Comparative analysis of miRNA profile in human dendritic cells infected with respiratory syncytial virus and human metapneumovirus

Non-fatal outcomes of COVID-19 disease in pediatric organ transplantation associates with down-regulation of senescence pathways

This is a cross-sectional study examining kinetics and durability of immune response in children with solid organ transplants (SOTs) who had COVID-19 disease between November 2020 through June 2022, who were followed for 60-days at a single transplant center. Blood was collected between 1-14 (acute infection), and 15-60 days of a positive PCR (convalescence). SOT children with peripheral blood mononuclear cells (PBMC) cryopreserved before 2019 were non-infected controls (ctrls). PBMCs stimulated with 15-mer peptides from spike protein and anti-CD49d/anti-CD28. Testing done included mass cytometry, mi-RNA sequencing with confirmatory qPCR. 38 children formed the study cohort, 10 in the acute phase and 8 in the convalescence phase. 20 subjects were non-infected controls. Two subjects had severe disease. Subjects in the acute and convalescent phases were different subjects. The median age and tacrolimus level at blood draw was not significantly different. There was no death, and no subject was lost to follow-up. During acute infection CD57 expression was low in NKT, Th17 effector memory, memory Treg, CD4-CD8-, and γδT cells (p = 0.01, p = 0.04, p = 0.03, p = 0.03, p = 0.004 respectively). The frequencies of NK and Th2 effector memory cells increased (p = 0.01, p = 0.02) during acute infection. Non-switched memory B and CD8 central memory cell frequencies were decreased during acute infection (p = 0.02; p = 0.02), but the decrease in CD8 central memory cells did not persist. CD4-CD8- and CD14 monocyte frequencies increased during recovery (p = 0.03; p = 0.007). Our observations suggest down regulation of CD57 with absence of NK cell contraction protect against death from COVID-19 disease in children with SOTs.

Human Metapneumovirus-Induced Host microRNA Expression Impairs the Interferon Response in Macrophages and Epithelial Cells

Human metapneumovirus (HMPV) is a nonsegmented, single-stranded negative RNA virus and a member of the Pneumoviridae family. During HMPV infection, macrophages play a critical role in defending the respiratory epithelium by secreting large amounts of type I interferon (IFN). MicroRNAs (miRNAs) are small, noncoding, single-stranded RNAs that play an essential role in regulating gene expression during normal cellular homeostasis and disease by binding to specific mRNAs, thereby regulating at the transcriptional and post-transcriptional levels with a direct impact on the immune response and other cellular processes. However, the role of miRNAs in macrophages and respiratory viral infections remains largely unknown. Here, we characterized the susceptibility of THP-1-derived macrophages to HMPV infection and the effect of hsa-miR-4634 on these cells. Transfection of an miRNA mimic and inhibitor demonstrated that hsa-miR-4634 regulates the IFN response in HMPV-infected macrophages, suggesting that HMPV induces the expression of the miRNA as a subversion mechanism of the antiviral response. This effect was not limited to macrophages, as a similar effect was also observed in epithelial cells. Overall, our results demonstrate that hsa-miR-4634 is an important factor in regulating the IFN response in macrophages and epithelial cells during HMPV infection.

Potential of MicroRNAs As Biomarkers and Therapeutic Targets in Respiratory Viruses: A Literature Review

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression through recognition of cognate sequences and interference of transcriptional, translational, or epigenetic processes. Hundreds of miRNA genes have been found in diverse viruses, and many of these are phylogenetically conserved. Respiratory viruses are the most frequent causative agents of disease in humans, with a significant impact on morbidity and mortality worldwide. Recently, the role of miRNAs in respiratory viral gene regulation, as well as host gene regulation during disease progression, has become a field of interest. This review highlighted the importance of various miRNAs and their potential role in fighting with respiratory viruses as therapeutic molecules with a focus on COVID-19.

Interferon-Inducible LINC02605 Promotes Antiviral Innate Responses by Strengthening IRF3 Nuclear Translocation

Non-coding RNAs represent a class of important regulators in immune response. Previously, LINC02605 was identified as a candidate regulator in innate immune response by lncRNA microarray assays. In this study, we systematically analyzed the functions and the acting mechanisms of LINC02605 in antiviral innate immune response. LINC02605 was up-regulated by RNA virus, DNA virus, and type I IFNs in NF-κB and Jak-stat dependent manner. Overexpression of LINC02605 promotes RNA virus-induced type I interferon production and inhibited viral replication. Consistently, knockdown of LINC02605 resulted in reduced antiviral immune response and increased viral replication. Mechanistically, LINC02605 released the inhibition of hsa-miR-107 on the expression of phosphatase and tensin homolog (PTEN). By microRNA mimics and inhibitors, hsa-miR-107 was demonstrated to not only inhibit PTEN’s expression but also negatively regulate the antiviral immune response. Knockdown of LINC02605 led to the reduction of PTEN expression both in mRNA and protein levels. Overexpression of LINC02605 had an opposite impact. Moreover, LINC02605 attenuated the serine 97 phosphorylation level of interferon regulatory factor 3 (IRF3) by promoting PTEN expression. Nucleoplasmic fragmentation assay showed that knocking down LINC02605 inhibited the nuclear translocation of IRF3, rendering the host cells more susceptible to viral invasion, while overexpression showed opposite effects. Therefore, LINC02605 is an induced lncRNA by viral infection and plays a positive feedback in antiviral immune response through modulating the nuclear translocation of IRF3.

The Importance of miRNA Identification During Respiratory Viral Infections

The expression of small non-coding RNA MicroRNAs (miRNAs) during respiratory viral infections is of critical importance as they are implicated in the viral replication, immune responses and severity of disease pathogenesis. Respiratory viral infections have an extensive impact on human health across the globe. For that is essential to understand the factors that regulate the host response against infections. The differential miRNA pattern induced by respiratory viruses has been reported, including include influenza A virus (IAV), human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), adenovirus (AdV), and more recently, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. In this commentary, we highlight the importance of miRNAs identification and the contribution of these molecules in the modulation of the immune response through the upregulation and downregulation of miRNAs expression in different immune and non-immune cells.

miRNAs and Leukotrienes in Respiratory Syncytial Virus Infection

MicroRNAs (miRNAs) are small, non-coding RNAs that regulate posttranscription by binding to 3'-untranslated regions of target mRNAs. Recent functional studies have elucidated mechanisms that miRNAs regulate leukotriene synthesis by perturbing arachidonic acid metabolism. Both microarrays and high-throughput sequencing revealed distinct differential expression of miRNAs in children with respiratory syncytial virus (RSV) infection compared with healthy controls. Abnormal miRNA expression may contribute to higher leukotriene levels, which is associated with airway hyperreactivity. Targeting miRNAs may benefit to restore the homeostasis of inflammatory reaction and provide new strategies to alleviate airway hyperreactivity induced by RSV. In this article, we provide an overview of the current knowledge about miRNAs modulating leukotrienes through regulation of arachidonic acid metabolism with a special focus on miRNAs aberrantly expressed in children with RSV infection.

The expression profile and bioinformatics analysis of microRNAs in human bronchial epithelial cells treated by beryllium sulfate

Beryllium and its compounds are systemic toxicants that mainly accumulate in the lungs. As a regulator of gene expression, microRNAs (miRNAs) were involved in some lung diseases. This study aimed to analyze the levels of some inflammatory cytokine and the differential expressions of miRNAs in human bronchial epithelial cells (16HBE) induced by beryllium sulfate (BeSO₄ ) and to further explore the biological functions of differentially expressed miRNAs. The profile of miRNAs in 16HBE cells was detected using the high-throughput sequencing between the control groups (n = 3) and the 150 μmol/L of BeSO₄ -treated groups (n = 3). Bioinformatics analysis of differentially expressed miRNAs was performed, including the prediction of target genes, Gene Ontology (GO) analysis, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Quantitative real-time polymerase chain reaction (qRT-PCR) was applied to verify some damage-related miRNAs. We found that BeSO₄ can increase the levels of some inflammatory cytokine such as interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), interferon-γ (IFN-γ), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). And BeSO₄ altered miRNAs expression of 16HBE cells and a total of 179 differentially expressed miRNAs were identified, including 88 upregulated miRNAs and 91 downregulated miRNAs. The target genes predicted by 28 dysregulated miRNAs were mainly involved in the transcription regulation, signal transduction, MAPK, and VEGF signaling pathway. The qRT-PCR verification results were consistent with the sequencing results. miRNA expression profiling in 16HBE cells exposed to BeSO₄ provides new insights into the toxicity mechanism of beryllium exposure.

The emerging role of microRNAs in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection

The novel coronavirus disease 2019 (COVID-19) pandemic has imposed significant public health problems for the human populations worldwide after the 1918 influenza A virus (IVA) (H1N1) pandemic. Although numerous efforts have been made to unravel the mechanisms underlying the coronavirus, a notable gap remains in our perception of the COVID-19 pathogenesis. The innate and adaptive immune systems have a pivotal role in the fate of viral infections, such as COVID-19 pandemic. MicroRNAs (miRNAs) are known as short noncoding RNA molecules and appear as indispensable governors of almost any cellular means. Several lines of evidence demonstrate that miRNAs participate in essential mechanisms of cell biology, regulation of the immune system, and the onset and progression of numerous types of disorders. The immune responses to viral respiratory infections (VRIs), including influenza virus (IV), respiratory syncytial virus (RSV), and rhinovirus (RV), are correlated with the ectopic expression of miRNAs. Alterations of the miRNA expression in epithelial cells may contribute to the pathogenesis of chronic and acute airway infections. Hence, analyzing the role of these types of nucleotides in antiviral immune responses and the characterization of miRNA target genes might contribute to understanding the mechanisms of the interplay between the host and viruses, and in the future, potentially result in discovering therapeutic strategies for the prevention and treatment of acute COVID-19 infection. In this article, we present a general review of current studies concerning the function of miRNAs in different VRIs, particularly in coronavirus infection, and address all available therapeutic prospects to mitigate the burden of viral infections.

miR-4634 augments the anti-tumor effects of RAD001 and associates well with clinical prognosis of non-small cell lung cancer

MicroRNA (miRNA) is involved in the physiological and pathological processes of various malignancies. In this study, miRNA microarray analysis showed that miR-4634 levels in A549 cells increased significantly after everolimus (RAD001) treatment. Decreased expression of miR-4634 was also found in non-small-cell lung carcinoma (NSCLC) cell lines and patients’ tumors by qPCR. Additionally, a combination of miR-4634 and RAD001 exerted synergistic antitumor efficacy by inhibiting cell proliferation, migration, and colony formation. High expression of miR-4634 was significantly more common in non-cancerous lung tissue than adenocarcinoma or squamous cell carcinoma tissue (72.8%, 45.7%, and 50.9%, respectively; P < 0.001). Furthermore, high expression of miR-4634 was found to be more frequent in patients without lymph node metastasis (P = 0.037) by in-situ hybridization. Importantly, through univariate and multivariate analysis, high miR-4634 expression was associated with better prognosis of NSCLC patients. In conclusion, miR-4634 may act as a tumor suppressor in NSCLC, and to augment the efficacy of RAD001, co-treatment of miR-4634 and RAD001 might be a potential mTOR-targeted cancer therapy strategy for NSCLC patients. High expression of miR-4634 could be an independent good prognostic biomarker for NSCLC.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Cell-Mediated Responses to Human Metapneumovirus Infection

Viruses are the most common cause of acute respiratory tract infections (ARTI). Human metapneumovirus (hMPV) frequently causes viral pneumonia which can become life-threatening if the virus spreads to the lungs. Even though hMPV was only isolated in 2001, this negative-stranded RNA virus has probably been circulating in the human population for many decades. Interestingly, almost all adults have serologic evidence of hMPV infection. A well-established host immune response is evoked when hMPV infection occurs. However, the virus has evolved to circumvent and even exploit the host immune response. Further, infection with hMPV induces a weak memory response, and re-infections during life are common. In this review, we provide a comprehensive overview of the different cell types involved in the immune response in order to better understand the immunopathology induced by hMPV. Such knowledge may contribute to the development of vaccines and therapeutics directed against hMPV.

Identification of miRNA-mRNA Crosstalk in Respiratory Syncytial Virus- (RSV-) Associated Pediatric Pneumonia through Integrated miRNAome and Transcriptome Analysis

Respiratory syncytial virus (RSV) is the most common respiratory virus and is associated with pediatric pneumonia, causing bronchiolitis and significant mortality in infants and young children. MicroRNAs (miRNAs) are endogenous noncoding small RNAs that function in gene regulation and are associated with host immune response and disease progression. In the present study, we profiled the global transcriptome and miRNAome of whole blood samples from children with mild or severe RSV-associated pneumonia, aiming to identify the potential biomarkers and investigate the molecular mechanisms of severe RSV-associated pediatric pneumonia. We found that expression profiles of whole blood microRNAs and mRNAs were altered and distinctly different in children with severe RSV-associated pneumonia. In particular, the four most significantly upregulated miRNAs in children with severe RSV-associated pneumonia were hsa-miR-1271-5p, hsa-miR-10a-3p, hsa-miR-125b-5p, and hsa-miR-30b-3p. The severe RSV-associated pneumonia-specific differentially expressed miRNA target interaction network was also contrasted. These target genes were further analyzed with Gene Ontology enrichment analysis. We found that most of the target genes were involved in inflammatory and immune responses, including the NF-κB signaling pathway, the MAPK signaling pathway, and T cell receptor signaling. Our findings will contribute to the identification of biomarkers and new drug design strategies to treat severe RSV-associated pediatric pneumonia.

Advances in laboratory assays for detecting human metapneumovirus

Human metapneumovirus (HMPV) is one of the major causes of acute respiratory tract infection (ARI) and shows high morbidity and mortality, particularly in children and immunocompromised patients. Various methods for detecting HMPV have been developed and applied in clinical laboratories. When reviewing the literature, we found that polymerase chain reaction (PCR)-based assays have been most frequently and consistently used to detect HMPV. The most commonly used method was multiplex reverse transcriptase-PCR (RT-PCR; 57.4%), followed by real-time RT-PCR (38.3%). Multiplex RT-PCR became the more popular method in 2011-2019 (69.7%), in contrast to 2001-2009 (28.6%). The advent of multiplex PCR in detecting broader viral pathogens in one run and coinfected viruses influenced the change in user preference. Further, newly developed microarray technologies and ionization mass spectrometry were introduced in 2011-2019. Viral culture (including shell vial assays) and fluorescent immunoassays (with or without culture) were once the mainstays. However, the percentage of studies employing culture and fluorescent immunoassays decreased from 21.4% in 2001-2010 to 15.2% in 2011-2019. Meanwhile, the use of PCR-based methods of HMPV detection increased from 78.6% in 2001-2010 to 84.8% in 2011-2019. The increase in PCR-based methods might have occurred because PCR methods demonstrated better diagnostic performance, shorter hands-on and run times, less hazards to laboratory personnel, and more reliable results than traditional methods. When using these assays, it is important to acquire a comprehensive understanding of the principles, advantages, disadvantages, and precautions for data interpretation. In the future, the combination of nanotechnology and advanced genetic platforms such as next-generation sequencing will benefit patients with HMPV infection by facilitating efficient therapeutic intervention. Analytical and clinical validation are required before using new techniques in clinical laboratories.

Non-Coding RNAs and Their Role in Respiratory Syncytial Virus (RSV) and Human Metapneumovirus (hMPV) Infections

Recent high-throughput sequencing revealed that only 2% of the transcribed human genome codes for proteins, while the majority of transcriptional products are non-coding RNAs (ncRNAs). Herein, we review the current knowledge regarding ncRNAs, both host- and virus-derived, and their role in respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) infections. RSV is known as the most common cause of lower respiratory tract infection (LRTI) in children, while hMPV is also a significant contributor to LRTI in the pediatrics population. Although RSV and hMPV are close members, belonging to the Pneumoviridae family, they induce distinct changes in the ncRNA profile. Several types of host ncRNAs, including long ncRNA (lncRNA), microRNAs (miRNAs), and transfer RNA (tRNA)-derived RNA fragments (tRFs), are involved as playing roles in RSV and/or hMPV infection. Given the importance of ncRNAs in regulating the expression and functions of genes and proteins, comprehensively understanding the roles of ncRNAs in RSV/hMPV infection could shed light upon the disease mechanisms of RSV and hMPV, potentially providing insights into the development of prevention strategies and antiviral therapy. The presence of viral-derived RNAs and the potential of using ncRNAs as diagnostic biomarkers are also discussed in this review.

Interactome networks between the human respiratory syncytial virus (HRSV), the human metapneumovirus (ΗMPV), and their host: In silico investigation and comparative functional enrichment analysis

BACKGROUND AND OBJECTIVES

Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are leading causes of upper and lower respiratory tract infections in non-immunocompetent subjects, yet the mechanisms by which they induce their pathogenicity differ significantly and remain elusive. In this study we aimed at identifying the gene interaction networks between the HRSV, HMPV respiratory pathogens and their host along with the different cell-signaling pathways associated with the above interactomes.

MATERIALS AND METHODS

The Viruses STRING database (http://viruses.string-db.org/) was used for the identification of the host-viruses interaction networks. The two lists of the predicted functional partners were entered in the FunRich tool (http://www.funrich.org) for the construction of the Venn diagram and the comparative Funcional Enrichment Analysis (FEA) with respect to biological pathways. The sets of the common and unique human genes identified in the two networks were also analyzed. The computational predictions regarding the shared human genes in the host-HRSV and the host-HMPV interactomes were further evaluated via the analysis of the GSE111732 dataset. miRNA transcriptomics data were mapped to gene targets using the miRNomics pipeline of the GeneTrail2 database (https://genetrail2.bioinf.uni-sb.de/).

RESULTS

Eleven out of twenty predicted human genes were common in the two interactomes (TLR4, SOCS3, SFXN1, AKT1, SFXN3, LY96, SFXN2, SOCS7, CISH, SOCS6, SOCS1). FEA of these common genes identified the kit receptor and the GH receptor signaling pathways as the most significantly enriched annotations. The remaining nine genes of the host-HRSV and the host-HMPV interaction networks were the IFIH1, DDX58, NCL, IRF3, STAT2, HSPA4, CD209, KLF6, CHKA and the MYD88, SOCS4, SOCS2, SOCS5 AKT2, AKT3, SFXN4, SFXN5 and TLR3 respectively. Distinct cell-signaling pathways were enriched per interactome. The comparative FEA highlighted the association of the host-HRSV functional partners with the negative regulation of RIG-I/MDA5 signaling. The analysis with respect to miRNAs mapping to gene targets of the GSE111732 dataset indicated that nine out of the eleven common host genes are either enriched or depleted in the sample sets (HRSV or HMPV infected) as compared with the reference set (non-infected), although with no significant scores.

CONCLUSIONS

We have identified both shared and unique host genes as members of the HRSV and HMPV interaction networks. The disparate human genes likely contribute to distinct responses in airway epithelial cells.

Determining Immune and miRNA Biomarkers Related to Respiratory Syncytial Virus (RSV) Vaccine Types

Respiratory Syncytial Virus (RSV) causes serious respiratory tract illness and substantial morbidity and some mortality in populations at the extremes of age, i.e., infants, young children, and the elderly. To date, RSV vaccine development has been unsuccessful, a feature linked to the lack of biomarkers available to assess the safety and efficacy of RSV vaccine candidates. We examined microRNAs (miR) as potential biomarkers for different types of RSV vaccine candidates. In this study, mice were vaccinated with a live attenuated RSV candidate that lacks the small hydrophobic (SH) and attachment (G) proteins (CP52), an RSV G protein microparticle (GA2-MP) vaccine, a formalin-inactivated RSV (FI-RSV) vaccine or were mock-treated. Several immunological endpoints and miR expression profiles were determined in mouse serum and bronchoalveolar lavage (BAL) following vaccine priming, boost, and RSV challenge. We identified miRs that were linked with immunological parameters of disease and protection. We show that miRs are potential biomarkers providing valuable insights for vaccine development.

Silver, titanium dioxide, and zinc oxide nanoparticles trigger miRNA/isomiR expression changes in THP-1 cells that are proportional to their health hazard potential

After over a decade of nanosafety research, it is indisputable that the vast majority of nano-sized particles induce a plethora of adverse cellular responses - the severity of which is linked to the material's physicochemical properties. Differentiated THP-1 cells were previously exposed for 6 h and 24 h to silver, titanium dioxide, and zinc oxide nanoparticles at the maximum molar concentration at which no more than 15% cellular cytotoxicity was observed. All three nanoparticles differed in extent of induction of biological pathways corresponding to immune response signaling and metal ion homeostasis. In this study, we integrated gene and miRNA expression profiles from the same cells to propose miRNA biomarkers of adverse exposure to metal-based nanoparticles. We employed RNA sequencing together with a quantitative strategy that also enables analysis of the overlooked repertoire of length and sequence miRNA variants called isomiRs. Whilst only modest changes in expression were observed within the first 6 h of exposure, the miRNA/isomiR (miR) profiles of each nanoparticle were unique. Via canonical correlation and pathway enrichment analyses, we identified a co-regulated miR-mRNA cluster, predicted to be highly relevant for cellular response to metal ion homeostasis. These miRs were annotated to be canonical or variant isoforms of hsa-miR-142-5p, -342-3p, -5100, -6087, -6894-3p, and -7704. Hsa-miR-5100 was differentially expressed in response to each nanoparticle in both the 6 h and 24 h exposures. Taken together, this co-regulated miR-mRNA cluster could represent potential biomarkers of sub-toxic metal-based nanoparticle exposure.

Immune-Modulation by the Human Respiratory Syncytial Virus: Focus on Dendritic Cells

The human respiratory syncytial virus (hRSV) is the leading cause of pneumonia in infants and produces a significant burden in the elderly. It can also infect and produce disease in otherwise healthy adults and recurrently infect those previously exposed to the virus. Importantly, recurrent infections are not necessarily a consequence of antigenic variability, as described for other respiratory viruses, but most likely due to the capacity of this virus to interfere with the host's immune response and the establishment of a protective and long-lasting immunity. Although some genes encoded by hRSV are known to have a direct participation in immune evasion, it seems that repeated infection is mainly given by its capacity to modulate immune components in such a way to promote non-optimal antiviral responses in the host. Importantly, hRSV is known to interfere with dendritic cell (DC) function, which are key cells involved in establishing and regulating protective virus-specific immunity. Notably, hRSV infects DCs, alters their maturation, migration to lymph nodes and their capacity to activate virus-specific T cells, which likely impacts the host antiviral response against this virus. Here, we review and discuss the most important and recent findings related to DC modulation by hRSV, which might be at the basis of recurrent infections in previously infected individuals and hRSV-induced disease. A focus on the interaction between DCs and hRSV will likely contribute to the development of effective prophylactic and antiviral strategies against this virus.

Human Metapneumovirus: Mechanisms and Molecular Targets Used by the Virus to Avoid the Immune System

Human metapneumovirus (hMPV) is a respiratory virus, first reported the year 2001. Since then, it has been described as one of the main etiological agents that causes acute lower respiratory tract infections (ALRTIs), which is characterized by symptoms such as bronchiolitis, wheezing and coughing. Susceptible population to hMPV-infection includes newborn, children, elderly and immunocompromised individuals. This viral agent is a negative-sense, single-stranded RNA enveloped virus, that belongs to the Pneumoviridae family and Metapneumovirus genus. Early reports—previous to 2001—state several cases of respiratory illness without clear identification of the responsible pathogen, which could be related to hMPV. Despite the similarities of hMPV with several other viruses, such as the human respiratory syncytial virus or influenza virus, mechanisms used by hMPV to avoid the host immune system are still unclear. In fact, evidence indicates that hMPV induces a poor innate immune response, thereby affecting the adaptive immunity. Among these mechanisms, is the promotion of an anergic state in T cells, instead of an effective polarization or activation, which could be induced by low levels of cytokine secretion. Further, the evidences support the notion that hMPV interferes with several pattern recognition receptors (PRRs) and cell signaling pathways triggered by interferon-associated genes. However, these mechanisms reported in hMPV are not like the ones reported for hRSV, as the latter has two non-structural proteins that are able to inhibit these pathways. Several reports suggest that viral glycoproteins, such as G and SH, could play immune-modulator roles during infection. In this work, we discuss the state of the art regarding the mechanisms that underlie the poor immunity elicited by hMPV. Importantly, these mechanisms will be compared with those elicited by other common respiratory viruses.

Interferon-Mediated Response to Human Metapneumovirus Infection

Human metapneumovirus (HMPV) is one of the leading causes of respiratory diseases in infants and children worldwide. Although this pathogen infects mainly young children, elderly and immunocompromised people can be also seriously affected. To date, there is no commercial vaccine available against it. Upon HMPV infection, the host innate arm of defense produces interferons (IFNs), which are critical for limiting HMPV replication. In this review, we offer an updated landscape of the HMPV mediated-IFN response in different models as well as some of the defense tactics employed by the virus to circumvent IFN response.