ induces host defense transcriptional signatures and inhibits ZIKV infection. We also assess the effects of IFNs on intravaginal infection of the FRT using ovariectomized mice treated with reproductive hormones. We find that mice receiving estradiol are protected against intravaginal ZIKV infection, independently of IFN-α/β or IFN-λ signaling. In contrast, mice lacking IFN-λ signaling sustain greater FRT infection when progesterone is administered. Exogenous IFN-λ treatment confers an antiviral effect when mice receive both estradiol and progesterone, but not progesterone alone. Our results identify a hormonal stage-dependent role for IFN-λ in controlling ZIKV infection in the FRT and suggest a path for minimizing sexual transmission of ZIKV in women.

Human interferon-ϵ and interferon-κ exhibit low potency and low affinity for cell-surface IFNAR and the poxvirus antagonist B18R

IFNϵ and IFNκ are interferons that induce microbial immunity at mucosal surfaces and in the skin. They are members of the type-I interferon (IFN) family, which consists of 16 different IFNs, that all signal through the common IFNAR1/IFNAR2 receptor complex. Although IFNϵ and IFNκ have unique expression and functional properties, their biophysical properties have not been extensively studied. In this report, we describe the expression, purification, and characterization of recombinant human IFNϵ and IFNκ. In cellular assays, IFNϵ and IFNκ exhibit ∼1000-fold lower potency than IFNα2 and IFNω. The reduced potency of IFNϵ and IFNκ are consistent with their weak affinity for the IFNAR2 receptor chain. Despite reduced IFNAR2-binding affinities, IFNϵ and IFNκ exhibit affinities for the IFNAR1 chain that are similar to other IFN subtypes. As observed for cellular IFNAR2 receptor, the poxvirus antagonist, B18R, also exhibits reduced affinity for IFNϵ and IFNκ, relative to the other IFNs. Taken together, our data suggest IFNϵ and IFNκ are specialized IFNs that have evolved to weakly bind to the IFNAR2 chain, which allows innate protection of the mucosa and skin and limits neutralization of IFNϵ and IFNκ biological activities by viral IFN antagonists.

The Sodium Sialic Acid Symporter From Staphylococcus aureus Has Altered Substrate Specificity

Mammalian cell surfaces are decorated with complex glycoconjugates that terminate with negatively charged sialic acids. Commensal and pathogenic bacteria can use host-derived sialic acids for a competitive advantage, but require a functional sialic acid transporter to import the sugar into the cell. This work investigates the sodium sialic acid symporter (SiaT) from Staphylococcus aureus (SaSiaT). We demonstrate that SaSiaT rescues an Escherichia coli strain lacking its endogenous sialic acid transporter when grown on the sialic acids N-acetylneuraminic acid (Neu5Ac) or N-glycolylneuraminic acid (Neu5Gc). We then develop an expression, purification and detergent solubilization system for SaSiaT and demonstrate that the protein is largely monodisperse in solution with a stable monomeric oligomeric state. Binding studies reveal that SaSiaT has a higher affinity for Neu5Gc over Neu5Ac, which was unexpected and is not seen in another SiaT homolog. We develop a homology model and use comparative sequence analyses to identify substitutions in the substrate-binding site of SaSiaT that may explain the altered specificity. SaSiaT is shown to be electrogenic, and transport is dependent upon more than one Na⁺ ion for every sialic acid molecule. A functional sialic acid transporter is essential for the uptake and utilization of sialic acid in a range of pathogenic bacteria, and developing new inhibitors that target these transporters is a valid mechanism for inhibiting bacterial growth. By demonstrating a route to functional recombinant SaSiaT, and developing the in vivo and in vitro assay systems, our work underpins the design of inhibitors to this transporter.

Interferon-associated therapies toward HIV control: The back and forth

Human immunodeficiency virus (HIV) induces a persistent and incurable infection. However, the combined antiretroviral treatment (cART) has markedly changed the evolution of the infection and transformed a deadly disease into a manageable chronic infection. Withdrawal of cART generally leads though to resumption of the viral replication. The eradication of the virus from its cellular and anatomical reservoirs remains a goal-to-achieve for a cure. In this context, developing novel therapies contributing to this aim are an important field of research. Type I IFN has antiviral activity, which, before the presence of efficient anti-HIV drugs, has led to the testing of IFN-based therapeutic strategies during the early years of the pandemic. A historical overview of the results and its limitations that were put into light are reviewed here. In addition, several lessons could be drawn. For instance, the efficacy of the IFN-I depends on the timing of its administration and the context. Thus, the persistence of an endogenous IFN-signature, such as that generally observed in viremic patients, seems to be associated with a lower efficacy of IFN. Based on the lessons from previous trials, and in the context of cART and research for a cure, type I Interferon has regained interest and novel therapeutic approaches are currently tested in combination with cART, some with disappointing, other with encouraging results with regard to a reduction in the size of the HIV reservoir and/or delays in viral rebound after cessation of cART. Additional strategies are currently developed in addition to improve the antiviral function of the IFN-I, by using for instance other IFN subtypes than IFN-Iα2. In parallel, the development of innovative strategies aimed at counteracting the excessive activation of the IFN-pathways have been continued and their results are reviewed here as well. Altogether, the use of IFN-I in anti-HIV therapies has gone through distinct phases and many lessons could be drawn. Novel combinations are currently be tested that might provide interesting results.