Siglec-1 inhibits RSV-induced interferon gamma production by adult T cells in contrast to newborn T cells

Reshaping Our Knowledge: Advancements in Understanding the Immune Response to Human Respiratory Syncytial Virus

Human respiratory syncytial virus (hRSV) is a significant cause of respiratory tract infections, particularly in young children and older adults. In this review, we aimed to comprehensively summarize what is known about the immune response to hRSV infection. We described the innate and adaptive immune components involved, including the recognition of RSV, the inflammatory response, the role of natural killer (NK) cells, antigen presentation, T cell response, and antibody production. Understanding the complex immune response to hRSV infection is crucial for developing effective interventions against this significant respiratory pathogen. Further investigations into the immune memory generated by hRSV infection and the development of strategies to enhance immune responses may hold promise for the prevention and management of hRSV-associated diseases.

CD169 expression on monocytes as a marker for assessing type I interferon status in pediatric inflammatory diseases

BACKGROUND

Evaluation of type I interferons (IFNs) in inflammatory or autoimmune diseases is challenging because of their rapid clearance in peripheral blood. The IFN gene expression signature has recently been used to evaluate the IFN status; however, this is often a labor-intensive and time-consuming procedure. Therefore, we assessed the feasibility of measuring expression of an IFN-inducible protein, CD169 (Siglec-1), on monocytes and circulating levels of soluble CD169 as alternative markers for type I IFN status in various pediatric inflammatory diseases.

METHODS

Data from flow cytometric analysis of surface CD169 on monocytes and an enzyme-linked immunosorbent assay of soluble CD169 in peripheral blood were compared with serum IFN-α levels in 8 patients with viral infections, 5 with bacterial infections, 10 with systemic lupus erythematosus (SLE), 5 with Kikuchi-Fujimoto disease (KFD), 7 with Kawasaki disease (KD), and 8 with inflammatory bowel disease (IBD), and in 8 healthy controls.

RESULTS

Surface CD169 expression was detected mainly on CD14⁺ monocytes and was significantly increased in patients with viral infections, SLE, and KFD, but not in patients with bacterial infections, KD, and IBD. There were similar trends for circulating soluble CD169; however, there was a significant increase only in patients with viral infections. Surface CD169 levels were significantly correlated with serum levels of IFN-α and soluble CD169.

CONCLUSION

Analysis of CD169 expression on CD14⁺ monocytes may be useful for rapid assessment of type I IFN status for differentiation of pediatric inflammatory diseases from type 1 IFN-mediated diseases.

The role of sialic acid-binding immunoglobulin-like-lectin-1 (siglec-1) in immunology and infectious disease

Siglec-1, also known as Sialoadhesin (Sn) and CD169 is highly conserved among vertebrates and with 17 immunoglobulin-like domains is Siglec-1 the largest member of the Siglec family. Expression of Siglec-1 is found primarily on dendritic cells (DCs), macrophages and interferon induced monocyte. The structure of Siglec-1 is unique among siglecs and its function as a receptor is also different compared to other receptors in this class as it contains the most extracellular domains out of all the siglecs. However, the ability of Siglec-1 to internalize antigens and to pass them on to lymphocytes by allowing dendritic cells and macrophages to act as antigen presenting cells, is the main reason that has granted Siglec-1's key role in multiple human disease states including atherosclerosis, coronary artery disease, autoimmune diseases, cell-cell signaling, immunology, and more importantly bacterial and viral infections. Enveloped viruses for example have been shown to manipulate Siglec-1 to increase their virulence by binding to sialic acids present on the virus glycoproteins allowing them to spread or evade immune response. Siglec-1 mediates dissemination of HIV-1 in activated tissues enhancing viral spread via infection of DC/T-cell synapses. Overall, the ability of Siglec-1 to bind a variety of target cells within the immune system such as erythrocytes, B-cells, CD8+ granulocytes and NK cells, highlights that Siglec-1 is a unique player in these essential processes.

SARS-CoV-2 spike protein induces a differential monocyte activation that may contribute to age bias in COVID-19 severity

A strong bias related to age is observed in COVID-19 patients with pediatric subjects developing a milder disease than adults. We hypothesized that a specific SARS-CoV-2 effect conjugated with preexisting differences in the immune systems may explain this. Using flow cytometry, we investigated basal immune differences in a cohort consisting of 16 non-infected young and 16 aged individuals and further leveraged an in vitro whole blood model of SARS-CoV-2 infection so that functional differences could be mined as well. In short, blood diluted in culture media was incubated 5 or 24 h with the trimeric spike protein or controls. Following unsupervised analysis, we first confirmed that the immune lymphoid and myeloid systems in adults are less efficient and prone to develop higher inflammation than those in children. We notably identified in adults a higher CD43 lymphocyte expression, known for its potentially inhibitory role. The spike protein induced different responses between adults and children, notably a higher increase of inflammatory markers together with lower monocyte and B cell activation in adults. Interestingly, CD169, a CD43 ligand overexpressed in COVID-19 patients, was confirmed to be strongly modulated by the spike protein. In conclusion, the spike protein exacerbated the preexisting lower immune responsiveness and higher inflammatory potential in adults. Altogether, some of the markers identified may explain the marked age bias and be predictive of severity.

Alveolar macrophages and airway hyperresponsiveness associated with respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a ubiquitous pathogen of viral bronchiolitis and pneumonia in children younger than 2 years of age, which is closely associated with recurrent wheezing and airway hyperresponsiveness (AHR). Alveolar macrophages (AMs) located on the surface of the alveoli cavity are the important innate immune barrier in the respiratory tract. AMs are recognized as recruited airspace macrophages (RecAMs) and resident airspace macrophages (RAMs) based on their origins and roaming traits. AMs are polarized in the case of RSV infection, forming two macrophage phenotypes termed as M1-like and M2-like macrophages. Both M1 macrophages and M2 macrophages are involved in the modulation of inflammatory responses, among which M1 macrophages are capable of pro-inflammatory responses and M2 macrophages are capable of anti-proinflammatory responses and repair damaged tissues in the acute and convalescent phases of RSV infection. Polarized AMs affect disease progression through the alteration of immune cell surface phenotypes as well as participate in the regulation of T lymphocyte differentiation and the type of inflammatory response, which are closely associated with long-term AHR. In recent years, some progress have been made in the regulatory mechanism of AM polarization caused by RSV infection, which participates in acute respiratory inflammatory response and mediating AHR in infants. Here we summarized the role of RSV-infection-mediated AM polarization associated with AHR in infants.

Myeloid CD169/Siglec1: An immunoregulatory biomarker in viral disease

CD169, also known as Siglec1 or Sialoadhesin (Sn), is a surface adhesion molecule on human myeloid cells. Being part of the Siglec family, it acts as a receptor for sialylated molecular structures, which are found among various pathogenic and non-pathogenic ligands. Recent data suggest that CD169 may represent a promising new biomarker in acute respiratory and non-respiratory viral infections, such as SARS-CoV-2, Respiratory syncytial virus (RSV) and Human immunodeficiency virus (HIV). Therein lies a great potential to sufficiently differentiate viral from bacterial infection, which has been an incessant challenge in the clinical management of infectious disease. CD169 equips myeloid cells with functions, reaching far beyond pathogen elimination. In fact, CD169 seems to crosslink innate and adaptive immunity by antigen presentation and consecutive pathogen elimination, embodying a substantial pillar of immunoregulation. Yet, our knowledge about the kinetics, mechanisms of induction, signaling pathways and its precise role in host-pathogen interaction remains largely obscure. In this review, we describe the role of CD169 as a potentially novel diagnostic biomarker for respiratory viral infection by evaluating its strengths and weaknesses and considering host factors that are involved in pathogenesis of virus infection. Finally, this brief review aims to point out shortcomings of available evidence, thus, guiding future work revolving the topic.

A rapid, easy, and scalable whole blood monocyte CD169 assay for outpatient screening during SARS-CoV-2 outbreak, and potentially other emerging disease outbreaks

Objective

The COVID-19 corona virus disease outbreak is globally challenging health systems and societies. Its diagnosis relies on molecular methods, with drawbacks revealed by mass screening. Upregulation of neutrophil CD64 or monocyte CD169 has been abundantly reported as markers of bacterial or acute viral infection, respectively. We evaluated the sensitivity of an easy, one-step whole blood flow cytometry assay to measure these markers within 10 min, as a potential screening test for COVID-19 patients.

Methods

Patients (n = 177) with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were tested on 10 µL blood and results were compared with reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR).

Results

We observed 98% and 100% sensitivity in early-stage (n = 52) and asymptomatic patients (n = 9), respectively. Late-stage patients, who presented for a second control RT-qPCR, were negative for both assays in most cases. Conversely, neutrophil CD64 expression was unchanged in 75% of cases, without significant differences between groups.

Conclusion

Monocyte CD169 evaluation was highly sensitive for detecting SARS-CoV-2 infection in first-presentation patients; and it returns to basal level upon infection clearance. The potential ease of fingerprick collection, minimal time-to-result, and low cost rank this biomarker measurement as a potential viral disease screening tool, including COVID-19. When the virus prevalence in the tested population is usually low (1%-10%), such an approach could increase the testing capacity 10 to 100-fold, with the same limited molecular testing resources, which could focus on confirmation purposes only.

Meta-Analysis of Whole Blood Transcriptome Datasets Characterizes the Immune Response of Respiratory Syncytial Virus Infection in Children

Respiratory syncytial virus (RSV) is the most common and critical viral pathogen causing acute lower respiratory tract infection in infants and young children and has a huge disease burden worldwide. At present, there are many studies on RSV transcriptomics exploring the mechanism of disease, but different studies show different gene expression patterns and results due to different sample collection platforms and data analysis strategies. A meta-analysis was performed on eight whole blood transcriptome datasets containing 436 children with acute RSV infection and 241 healthy children. A total of 319 differentially expressed genes (DEGs) (P value <0.0001) were identified in a meta-analysis using a random effect model. Functional enrichment analysis showed that several pathways related to immunity were significantly altered, including the “chemokine signaling pathway”, “natural killer cell mediated cytotoxicity” and “cytokine–cytokine receptor interaction”. Immune cell type analysis showed that the proportion of neutrophils in most RSV-infected children was higher than that in healthy children. These immune characteristics may help to provide new insights into RSV infection in children.

Association between TNF-α and IFN-γ levels and severity of acute viral bronchiolitis

Acute bronchiolitis caused by the respiratory syncytial virus triggers an inflammatory response with the production and release of several pro-inflammatory cytokines. Evidence suggests that their levels are associated with the severity of the infection. This systematic review and meta-analysis aim to assess whether the levels of TNF-α and IFN-γ are associated with the severity of acute viral bronchiolitis. We searched MEDLINE libraries (via PUBMED), EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), Scientific Electronic Library Online (SciELO), Latin American Caribbean Health Sciences Literature (LILACS), Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science, and the gray literature through April 2020. Random effect models were used for general and subgroup analysis. In total, six studies were included with a total of 744 participants. The mean TNF-α levels between the severe group did not differ from the control group 0.14 (95% CI: -0.53 to 0.82, I² = 91%, p < 0.01); the heterogeneity was high. The results remained insignificant when the analyses were performed including only studies with high quality 0.25 (95% CI: -0.46 to 0.96, I² = 92%, p < 0.01) I² = 95%, p = 0.815), when TNF-α was nasal 0.60 (95% CI: -0.49 to 1.69), I² = 94%, p < 0.01), or serum -0.08 (95% CI: -0.48 to 0.31), I² = 29%, p = 0.24). In the analysis of studies measuring IFN-γ, there was also no significance of -0.67 (95% CI: -1.56 to 0.22, I² = 76%, p = 0.04). In conclusion, this meta-analysis suggests that the most severe patients do not have different mean TNF-α and IFN-γ values ​than patients with mild disease, but the heterogeneity of the studies was high. Supplemental data for this article is available online at https://doi.org/10.1080/08830185.2021.1889534.

An OMICs based meta-analysis to support infection state stratification

MOTIVATION

A fundamental problem for disease treatment is that while antibiotics are a powerful counter to bacteria, they are ineffective against viruses. Often, bacterial and viral infections are confused due to their similar symptoms and lack of rapid diagnostics. With many clinicians relying primarily on symptoms for diagnosis, overuse and misuse of modern antibiotics are rife, contributing to the growing pool of antibiotic resistance. To ensure an individual receives optimal treatment given their disease state and to reduce over-prescription of antibiotics, the host response can in theory be measured quickly to distinguish between the two states. To establish a predictive biomarker panel of disease state (viral/bacterial/no-infection) we conducted a meta-analysis of human blood infection studies using Machine Learning (ML).

RESULTS

We focused on publicly available gene expression data from two widely used platforms, Affymetrix and Illumina microarrays as they represented a significant proportion of the available data. We were able to develop multi-class models with high accuracies with our best model predicting 93% of bacterial and 89% viral samples correctly. To compare the selected features in each of the different technologies, we reverse engineered the underlying molecular regulatory network and explored the neighbourhood of the selected features. The networks highlighted that although on the gene-level the models differed, they contained genes from the same areas of the network. Specifically, this convergence was to pathways including the Type I interferon Signalling Pathway, Chemotaxis, Apoptotic Processes, and Inflammatory/Innate Response.

AVAILABILITY

Data and code are available on the Gene Expression Omnibus and github.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

CD169 and CD64 could help differentiate bacterial from CoVID-19 or other viral infections in the Emergency Department

The identification of a bacterial, viral, or even noninfectious cause is essential in the management of febrile syndrome in the emergency department (ED), especially in epidemic contexts such as flu or CoVID-19. The aim was to assess discriminative performances of two biomarkers, CD64 on neutrophils (nCD64) and CD169 on monocytes (mCD169), using a new flow cytometry procedure, in patients presenting with fever to the ED during epidemics. Eighty five adult patients presenting with potential infection were included during the 2019 flu season in the ED of La Timone Hospital. They were divided into four diagnostic outcomes according to their clinical records: no-infection, bacterial infection, viral infection and co-infection. Seventy six patients with confirmed SARS-CoV-2 infection were also compared to 48 healthy volunteers. For the first cohort, 38 (45%) patients were diagnosed with bacterial infections, 11 (13%) with viral infections and 29 (34%) with co-infections. mCD169 was elevated in patients with viral infections, with a majority of Flu A virus or Respiratory Syncytial Virus, while nCD64 was elevated in subjects with bacterial infections, with a majority of Streptococcus pneumoniae and Escherichia coli. nCD64 and mCD169 showed 90% and 80% sensitivity, and 78% and 91% specificity, respectively, for identifying patients with bacterial or viral infections. When studied in a second cohort, mCD169 was elevated in 95% of patients with SARS-CoV-2 infections and remained at normal level in 100% of healthy volunteers. nCD64 and mCD169 have potential for accurately distinguishing bacterial and acute viral infections. Combined in an easy and rapid flow cytometry procedure, they constitute a potential improvement for infection management in the ED, and could even help for triage of patients during emerging epidemics.

Functions of CD169 positive macrophages in human diseases (Review)

CD169⁺ macrophages are a unique type of macrophage subset that differ from M1 and M2 macrophages. CD169⁺ macrophages are present in multiple tissues and organs throughout the body and are primarily expressed in secondary lymphoid organs. These cells are primarily divided across three locations in secondary lymphoid organs: The metallophilic marginal zone of the spleen, the subcapsular sinus and the medulla of the lymph nodes. Due to their unique location distribution in vivo and the presence of the CD169 molecule on their surfaces, CD169⁺ macrophages are reported to serve important roles in several processes, such as phagocytosis, antigen presentation, immune tolerance, viral infection and inflammatory responses. At the same time, it has been reported that CD169⁺ macrophages may also serve an important role in anti-tumour immunity. The present review focuses on the research progress surrounding the function of CD169⁺ macrophages in a variety of diseases, such as viral infection, autoimmune diseases and tumours.

Norovirus Replication in Human Intestinal Epithelial Cells Is Restricted by the Interferon-Induced JAK/STAT Signaling Pathway and RNA Polymerase II-Mediated Transcriptional Responses

Human noroviruses (HuNoV) are a leading cause of viral gastroenteritis worldwide and a significant cause of morbidity and mortality in all age groups. The recent finding that HuNoV can be propagated in B cells and mucosa-derived intestinal epithelial organoids (IEOs) has transformed our ability to dissect the life cycle of noroviruses. Using transcriptome sequencing (RNA-Seq) of HuNoV-infected intestinal epithelial cells (IECs), we have found that replication of HuNoV in IECs results in interferon (IFN)-induced transcriptional responses and that HuNoV replication in IECs is sensitive to IFN. This contrasts with previous studies that suggested that the innate immune response may play no role in the restriction of HuNoV replication in immortalized cells. We demonstrated that inhibition of Janus kinase 1 (JAK1)/JAK2 enhanced HuNoV replication in IECs. Surprisingly, targeted inhibition of cellular RNA polymerase II-mediated transcription was not detrimental to HuNoV replication but instead enhanced replication to a greater degree than blocking of JAK signaling directly. Furthermore, we demonstrated for the first time that IECs generated from genetically modified intestinal organoids, engineered to be deficient in the interferon response, were more permissive to HuNoV infection. Taking the results together, our work revealed that IFN-induced transcriptional responses restrict HuNoV replication in IECs and demonstrated that inhibition of these responses mediated by modifications of the culture conditions can greatly enhance the robustness of the norovirus culture system.IMPORTANCE Noroviruses are a major cause of gastroenteritis worldwide, and yet the challenges associated with their growth in culture have greatly hampered the development of therapeutic approaches and have limited our understanding of the cellular pathways that control infection. Here, we show that human intestinal epithelial cells, which represent the first point of entry of human noroviruses into the host, limit virus replication by induction of innate responses. Furthermore, we show that modulating the ability of intestinal epithelial cells to induce transcriptional responses to HuNoV infection can significantly enhance human norovirus replication in culture. Collectively, our findings provide new insights into the biological pathways that control norovirus infection but also identify mechanisms that enhance the robustness of norovirus culture.

Siglecs at the Host-Pathogen Interface

Siglecs are sialic acid (Sia) recognizing immunoglobulin-like receptors expressed on the surface of all the major leukocyte lineages in mammals. Siglecs recognize ubiquitous Sia epitopes on various glycoconjugates in the cell glycocalyx and transduce signals to regulate immunological and inflammatory activities of these cells. The subset known as CD33-related Siglecs is principally inhibitory receptors that suppress leukocyte activation, and recent research has shown that a number of bacterial pathogens use Sia mimicry to engage these Siglecs as an immune evasion strategy. Conversely, Siglec-1 is a macrophage phagocytic receptor that engages GBS and other sialylated bacteria to promote effective phagocytosis and antigen presentation for the adaptive immune response, whereas certain viruses and parasites use Siglec-1 to gain entry to immune cells as a proximal step in the infectious process. Siglecs are positioned in crosstalk with other host innate immune sensing pathways to modulate the immune response to infection in complex ways. This chapter summarizes the current understanding of Siglecs at the host-pathogen interface, a field of study expanding in breadth and medical importance, and which provides potential targets for immune-based anti-infective strategies.

Porcine reproductive and respiratory syndrome virus up-regulates sialoadhesin via IFN-STAT signaling to facilitate its infection

Porcine reproductive and respiratory syndrome (PRRS) has caused huge economic losses to global swine industry. Porcine sialoadhesin (poSn) was previously reported to be a putative receptor for the causative agent, PRRS virus (PRRSV). In the current study, we first observed that PRRSV infection up-regulated expression of poSn in a dose- and time-dependent manner. Subsequently, we found that PRRSV-triggered transcription of type I interferons (IFNs) was involved in poSn up-regulation through the IFN-signal transducer and activator of transcription (STAT) signaling cascade. Interestingly, poSn up-regulation was shown to promote PRRSV infection during post-entry process. Taken together, this work deepens our understanding of PRRSV pathogenesis and provides a novel idea on its establishment of persistent infection, which will be interesting to unravel the detailed mechanisms in the future.

Activation of sialoadhesin down-regulates the levels of innate antiviral cytokines in porcine alveolar macrophages in vitro

Porcine sialoadhesin (pSn) is a crucial porcine reproductive and respiratory syndrome virus (PRRSV) receptor mediating the attachment and internalization of virus into its major target cells, porcine alveolar macrophages (PAMs). However, the role of pSn in innate antiviral immune response has not yet been investigated. In this study, our results showed that PRRSV down-regulated significantly the mRNA levels of IFN-α, IFN-β, IFN-γ, IFN-λ1, IFN-λ3 and IFN-λ4 and up-regulated significantly the mRNA levels of IL-10 and pSn in infected PAMs in vitro, suggesting that PRRSV infection inhibited the transcription of innate antiviral cytokines in host cells. Our results also showed that selective activation of pSn down-regulated significantly the mRNA levels of IFN-α, IFN-β, IFN-γ, IFN-λ1, IFN-λ3, IFN-λ4 and TNF-α and up-regulated significantly the mRNA level of IL-10 in PAMs in vitro, suggesting that pSn signaling inhibited the transcription of innate antiviral cytokines. Further results showed that pSn1, pSn2, pSn3, pSn4 and pSn5 domains of pSn were responsible for the inhibition of levels of innate antiviral cytokines. In conclusion, our results suggested that pSn suppressed innate antiviral immune response by down-regulating the levels of innate antiviral cytokines in PAMs. It was possible that PRRSV-pSn interaction may suppress innate antiviral immune response to PRRSV infection by repressing the production of innate antiviral cytokines.

Critical role of OX40/OX40L in ILC2-mediated activation of CD4+T cells during respiratory syncytial virus infection in mice

CD4⁺T cells are crucial cellular source of type 2 cytokines and responsible for RSV-induced asthma-like symptoms and asthma exacerbations. However, the mechanism for regulating the activation of CD4⁺T cells during RSV infection is not clear completely. We show in this study that infection with RSV may induce an expansion and activation of CD4⁺T cells in the lungs of BALB/c mice. RSV-induced CD4⁺T cell expansion and activation seems to depend upon the pulmonary group 2 innate lymphoid cells (ILC2s), since adoptive transfer of lung ILC2s can enhance not only the numbers of CD4⁺T cells but also the cytokine production by CD4⁺T cells. Interestingly, blockade of the contact between ILC2s and CD4⁺T cells, may significantly diminish the CD4⁺T cell expansion and cytokine production, suggesting that membrane molecules may be involved in ILC2-regulated CD4⁺T cell activation. In fact, infection with RSV resulted in an increase in the numbers of OX40⁺CD4⁺T cells as well as OX40L⁺ILC2s in the lungs of mice. Moreover, the mRNA expressions of OX40 and OX40L as well as the levels of OX40 and OX40L proteins in the lung CD4⁺T cells and ILC2s were elevated respectively. When co-culture of CD4⁺T cells with ILC2s in the presence of anti-OX40L antibody, the cytokine productions by CD4⁺T cells were reduced markedly, suggesting that lung ILC2s may regulate RSV-induced CD4⁺T cell expansion and activation perhaps via OX40/OX40L interaction.