CCR5 is a required signaling receptor for macrophage expression of inflammatory genes in response to viral double-stranded RNA

Special Issue "Molecular and Genetic Aspects of SARS-CoV-2 Infection and COVID-19 Disease"

We are pleased to present the first and second editions of this Special Issue, titled "Molecular and Genetic Aspects of SARS-CoV-2 Infection and COVID-19 Disease", of the International Journal of Molecular Sciences [...].

Mixed Metal Components in PM2.5 Contribute to Chemokine Receptor CCR5-Mediated Neuroinflammation and Neuropathological Changes in the Mouse Olfactory Bulb

Particulate matter, especially PM2.5, can invade the central nervous system (CNS) via the olfactory pathway to induce neurotoxicity. The olfactory bulb (OB) is the key component integrating immunoprotection and olfaction processing and is necessarily involved in the relevant CNS health outcomes. Here we show that a microglial chemokine receptor, CCR5, is the target of environmentally relevant PM2.5 in the OB to trigger neuroinflammation and then neuropathological injuries. Mechanistically, PM2.5-induced CCR5 upregulation results in the pro-inflammatory paradigm of microglial activation, which subsequently activates TLR4-NF-κB neuroinflammation signaling and induces neuropathological changes that are closely related to neurodegenerative disorders (e.g., Aβ deposition and disruption of the blood-brain barrier). We specifically highlight that manganese and lead in PM2.5 are the main contributors to CCR5-mediated microglial activation and neuroinflammation in synergy with aluminum. Our results uncover a possible pathway of PM2.5-induced neuroinflammation and identify the principal neurotoxic components, which can provide new insight into efficiently diminishing the adverse health effects of PM2.5.

Targeting tumor-associated macrophages for cancer immunotherapy

Tumor-associated macrophages (TAMs) are one of the most abundant immune components in the tumor microenvironment and play a plethora of roles in regulating tumorigenesis. Therefore, the therapeutic targeting of TAMs has emerged as a new paradigm for immunotherapy of cancer. Herein, the review summarizes the origin, polarization, and function of TAMs in the progression of malignant diseases. The understanding of such knowledge leads to several distinct therapeutic strategies to manipulate TAMs to battle cancer, which include those to reduce TAM abundance, such as depleting TAMs or inhibiting their recruitment and differentiation, and those to harness or boost the anti-tumor activities of TAMs such as blocking phagocytosis checkpoints, inducing antibody-dependent cellular phagocytosis, and reprogramming TAM polarization. In addition, modulation of TAMs may reshape the tumor microenvironment and therefore synergize with other cancer therapeutics. Therefore, the rational combination of TAM-targeting therapeutics with conventional therapies including radiotherapy, chemotherapy, and other immunotherapies is also reviewed. Overall, targeting TAMs presents itself as a promising strategy to add to the growing repertoire of treatment approaches in the fight against cancer, and it is hopeful that these approaches currently being pioneered will serve to vastly improve patient outcomes and quality of life.

Targeting CCR5 as a Component of an HIV-1 Therapeutic Strategy

Globally, human immunodeficiency virus type 1 (HIV-1) infection is a major health burden for which successful therapeutic options are still being investigated. Challenges facing current drugs that are part of the established life-long antiretroviral therapy (ART) include toxicity, development of drug resistant HIV-1 strains, the cost of treatment, and the inability to eradicate the provirus from infected cells. For these reasons, novel anti-HIV-1 therapeutics that can prevent or eliminate disease progression including the onset of the acquired immunodeficiency syndrome (AIDS) are needed. While development of HIV-1 vaccination has also been challenging, recent advancements demonstrate that infection of HIV-1-susceptible cells can be prevented in individuals living with HIV-1, by targeting C-C chemokine receptor type 5 (CCR5). CCR5 serves many functions in the human immune response and is a co-receptor utilized by HIV-1 for entry into immune cells. Therapeutics targeting CCR5 generally involve gene editing techniques including CRISPR, CCR5 blockade using antibodies or antagonists, or combinations of both. Here we review the efficacy of these approaches and discuss the potential of their use in the clinic as novel ART-independent therapies for HIV-1 infection.

HIF-1α Regulation of Cytokine Production following TLR3 Engagement in Murine Bone Marrow-Derived Macrophages Is Dependent on Viral Nucleic Acid Length and Glucose Availability

Hypoxia-inducible factor-1α (HIF-1α) is an important regulator of glucose metabolism and inflammatory cytokine production in innate immune responses. Viruses modulate HIF-1α to support viral replication and the survival of infected cells, but it is unclear if this transcription factor also plays an important role in regulating antiviral immune responses. In this study, we found that short and long dsRNA differentially engage TLR3, inducing distinct levels of proinflammatory cytokine production (TNF-α and IL-6) in bone marrow-derived macrophages from C57BL/6 mice. These responses are associated with differential accumulation of HIF-1α, which augments NF-κB activation. Unlike TLR4 responses, increased HIF-1α following TLR3 engagement is not associated with significant alterations in glycolytic activity and was more pronounced in low glucose conditions. We also show that the mechanisms supporting HIF-1α stabilization may differ following stimulation with short versus long dsRNA and that pyruvate kinase M2 and mitochondrial reactive oxygen species play a central role in these processes. Collectively, this work suggests that HIF-1α may fine-tune proinflammatory cytokine production during early antiviral immune responses, particularly when there is limited glucose availability or under other conditions of stress. Our findings also suggest we may be able to regulate the magnitude of proinflammatory cytokine production during antiviral responses by targeting proteins or molecules that contribute to HIF-1α stabilization.

Molecular Pathogenesis and Immune Evasion of Vesicular Stomatitis New Jersey Virus Inferred from Genes Expression Changes in Infected Porcine Macrophages

The molecular mechanisms associated with the pathogenesis of vesicular stomatitis virus (VSV) in livestock remain poorly understood. Several studies have highlighted the relevant role of macrophages in controlling the systemic dissemination of VSV during infection in different animal models, including mice, cattle, and pigs. To gain more insight into the molecular mechanisms used by VSV to impair the immune response in macrophages, we used microarrays to determine the transcriptomic changes produced by VSV infection in primary cultures of porcine macrophages. The results indicated that VSV infection induced the massive expression of multiple anorexic, pyrogenic, proinflammatory, and immunosuppressive genes. Overall, the interferon (IFN) response appeared to be suppressed, leading to the absence of stimulation of interferon-stimulated genes (ISG). Interestingly, VSV infection promoted the expression of several genes known to downregulate the expression of IFNβ. This represents an alternate mechanism for VSV control of the IFN response, beyond the recognized mechanisms mediated by the matrix protein. Although there was no significant differential gene expression in macrophages infected with a highly virulent epidemic strain compared to a less virulent endemic strain, the endemic strain consistently induced higher expression of all upregulated cytokines and chemokines. Collectively, this study provides novel insights into VSV molecular pathogenesis and immune evasion that warrant further investigation.

Temporal omics analysis in Syrian hamsters unravel cellular effector responses to moderate COVID-19

In COVID-19, immune responses are key in determining disease severity. However, cellular mechanisms at the onset of inflammatory lung injury in SARS-CoV-2 infection, particularly involving endothelial cells, remain ill-defined. Using Syrian hamsters as a model for moderate COVID-19, we conduct a detailed longitudinal analysis of systemic and pulmonary cellular responses, and corroborate it with datasets from COVID-19 patients. Monocyte-derived macrophages in lungs exert the earliest and strongest transcriptional response to infection, including induction of pro-inflammatory genes, while epithelial cells show weak alterations. Without evidence for productive infection, endothelial cells react, depending on cell subtypes, by strong and early expression of anti-viral, pro-inflammatory, and T cell recruiting genes. Recruitment of cytotoxic T cells as well as emergence of IgM antibodies precede viral clearance at day 5 post infection. Investigating SARS-CoV-2 infected Syrian hamsters thus identifies cell type-specific effector functions, providing detailed insights into pathomechanisms of COVID-19 and informing therapeutic strategies.

Macrophage-Regulatory T Cell Interactions Promote Type 2 Immune Homeostasis Through Resistin-Like Molecule α

RELMα is a small, secreted protein expressed by type 2 cytokine-activated “M2” macrophages in helminth infection and allergy. At steady state and in response to type 2 cytokines, RELMα is highly expressed by peritoneal macrophages, however, its function in the serosal cavity is unclear. In this study, we generated RELMα TdTomato (Td) reporter/knockout (Rα^Td) mice and investigated RELMα function in IL-4 complex (IL-4c)-induced peritoneal inflammation. We first validated the RELMα^Td/Td transgenic mice and showed that IL-4c injection led to the significant expansion of large peritoneal macrophages that expressed Td but not RELMα protein, while RELMα^+/+ mice expressed RELMα and not Td. Functionally, RELMα^Td/Td mice had increased IL-4 induced peritoneal macrophage responses and splenomegaly compared to RELMα^+/+ mice. Gene expression analysis indicated that RELMα^Td/Td peritoneal macrophages were more proliferative and activated than RELMα^+/+ macrophages, with increased genes associated with T cell responses, growth factor and cytokine signaling, but decreased genes associated with differentiation and maintenance of myeloid cells. We tested the hypothesis that Rα^Td/Td macrophages drive aberrant T cell activation using peritoneal macrophage and T cell co-culture. There were no differences in CD4⁺ T cell effector responses when co-cultured with RELMα^+/+ or RELMα^Td/Td macrophages, however, RELMα^Td/Td macrophages were impaired in their ability to sustain proliferation of FoxP3⁺ regulatory T cells (Treg). Supportive of the in vitro results, immunofluorescent staining of the spleens revealed significantly decreased FoxP3⁺ cells in the RELMα^Td/Td spleens compared to RELMα^+/+ spleens. Taken together, these studies identify a new RELMα regulatory pathway whereby RELMα-expressing macrophages directly sustain Treg proliferation to limit type 2 inflammatory responses.

Regulatory Noncoding and Predicted Pathogenic Coding Variants of CCR5 Predispose to Severe COVID-19

Genome-wide association studies (GWAS) found locus 3p21.31 associated with severe COVID-19. CCR5 resides at the same locus and, given its known biological role in other infection diseases, we investigated if common noncoding and rare coding variants, affecting CCR5, can predispose to severe COVID-19. We combined single nucleotide polymorphisms (SNPs) that met the suggestive significance level (P ≤ 1 × 10-5) at the 3p21.31 locus in public GWAS datasets (6406 COVID-19 hospitalized patients and 902,088 controls) with gene expression data from 208 lung tissues, Hi-C, and Chip-seq data. Through whole exome sequencing (WES), we explored rare coding variants in 147 severe COVID-19 patients. We identified three SNPs (rs9845542, rs12639314, and rs35951367) associated with severe COVID-19 whose risk alleles correlated with low CCR5 expression in lung tissues. The rs35951367 resided in a CTFC binding site that interacts with CCR5 gene in lung tissues and was confirmed to be associated with severe COVID-19 in two independent datasets. We also identified a rare coding variant (rs34418657) associated with the risk of developing severe COVID-19. Our results suggest a biological role of CCR5 in the progression of COVID-19 as common and rare genetic variants can increase the risk of developing severe COVID-19 by affecting the functions of CCR5.

Brick plots: an intuitive platform for visualizing multiparametric immunophenotyped cell clusters

BACKGROUND

The advent of mass cytometry has dramatically increased the parameter limit for immunological analysis. New approaches to analysing high parameter cytometry data have been developed to ease analysis of these complex datasets. Many of these methods assign cells into population clusters based on protein expression similarity.

RESULTS

Here we introduce an additional method, termed Brick plots, to visualize these cluster phenotypes in a simplified and intuitive manner. The Brick plot method generates a two-dimensional barcode that displays the phenotype of each cluster in relation to the entire dataset. We show that Brick plots can be used to visualize complex mass cytometry data, both from fundamental research and clinical trials, as well as flow cytometry data.

CONCLUSION

Brick plots represent a new approach to visualize complex immunological data in an intuitive manner.

ACKR2 contributes to pulmonary dysfunction by shaping CCL5:CCR5-dependent recruitment of lymphocytes during influenza A infection in mice

Inflammation triggered by influenza A virus (IAV) infection is important for viral clearance, induction of adaptive responses, and return to lung homeostasis. However, an exaggerated immune response, characterized by the overproduction of chemokines, can lead to intense lung injury, contributing to mortality. Chemokine scavenger receptors, such as ACKR2, control the levels of CC chemokines influencing the immune responses. Among the chemokine targets of ACKR2, CCL5 is important to recruit and activate lymphocytes. We investigated the role of ACKR2 during IAV infection in mice. Pulmonary ACKR2 expression was increased acutely after IAV infection preceding the virus-induced lung dysfunction. ACKR2-knockout (ACKR2−/−) mice were protected from IAV, presenting decreased viral burden and lung dysfunction. Mechanistically, the absence of ACKR2 resulted in augmented airway CCL5 levels, secreted by mononuclear and plasma cells in the lung parenchyma. The higher chemokine gradient led to an augmented recruitment of T and B lymphocytes, formation of inducible bronchus-associated lymphoid tissue and production of IgA in the airways of ACKR2−/− mice post-IAV. CCL5 neutralization in ACKR2−/− mice prevented lymphocyte recruitment and increased bronchoalveolar lavage fluid protein levels and pulmonary dysfunction. Finally, CCR5−/− mice presented increased disease severity during IAV infection, displaying increased neutrophils, pulmonary injury and dysfunction, and accentuated lethality. Collectively, our data showed that ACKR2 dampens CCL5 levels and the consequent recruitment of CCR5+ T helper 1 (Th1), T regulatory cells (Tregs), and B lymphocytes during IAV infection, decreasing pathogen control and promoting lung dysfunction in wild type mice. Therefore, ACKR2 is detrimental and CCR5 is protective during IAV infection coordinating innate and adaptive immune responses in mice.

The location of sensing determines the pancreatic β-cell response to the viral mimetic dsRNA

Viral infection is an environmental trigger that has been suggested to initiate pancreatic β-cell damage, leading to the development of autoimmune diabetes. Viruses potently activate the immune system and can damage β cells by either directly infecting them or stimulating the production of secondary effector molecules (such as proinflammatory cytokines) during bystander activation. However, how and where β cells recognize viruses is unclear, and the antiviral responses that are initiated following virus recognition are incompletely understood. In this study, we show that the β-cell response to dsRNA, a viral replication intermediate known to activate antiviral responses, is determined by the cellular location of sensing (intracellular versus extracellular) and differs from the cellular response to cytokine treatment. Using biochemical and immunological methods, we show that β cells selectively respond to intracellular dsRNA by expressing type I interferons (IFNs) and inducing apoptosis, but that they do not respond to extracellular dsRNA. These responses differ from the activities of cytokines on β cells, which are mediated by inducible nitric oxide synthase expression and β-cell production of nitric oxide. These findings provide evidence that the antiviral activities of type I IFN production and apoptosis are elicited in β cells via the recognition of intracellular viral replication intermediates and that β cells lack the capacity to respond to extracellular viral intermediates known to activate innate immune responses.

Transcriptomic Analysis Reveals Priming of The Host Antiviral Interferon Signaling Pathway by Bronchobini® Resulting in Balanced Immune Response to Rhinovirus Infection in Mouse Lung Tissue Slices

Rhinovirus (RV) is the predominant virus causing respiratory tract infections. Bronchobini^® is a low dose multi component, multi target preparation used to treat inflammatory respiratory diseases such as the common cold, described to ease severity of symptoms such as cough and viscous mucus production. The aim of the study was to assess the efficacy of Bronchobini^® in RV infection and to elucidate its mode of action. Therefore, Bronchobini^®’s ingredients (BRO) were assessed in an ex vivo model of RV infection using mouse precision-cut lung slices, an organotypic tissue capable to reflect the host immune response to RV infection. Cytokine profiles were assessed using enzyme-linked immunosorbent assay (ELISA) and mesoscale discovery (MSD). Gene expression analysis was performed using Affymetrix microarrays and ingenuity pathway analysis. BRO treatment resulted in the significant suppression of RV-induced antiviral and pro-inflammatory cytokine release. Transcriptome analysis revealed a multifactorial mode of action of BRO, with a strong inhibition of the RV-induced pro-inflammatory and antiviral host response mediated by nuclear factor kappa B (NFkB) and interferon signaling pathways. Interestingly, this was due to priming of these pathways in the absence of virus. Overall, BRO exerted its beneficial anti-inflammatory effect by priming the antiviral host response resulting in a reduced inflammatory response to RV infection, thereby balancing an otherwise excessive inflammatory response.