Dendritic Cells and SARS-CoV-2 Infection: Still an Unclarified Connection

Microbiota and Immunity during Respiratory Infections: Lung and Gut Affair

Bacterial and viral respiratory tract infections are the most common infectious diseases, leading to worldwide morbidity and mortality. In the past 10 years, the importance of lung microbiota emerged in the context of pulmonary diseases, although the mechanisms by which it impacts the intestinal environment have not yet been fully identified. On the contrary, gut microbial dysbiosis is associated with disease etiology or/and development in the lung. In this review, we present an overview of the lung microbiome modifications occurring during respiratory infections, namely, reduced community diversity and increased microbial burden, and of the downstream consequences on host-pathogen interaction, inflammatory signals, and cytokines production, in turn affecting the disease progression and outcome. Particularly, we focus on the role of the gut-lung bidirectional communication in shaping inflammation and immunity in this context, resuming both animal and human studies. Moreover, we discuss the challenges and possibilities related to novel microbial-based (probiotics and dietary supplementation) and microbial-targeted therapies (antibacterial monoclonal antibodies and bacteriophages), aimed to remodel the composition of resident microbial communities and restore health. Finally, we propose an outlook of some relevant questions in the field to be answered with future research, which may have translational relevance for the prevention and control of respiratory infections.

The unique ORF8 protein from SARS-CoV-2 binds to human dendritic cells and induces a hyper-inflammatory cytokine storm

The novel coronavirus pandemic, first reported in December 2019, was caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infection leads to a strong immune response and activation of antigen-presenting cells, which can elicit acute respiratory distress syndrome (ARDS) characterized by the rapid onset of widespread inflammation, the so-called cytokine storm. In response to viral infections, monocytes are recruited into the lung and subsequently differentiate into dendritic cells (DCs). DCs are critical players in the development of acute lung inflammation that causes ARDS. Here, we focus on the interaction of a specific SARS-CoV-2 open reading frame protein, ORF8, with DCs. We show that ORF8 binds to DCs, causes pre-maturation of differentiating DCs, and induces the secretion of multiple proinflammatory cytokines by these cells. In addition, we identified DC-SIGN as a possible interaction partner of ORF8 on DCs. Blockade of ORF8 leads to reduced production of IL-1β, IL-6, IL-12p70, TNF-α, MCP-1 (also named CCL2), and IL-10 by DCs. Therefore, a neutralizing antibody blocking the ORF8-mediated cytokine and chemokine response could be an improved therapeutic strategy against SARS-CoV-2.

COVID-19 Vaccine in Renal Transplant Recipients: A Bibliometric-Based Analysis of Trends

BACKGROUND

The global community has been affected by COVID-19, which emerged in December 2019. Since then, many studies have been conducted on kidney transplant recipients (KTRs) and COVID-19. This study aimed to perform a bibliometric and visual analysis of the published relationship between KTRs and COVID-19.

OBJECTIVE

To discuss the current status, hot spots, and development trend of research on KTRs vaccination with the COVID-19 vaccine and to provide a reference for researchers in related fields.

METHODS

Visual analysis of countries/regions, institutions, authors, references cited, and keywords for 2020 to 2023 via Microsoft Office Excel 2019 and CiteSpace (6.1.R6) based on the Web of Science core database.

RESULTS

A total of 366 publications were included after screening, with a rapid increase in the global literature studying the COVID-19 vaccine of KTRs. The US has the highest number of publications, indicating that it is the leading country in this field of research. Charite University of Medicine Berlin and Schrezenmeier E are the most published institutions and authors, respectively. "Antibody Response After a Third Dose of the messenger RNA-1273 SARS-CoV-2 Vaccine in Kidney Transplant Recipients With Minimal Serologic Response to 2 Doses" is the most central co-cited reference; The keywords "kidney transplant recipient," "covid 19 vaccine," and "mortality" have become hot topics of research. The keywords "humoral response" and "bnt162b2" are the latest research frontiers for detecting bursts.

CONCLUSIONS

This paper analyzed the current status and trends of vaccination studies in KTRs through bibliometric analysis. Several studies support the vaccination of KTRs with the COVID-19 vaccine. However, the evidence for improving vaccine efficacy by adjustment of immunosuppression is still limited, and future studies on vaccination will remain a hot topic in this field.

The role of DC-SIGN as a trans-receptor in infection by MERS-CoV

DC-SIGN is a C-type lectin expressed in myeloid cells such as immature dendritic cells and macrophages. Through glycan recognition in viral envelope glycoproteins, DC-SIGN has been shown to act as a receptor for a number of viral agents such as HIV, Ebola virus, SARS-CoV, and SARS-CoV-2. Using a system of Vesicular Stomatitis Virus pseudotyped with MERS-CoV spike protein, here, we show that DC-SIGN is partially responsible for MERS-CoV infection of dendritic cells and that DC-SIGN efficiently mediates trans-infection of MERS-CoV from dendritic cells to susceptible cells, indicating a potential role of DC-SIGN in MERS-CoV dissemination and pathogenesis.

CuMV VLPs Containing the RBM from SARS-CoV-2 Spike Protein Drive Dendritic Cell Activation and Th1 Polarization

Dendritic cells (DCs) are the most specialized and proficient antigen-presenting cells. They bridge innate and adaptive immunity and display a powerful capacity to prime antigen-specific T cells. The interaction of DCs with the receptor-binding domain of the spike (S) protein from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pivotal step to induce effective immunity against the S protein-based vaccination protocols, as well as the SARS-CoV-2 virus. Herein, we describe the cellular and molecular events triggered by virus-like particles (VLPs) containing the receptor-binding motif from the SARS-CoV-2 spike protein in human monocyte-derived dendritic cells, or, as controls, in the presence of the Toll-like receptors (TLR)3 and TLR7/8 agonists, comprehending the events of dendritic cell maturation and their crosstalk with T cells. The results demonstrated that VLPs boosted the expression of major histocompatibility complex molecules and co-stimulatory receptors of DCs, indicating their maturation. Furthermore, DCs’ interaction with VLPs promoted the activation of the NF-kB pathway, a very important intracellular signalling pathway responsible for triggering the expression and secretion of proinflammatory cytokines. Additionally, co-culture of DCs with T cells triggered CD4+ (mainly CD4+Tbet+) and CD8+ T cell proliferation. Our results suggested that VLPs increase cellular immunity, involving DC maturation and T cell polarization towards a type 1 T cells profile. By providing deeper insight into the mechanisms of activation and regulation of the immune system by DCs, these findings will enable the design of effective vaccines against SARS-CoV-2.

Potent NKT cell ligands overcome SARS-CoV-2 immune evasion to mitigate viral pathogenesis in mouse models

One of the major pathogenesis mechanisms of SARS-CoV-2 is its potent suppression of innate immunity, including blocking the production of type I interferons. However, it is unknown whether and how the virus interacts with different innate-like T cells, including NKT, MAIT and γδ T cells. Here we reported that upon SARS-CoV-2 infection, invariant NKT (iNKT) cells rapidly trafficked to infected lung tissues from the periphery. We discovered that the envelope (E) protein of SARS-CoV-2 efficiently down-regulated the cell surface expression of the antigen-presenting molecule, CD1d, to suppress the function of iNKT cells. E protein is a small membrane protein and a viroporin that plays important roles in virion packaging and envelopment during viral morphogenesis. We showed that the transmembrane domain of E protein was responsible for suppressing CD1d expression by specifically reducing the level of mature, post-ER forms of CD1d, suggesting that it suppressed the trafficking of CD1d proteins and led to their degradation. Point mutations demonstrated that the putative ion channel function was required for suppression of CD1d expression and inhibition of the ion channel function using small chemicals rescued the CD1d expression. Importantly, we discovered that among seven human coronaviruses, only E proteins from highly pathogenic coronaviruses including SARS-CoV-2, SARS-CoV and MERS suppressed CD1d expression, whereas the E proteins of human common cold coronaviruses, HCoV-OC43, HCoV-229E, HCoV-NL63 and HCoV-HKU1, did not. These results suggested that E protein-mediated evasion of NKT cell function was likely an important pathogenesis factor, enhancing the virulence of these highly pathogenic coronaviruses. Remarkably, activation of iNKT cells with their glycolipid ligands, both prophylactically and therapeutically, overcame the putative viral immune evasion, significantly mitigated viral pathogenesis and improved host survival in mice. Our results suggested a novel NKT cell-based anti-SARS-CoV-2 therapeutic approach.

Major alterations to monocyte and dendritic cell subsets lasting more than 6 months after hospitalization for COVID-19

Introduction

After more than two years the Coronavirus disease-19 (COVID-19) pandemic continues to burden healthcare systems and economies worldwide, and it is evident that the effects on the immune system can persist for months post-infection. The activity of myeloid cells such as monocytes and dendritic cells (DC) is essential for correct mobilization of the innate and adaptive responses to a pathogen. Impaired levels and responses of monocytes and DC to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is likely to be a driving force behind the immune dysregulation that characterizes severe COVID-19.

Methods

Here, we followed a cohort of COVID-19 patients hospitalized during the early waves of the pandemic for 6-7 months. The levels and phenotypes of circulating monocyte and DC subsets were assessed to determine both the early and long-term effects of the SARS-CoV-2 infection.

Results

We found increased monocyte levels that persisted for 6-7 months, mostly attributed to elevated levels of classical monocytes. Myeloid derived suppressor cells were also elevated over this period. While most DC subsets recovered from an initial decrease, we found elevated levels of cDC2/cDC3 at the 6-7 month timepoint. Analysis of functional markers on monocytes and DC revealed sustained reduction in program death ligand 1 (PD-L1) expression but increased CD86 expression across almost all cell types examined. Finally, C-reactive protein (CRP) correlated positively to the levels of intermediate monocytes and negatively to the recovery of DC subsets.

Conclusion

By exploring the myeloid compartments, we show here that alterations in the immune landscape remain more than 6 months after severe COVID-19, which could be indicative of ongoing healing and/or persistence of viral antigens.

Cellular immune states in SARS-CoV-2-induced disease

The general immune state plays important roles against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Cells of the immune system are encountering rapid changes during the acute phase of SARS-CoV-2-induced disease. Reduced fraction of functional CD8⁺ T cells, disrupted cross-talking between CD8⁺ T cells with dendritic cells (DCs), and impaired immunological T-cell memory, along with the higher presence of hyperactive neutrophils, high expansion of myeloid-derived suppressor cells (MDSCs) and non-classical monocytes, and attenuated cytotoxic capacity of natural killer (NK) cells, are all indicative of low efficient immunity against viral surge within the body. Immune state and responses from pro- or anti-inflammatory cells of the immune system to SARS-CoV-2 are discussed in this review. We also suggest some strategies to enhance the power of immune system against SARS-CoV-2-induced disease.

Hypocalcemia: a key biomarker in hospitalized COVID-19 patients

Background

At the end of 2019 a new respiratory syndrome emerged in China named Coronavirus disease 2019 (COVID-19) due to SARS-CoV-2 infection. Considering the severity of the disease in adult subjects with one or more chronic pathologies, it was mandatory to find simple and effective biomarkers for negative prognosis of the disease easily available at the admission to the hospital.

Methods

To identify possible parameters showing association with the outcome in COVID-19 patients with pre-existing chronic diseases, blood biochemical profiles of 511 patients, enrolled from March to June 2020, were retrospectively evaluated. The pathological conditions taken into consideration were diabetes, arterial hypertension, chronic kidney disease, cardiovascular diseases, chronic obstructive pulmonary disease, obesity, and cancer. All the data were collected upon admission to the emergency room (ER) during the indicated period.

Results

We observed that serum and ionized calcium were prevalently altered in our cohort. We determined that hypocalcemia was a major parameter associated with mechanical ventilation and poor prognosis, correlating also with the presence of comorbidities such as cardiovascular diseases, chronic kidney disease, and cancer. In addition, we found a positive correlation between hypocalcemia and clinical complications during hospitalizations.

Conclusions

Our results strengthen the relevance of serum calcium concentration as a useful prognostic biomarker in hospitalized COVID-19 patients.

Immunouniverse of SARS-CoV-2

SARS-CoV-2 virus has become a global health problem that has caused millions of deaths worldwide. The infection can present with multiple clinical features ranging from asymptomatic or mildly symptomatic patients to patients with severe or critical illness that can even lead to death. Although the immune system plays an important role in pathogen control, SARS-CoV-2 can drive dysregulation of this response and trigger severe immunopathology. Exploring the mechanisms of the immune response involved in host defense against SARS-CoV-2 allows us to understand its immunopathogenesis and possibly detect features that can be used as potential therapies to eliminate the virus. The main objective of this review on SARS-CoV-2 is to highlight the interaction between the virus and the immune response. We explore the function and action of the immune system, the expression of molecules at the site of infection that cause hyperinflammation and hypercoagulation disorders, the factors leading to the development of pneumonia and subsequent severe acute respiratory distress syndrome which is the leading cause of death in patients with COVID-19.

The role of antigen-presenting cells in the pathogenesis of COVID-19

Coronavirus Disease 2019 (COVID-19) is one of the three lethal coronavirus outbreaks in the recent two decades and a serious threat to global health all over the world. The principal feature of the COVID-19 infection is the so-called "cytokine storm" exaggerated molecular response to virus distribution, which plays massive tissue and organ injury roles. Immunological treatments, including monoclonal antibodies and vaccines, have been suggested as the main approaches in treating and preventing this disease. Therefore, a proper investigation of the roles of antigen-presenting cells (APCs) in the aforementioned immunological responses appears essential. The present review will provide detailed information about APCs' role in the infection and pathogenesis of SARS-CoV-2 and the effect of monoclonal antibodies in diagnosis and treatment.

The Role of Cytokines and Chemokines in Severe Acute Respiratory Syndrome Coronavirus 2 Infections

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in countless infections and caused millions of deaths since its emergence in 2019. Coronavirus disease 2019 (COVID-19)-associated mortality is caused by uncontrolled inflammation, aberrant immune response, cytokine storm, and an imbalanced hyperactive immune system. The cytokine storm further results in multiple organ failure and lung immunopathology. Therefore, any potential treatments should focus on the direct elimination of viral particles, prevention strategies, and mitigation of the imbalanced (hyperactive) immune system. This review focuses on cytokine secretions of innate and adaptive immune responses against COVID-19, including interleukins, interferons, tumor necrosis factor-alpha, and other chemokines. In addition to the review focus, we discuss potential immunotherapeutic approaches based on relevant pathophysiological features, the systemic immune response against SARS-CoV-2, and data from recent clinical trials and experiments on the COVID-19-associated cytokine storm. Prompt use of these cytokines as diagnostic markers and aggressive prevention and management of the cytokine storm can help determine COVID-19-associated morbidity and mortality. The prophylaxis and rapid management of the cytokine storm appear to significantly improve disease outcomes. For these reasons, this study aims to provide advanced information to facilitate innovative strategies to survive in the COVID-19 pandemic.

Identification of Distinct Immune Cell Subsets Associated With Asymptomatic Infection, Disease Severity, and Viral Persistence in COVID-19 Patients

The cell-mediated protective and pathogenic immune responses to SARS-CoV-2 infection remain largely elusive. Here we identified 76 distinct cell subsets in the PBMC samples that were associated with various clinical presentations of COVID-19 using scRNA-seq technology coupled with a deep and comprehensive analysis of unique cell surface markers and differentially expressed genes. We revealed that (TRAV1-2⁺CD8⁺)MAIT cells and (NCAM1^hiCD160⁺)NK cells significantly enriched in the asymptomatic subjects whereas (LAG3⁺CD160⁺CD8⁺)NKT cells increased in the symptomatic patients. We also observed that (CD68^-CSF1R^-IL1B^hiCD14⁺)classical monocytes were positively correlated with the disease severity. Moreover, (CD33^-HLA-DMA^-CD14⁺)classical monocytes and (CLEC10A^-S100A9^lo)pDC were associated with the viral persistence. The GO and KEGG analyses identified enriched pathways related to immune responses, inflammation, and apoptosis. These findings may enhance our understanding of the immunopathogenesis of COVID-19 and help develop novel strategies against SARS-CoV-2 infection.

Depletion and Dysfunction of Dendritic Cells: Understanding SARS-CoV-2 Infection

Uncontrolled severe acute respiratory syndrome-coronavirus (SARS-CoV)-2 infection is closely related to disorders of the innate immune and delayed adaptive immune systems. Dendritic cells (DCs) “bridge” innate immunity and adaptive immunity. DCs have important roles in defending against SARS-CoV-2 infection. In this review, we summarize the latest research concerning the role of DCs in SARS-CoV-2 infection. We focus on the complex interplay between DCs and SARS-CoV-2: pyroptosis-induced activation; activation of the renin–angiotensin–aldosterone system; and activation of dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin. We also discuss the decline in DC number, the impaired antigen-presentation capability, and the reduced production of type-I interferon of DCs in severe SARS-CoV-2 infection. In addition, we discuss the potential mechanisms for pathological activation of DCs to understand the pattern of SARS-CoV-2 infection. Lastly, we provide a brief overview of novel vaccination and immunotherapy strategies based on DC targeting to overcome SARS-CoV-2 infection.

Inhalable SARS-CoV-2 Mimetic Particles Induce Pleiotropic Antigen Presentation

Coronavirus disease 2019 (Covid-19) has caused over 5.5 million deaths worldwide, and viral mutants continue to ravage communities with limited access to injectable vaccines or high rates of vaccine hesitancy. Inhalable vaccines have the potential to address these distribution and compliance issues as they are less likely to require cold storage, avoid the use of needles, and can elicit localized immune responses with only a single dose. Alveolar macrophages represent attractive targets for inhalable vaccines as they are abundant within the lung mucosa (up to 95% of all immune cells) and are important mediators of mucosal immunity, and evidence suggests that they may be key cellular players in early Covid-19 pathogenesis. Here, we report inhalable coronavirus mimetic particles (CoMiP) designed to rapidly bind to, and be internalized by, alveolar macrophages to deliver nucleic acid-encoded viral antigens. Inspired by the SARS-CoV-2 virion structure, CoMiP carriers package nucleic acid cargo within an endosomolytic peptide envelope that is wrapped in a macrophage-targeting glycosaminoglycan coating. Through this design, CoMiP mimic several important features of the SARS-CoV-2 virion, particularly surface topography and macromolecular chemistry. As a result, CoMiP effect pleiotropic transfection of macrophages and lung epithelial cells in vitro with multiple antigen-encoding plasmids. In vivo immunization yields increased mucosal IgA levels within the respiratory tract of CoMiP vaccinated mice.

Insights into the immune responses of SARS-CoV-2 in relation to COVID-19 vaccines

The three types of approved coronavirus disease 2019 (COVID-19) vaccines that have been emergency-use listed (EUL) by the World Health Organization are mRNA vaccines, adenovirus-vectored vaccines, and inactivated vaccines. Canonical vaccine developments usually take years or decades to be completed to commercialization; however, the EUL vaccines being used in the current situation comprise several COVID-19 vaccine candidates applied in studies and clinical settings across the world. The extraordinary circumstances of the COVID-19 pandemic have necessitated the emergency authorization of these EUL vaccines, which have been rapidly developed. Although the benefits of the EUL vaccines outweigh their adverse effects, there have been reports of rare but fatal cases directly associated with COVID-19 vaccinations. Thus, a reassessment of the immunological rationale underlying EUL vaccines in relation to COVID-19 caused by SARSCOV-2 virus infection is now required. In this review, we discuss the manifestations of COVID-19, immunologically projected effects of EUL vaccines, reported immune responses, informed issues related to COVID-19 vaccination, and the potential strategies for future vaccine use against antigenic variants.

SARS-CoV-2 infection activates dendritic cells via cytosolic receptors rather than extracellular TLRs

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) causes coronavirus disease 2019 (COVID‐19), an infectious disease characterized by strong induction of inflammatory cytokines, progressive lung inflammation, and potentially multiorgan dysfunction. It remains unclear how SARS‐CoV‐2 infection leads to immune activation. The Spike (S) protein of SARS‐CoV‐2 has been suggested to trigger TLR4 and thereby activate immunity. Here, we have investigated the role of TLR4 in SARS‐CoV‐2 infection and immunity. Neither exposure of isolated S protein, SARS‐CoV‐2 pseudovirus nor primary SARS‐CoV‐2 isolate induced TLR4 activation in a TLR4‐expressing cell line. Human monocyte‐derived DCs express TLR4 but not angiotensin converting enzyme 2 (ACE2), and DCs were not infected by SARS‐CoV‐2. Notably, neither S protein nor SARS‐CoV‐2 induced DC maturation or cytokines, indicating that both S protein and SARS‐CoV‐2 virus particles do not trigger extracellular TLRs including TLR4. Ectopic expression of ACE2 in DCs led to efficient infection by SARS‐CoV‐2 and, strikingly, efficient type I IFN and cytokine responses. These data strongly suggest that not extracellular TLRs but intracellular viral sensors are key players in sensing SARS‐CoV‐2. These data imply that SARS‐CoV‐2 escapes direct sensing by TLRs, which might underlie the lack of efficient immunity to SARS‐CoV‐2 early during infection.

Postmortem high-dimensional immune profiling of severe COVID-19 patients reveals distinct patterns of immunosuppression and immunoactivation

A complete diagnostic autopsy is the gold-standard to gain insight into Coronavirus disease 2019 (COVID-19) pathogenesis. To delineate the in situ immune responses to SARS-CoV-2 viral infection, here we perform comprehensive high-dimensional transcriptional and spatial immune profiling in 22 COVID-19 decedents from Wuhan, China. We find TIM-3-mediated and PD-1-mediated immunosuppression as a hallmark of severe COVID-19, particularly in men, with PD-1+ cells being proximal rather than distal to TIM-3+ cells. Concurrently, lymphocytes are distal, while activated myeloid cells are proximal, to SARS-CoV-2 viral antigens, consistent with prevalent SARS-CoV-2 infection of myeloid cells in multiple organs. Finally, viral load positively correlates with specific immunosuppression and dendritic cell markers. In summary, our data show that SARS-CoV-2 viral infection induces lymphocyte suppression yet myeloid activation in severe COVID-19, so these two cell types likely have distinct functions in severe COVID-19 disease progression, and should be targeted differently for therapy.

SARS-CoV-2 and HIV-1: So Different yet so Alike. Immune Response at the Cellular and Molecular Level

In the past half century, humanity has experienced two devastating pandemics; the HIV-1 pandemic and the recent pandemic caused by SARS-CoV-2. Both emerged as zoonotic pathogens. Interestingly, SARS-CoV-2 has rapidly migrated all over the world in less than two years, much as HIV-1 did almost 40 years ago. Despite these two RNA viruses being different in their mode of transmission as well as the symptoms they generate, recent evidence suggests that they cause similar immune responses. In this mini review, we compare the molecular basis for CD4⁺ T cell lymphopenia and other effects on the immune system induced by SARS-CoV-2 and HIV-1 infections. We considered features of the host immune response that are shared with HIV-1 and could account for the lymphopenia and other immune effects observed in COVID-19. The information provided herein, may cast the virus-induced lymphopenia and cytokine storm associated with the acute SARS-CoV-2 infection and pathogenesis in a different light for further research on host immune responses. It can also provide opportunities for the identification of novel therapeutic targets for COVID-19. Furthermore, we provide some basic information to enable a comparative framework for considering the overlapping sets of immune responses caused by HIV-1 and SARS-CoV-2.

Langerhans cells and cDC1s play redundant roles in mRNA-LNP induced protective anti-influenza and anti-SARS-CoV-2 immune responses

Nucleoside modified mRNA combined with Acuitas Therapeutics' lipid nanoparticles (LNPs) has been shown to support robust humoral immune responses in many preclinical animal vaccine studies and later in humans with the SARS-CoV-2 vaccination. We recently showed that this platform is highly inflammatory due to the LNPs' ionizable lipid component. The inflammatory property is key to support the development of potent humoral immune responses. However, the mechanism by which this platform drives T follicular helper (Tfh) cells and humoral immune responses remains unknown. Here we show that lack of Langerhans cells or cDC1s neither significantly affected the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cells and humoral immune responses, nor susceptibility towards the lethal challenge of influenza and SARS-CoV-2. However, the combined deletion of these two DC subsets led to a significant decrease in the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cell and humoral immune responses. Despite these observed defects, these mice remained protected from lethal influenza and SARS-CoV-2 challenges. We further found that IL-6, unlike neutrophils, was required to generate normal Tfh cells and antibody responses, but not for protection from influenza challenge. In summary, here we bring evidence that the mRNA-LNP platform can support the induction of protective immune responses in the absence of certain innate immune cells and cytokines.

A bird's eye view on the role of dendritic cells in SARS-CoV-2 infection: Perspectives for immune-based vaccines

Coronavirus disease-19 (COVID-19) is a complex disorder caused by the pandemic diffusion of a novel coronavirus named SARS-CoV-2. Clinical manifestations vary from silent infection to severe pneumonia, disseminated thrombosis, multi-organ failure, and death. COVID-19 pathogenesis is still not fully elucidated, while increasing evidence suggests that disease phenotypes are strongly related to the virus-induced immune system's dysregulation. Indeed, when the virus-host cross talk is out of control, the occurrence of an aberrant systemic inflammatory reaction, named "cytokine storm," leads to a detrimental impairment of the adaptive immune response. Dendritic cells (DCs) are the most potent antigen-presenting cells able to support innate immune and promote adaptive responses. Besides, DCs play a key role in the anti-viral defense. The aim of this review is to focus on DC involvement in SARS-CoV-2 infection to better understand pathogenesis and clinical behavior of COVID-19 and explore potential implications for immune-based therapy strategies.

Perspectives and potential approaches for targeting neuropilin 1 in SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel type b coronavirus responsible for the COVID-19 pandemic. With over 224 million confirmed infections with this virus and more than 4.6 million people dead because of it, it is critically important to define the immunological processes occurring in the human response to this virus and pathogenetic mechanisms of its deadly manifestation. This perspective focuses on the contribution of the recently discovered interaction of SARS-CoV-2 Spike protein with neuropilin 1 (NRP1) receptor, NRP1 as a virus entry receptor for SARS-CoV-2, its role in different physiologic and pathologic conditions, and the potential to target the Spike-NRP1 interaction to combat virus infectivity and severe disease manifestations.

The Immunopathobiology of SARS-CoV-2 Infection

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can lead to coronavirus disease 2019 (COVID-19). Virus-specific immunity controls infection, transmission and disease severity. With respect to disease severity, a spectrum of clinical outcomes occur associated with age, genetics, comorbidities and immune responses in an infected person. Dysfunctions in innate and adaptive immunity commonly follow viral infection. These are heralded by altered innate mononuclear phagocyte differentiation, activation, intracellular killing and adaptive memory, effector, and regulatory T cell responses. All of such affect viral clearance and the progression of end-organ disease. Failures to produce effective controlled antiviral immunity leads to life-threatening end-organ disease that is typified by the acute respiratory distress syndrome. The most effective means to contain SARS-CoV-2 infection is by vaccination. While an arsenal of immunomodulators were developed for control of viral infection and subsequent COVID-19 disease, further research is required to enable therapeutic implementation.

SARS-CoV-2 Spike Protein and Its Receptor Binding Domain Promote a Proinflammatory Activation Profile on Human Dendritic Cells

Dendritic cells (DCs) are the most potent antigen-presenting cells, and their function is essential to configure adaptative immunity and avoid excessive inflammation. DCs are predicted to play a crucial role in the clinical evolution of the infection by the severe acute respiratory syndrome (SARS) coronavirus (CoV)-2. DCs interaction with the SARS-CoV-2 Spike protein, which mediates cell receptor binding and subsequent fusion of the viral particle with host cell, is a key step to induce effective immunity against this virus and in the S protein-based vaccination protocols. Here we evaluated human DCs in response to SARS-CoV-2 S protein, or to a fragment encompassing the receptor binding domain (RBD) challenge. Both proteins increased the expression of maturation markers, including MHC molecules and costimulatory receptors. DCs interaction with the SARS-CoV-2 S protein promotes activation of key signaling molecules involved in inflammation, including MAPK, AKT, STAT1, and NFκB, which correlates with the expression and secretion of distinctive proinflammatory cytokines. Differences in the expression of ACE2 along the differentiation of human monocytes to mature DCs and inter-donor were found. Our results show that SARS-CoV-2 S protein promotes inflammatory response and provides molecular links between individual variations and the degree of response against this virus.

Innate Immunity Evasion Strategies of Highly Pathogenic Coronaviruses: SARS-CoV, MERS-CoV, and SARS-CoV-2

In the past two decades, coronavirus (CoV) has emerged frequently in the population. Three CoVs (SARS-CoV, MERS-CoV, SARS-CoV-2) have been identified as highly pathogenic human coronaviruses (HP-hCoVs). Particularly, the ongoing COVID-19 pandemic caused by SARS-CoV-2 warns that HP-hCoVs present a high risk to human health. Like other viruses, HP-hCoVs interact with their host cells in sophisticated manners for infection and pathogenesis. Here, we reviewed the current knowledge about the interference of HP-hCoVs in multiple cellular processes and their impacts on viral infection. HP-hCoVs employed various strategies to suppress and evade from immune response, including shielding viral RNA from recognition by pattern recognition receptors (PRRs), impairing IFN-I production, blocking the downstream pathways of IFN-I, and other evasion strategies. This summary provides a comprehensive view of the interplay between HP-hCoVs and the host cells, which is helpful to understand the mechanism of viral pathogenesis and develop antiviral therapies.

A Review of Human Coronaviruses' Receptors: The Host-Cell Targets for the Crown Bearing Viruses

A novel human coronavirus prompted considerable worry at the end of the year 2019. Now, it represents a significant global health and economic burden. The newly emerged coronavirus disease caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the primary reason for the COVID-19 global pandemic. According to recent global figures, COVID-19 has caused approximately 243.3 million illnesses and 4.9 million deaths. Several human cell receptors are involved in the virus identification of the host cells and entering them. Hence, understanding how the virus binds to host-cell receptors is crucial for developing antiviral treatments and vaccines. The current work aimed to determine the multiple host-cell receptors that bind with SARS-CoV-2 and other human coronaviruses for the purpose of cell entry. Extensive research is needed using neutralizing antibodies, natural chemicals, and therapeutic peptides to target those host-cell receptors in extremely susceptible individuals. More research is needed to map SARS-CoV-2 cell entry pathways in order to identify potential viral inhibitors.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

Comprehensive immune cell profiling depicts an early immune response associated with severe coronavirus disease 2019 in cancer patients

Recent studies have highlighted multiple immune perturbations related to severe acute respiratory syndrome coronavirus 2 infection-associated respiratory disease [coronavirus disease 2019 (COVID-19)]. Some of them were associated with immunopathogenesis of severe COVID-19. However, reports on immunological indicators of severe COVID-19 in the early phase of infection in patients with comorbidities such as cancer are scarce. We prospectively studied about 200 immune response parameters, including a comprehensive immune-cell profile, inflammatory cytokines and other parameters, in 95 patients with COVID-19 (37 cancer patients without active disease and intensive chemo/immunotherapy, 58 patients without cancer) and 21 healthy donors. Of 95 patients, 41 had severe disease, and the remaining 54 were categorized as having a nonsevere disease. We evaluated the association of immune response parameters with severe COVID-19. By principal component analysis, three immune signatures defining characteristic immune responses in COVID-19 patients were found. Immune cell perturbations, in particular, decreased levels of circulating dendritic cells (DCs) along with reduced levels of CD4 T-cell subsets such as regulatory T cells (T_regs ), type 1 T helper (Th1) and Th9; additionally, relative expansion of effector natural killer (NK) cells were significantly associated with severe COVID-19. Compared with patients without cancer, the levels of terminal effector CD4 T cells, T_regs , Th9, effector NK cells, B cells, intermediate-type monocytes and myeloid DCs were significantly lower in cancer patients with mild and severe COVID-19. We concluded that severely depleted circulating myeloid DCs and helper T subsets in the initial phase of infection were strongly associated with severe COVID-19 independent of age, type of comorbidity and other parameters. Thus, our study describes the early immune response associated with severe COVID-19 in cancer patients without intensive chemo/immunotherapy.

An overview on tumor treating fields (TTFields) technology as a new potential subsidiary biophysical treatment for COVID-19

COVID-19 pandemic situation has affected millions of people with tens of thousands of deaths worldwide. Despite all efforts for finding drugs or vaccines, the key role for the survival of patients is still related to the immune system. Therefore, improving the efficacy and the functionality of the immune system of COVID-19 patients is very crucial. The potential new, non-invasive, FDA-approved biophysical technology that could be considered in this regard is tumor treating fields (TTFields) based on an alternating electric field has great biological effects. TTFields have significant effects in improving the functionality of dendritic cell, and cytotoxic T-cells, and these cells have a major role in defense against viral infection. Hence, applying TTFields could help COVID-19 patients against infection. Additionally, TTFields can reduce viral genomic replication, by reducing the expressions of some of the vital members of DNA replication complex genes from the minichromosome maintenance family (MCMs). These genes not only are involved in DNA replication but it has also been proven that they have a crucial role in viral replication. Also, TTFields suppress the formation of the network of tunneling nanotubes (TNTs) which is knows as filamentous (F)-actin-rich tubular structures. TNTs have a critical role in promoting the spread of viruses through improving viral entry and acting as a protective agent for viral components from immune cells and even pharmaceuticals. Moreover, TTFields enhance autophagy which leads to apoptosis of virally infected cells. Thus, it can be speculated that using TTFields may prove to be a promising approach as a subsidiary treatment of COVID-19.

Crosstalk between estrogen, dendritic cells, and SARS-CoV-2 infection

The novel coronavirus disease 2019 (Covid‐19) first appeared in Wuhan and has so far killed more than four million people worldwide. Men are more affected than women by Covid‐19, but the cellular and molecular mechanisms behind these differences are largely unknown. One plausible explanation is that differences in sex hormones could partially account for this distinct prevalence in both sexes. Accordingly, several papers have reported a protective role of 17β‐estradiol during Covid‐19, which might help explain why women appear less likely to die from Covid‐19 than men. 17β‐estradiol is the predominant and most biologically active endogenous estrogen, which signals through estrogen receptor α, estrogen receptor β, and G protein‐coupled estrogen receptor 1. These receptors are expressed in mature cells from the innate and the adaptive immune system, particularly on dendritic cells (DCs), suggesting that estrogens could modulate their effector functions. DCs are the most specialized and proficient antigen‐presenting cells, acting at the interface of innate and adaptive immunity with a powerful capacity to prime antigen‐specific naive CD8+ T cells. DCs are richly abundant in the lung where they respond to viral infection. A relative increase of mature DCs in broncho‐alveolar lavage fluids from Covid‐19 patients has already been reported. Here we will describe how SARS‐CoV‐2 acts on DCs, the role of estrogen on DC immunobiology, summarise the impact of sex hormones on the immune response against Covid‐19, and explore clinical trials regarding Covid‐19

Respiratory Nasal Mucosa in Chronic Rhinosinusitis with Nasal Polyps versus COVID-19: Histopathology, Electron Microscopy Analysis and Assessing of Tissue Interleukin-33

(1) Background: Chronic rhinosinusitis with nasal polyps (CRSwNP) is one of the most studied rhinological disorders. Modifications of the respiratory nasal mucosa in COVID-19 patients are so far unknown. This paper presents a comparative morphological characterization of the respiratory nasal mucosa in CRSwNP versus COVID-19 and tissue interleukin (IL)-33 concentration. (2) Methods: We analyzed CRSwNP and COVID-19 samples through histopathology, scanning and transmission electron microscopy and performed proteomic determination of IL-33. (3) Results: Histopathologically, stromal edema (p < 0.0001) and basal membrane thickening (p = 0.0768) were found more frequently in CRSwNP than in COVID-19. Inflammatory infiltrate was mainly eosinophil-dominant in CRSwNP and lymphocyte-dominant in COVID-19 (p = 0.3666). A viral cytopathic effect was identified in COVID-19. Scanning electron microscopy detected biofilms only in CRSwNP, while most COVID-19 samples showed microbial aggregates (p = 0.0148) and immune cells (p = 0.1452). Transmission electron microscopy of CRSwNP samples identified biofilms, mucous cell hyperplasia (p = 0.0011), eosinophils, fibrocytes, mastocytes, and collagen fibers. Extracellular suggestive structures for SARS-CoV-2 and multiple Golgi apparatus in epithelial cells were detected in COVID-19 samples. The tissue IL-33 concentration in CRSwNP (210.0 pg/7 μg total protein) was higher than in COVID-19 (52.77 pg/7 μg total protein) (p < 0.0001), also suggesting a different inflammatory pattern. (4) Conclusions: The inflammatory pattern is different in each of these disorders. Results suggested the presence of nasal dysbiosis in both conditions, which could be a determining factor in CRSwNP and a secondary factor in COVID-19.

Viral and Bacterial Co-Infections in the Lungs: Dangerous Liaisons

Respiratory tract infections constitute a significant public health problem, with a therapeutic arsenal that remains relatively limited and that is threatened by the emergence of antiviral and/or antibiotic resistance. Viral–bacterial co-infections are very often associated with the severity of these respiratory infections and have been explored mainly in the context of bacterial superinfections following primary influenza infection. This review summarizes our current knowledge of the mechanisms underlying these co-infections between respiratory viruses (influenza viruses, RSV, and SARS-CoV-2) and bacteria, at both the physiological and immunological levels. This review also explores the importance of the microbiome and the pathological context in the evolution of these respiratory tract co-infections and presents the different in vitro and in vivo experimental models available. A better understanding of the complex functional interactions between viruses/bacteria and host cells will allow the development of new, specific, and more effective diagnostic and therapeutic approaches.

Langerhans cells and cDC1s play redundant roles in mRNA-LNP induced protective anti-influenza and anti-SARS-CoV-2 responses

Nucleoside modified mRNA combined with Acuitas Therapeutics' lipid nanoparticles (LNP) have been shown to support robust humoral immune responses in many preclinical animal vaccine studies and later in humans with the SARS-CoV-2 vaccination. We recently showed that this platform is highly inflammatory due to the LNPs' ionizable lipid component. The inflammatory property is key to support the development of potent humoral immune responses. However, the mechanism by which this platform drives T follicular helper cells (Tfh) and humoral immune responses remains unknown. Here we show that lack of Langerhans cells or cDC1s neither significantly affected the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cells and humoral immune responses, nor susceptibility towards the lethal challenge of influenza and SARS-CoV-2. However, the combined deletion of these two DC subsets led to a significant decrease in the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cell and humoral immune responses. Despite these observed defects, the still high antibody titers were sufficient to confer protection towards lethal viral challenges. We further found that IL-6, but not neutrophils, was required to generate Tfh cells and antibody responses. In summary, here we bring evidence that the mRNA-LNP platform can support protective adaptive immune responses in the absence of specific DC subsets through an IL-6 dependent and neutrophil independent mechanism.

Coronavirus infection: An immunologists' perspective

Coronavirus infections are frequent viral infections in several species. As soon as the severe acute respiratory syndrome (SARS) appeared in the early 2000s, most of the research focused on pulmonary disease. However, disorders in immune response and organ dysfunctions have been documented. Elderly individuals with comorbidities exhibit worse outcomes in all the coronavirus that cause SARS. Disease severity in SARS-CoV-2 infection is related to severe inflammation and tissue injury, and effective immune response against the virus is still under analysis. ACE2 receptor expression and polymorphism, age, gender and immune genetics are factors that also play an essential role in patients' clinical features and immune responses and have been partially discussed. The present report aims to review the physiopathology of SARS-CoV-2 infection and propose new research topics to understand the complex mechanisms of viral infection and viral clearance.

Endothelial Dysfunction and SARS-CoV-2 Infection: Association and Therapeutic Strategies

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), has been recently considered a systemic disorder leading to the procoagulant state. Preliminary studies have shown that SARS-CoV-2 can infect endothelial cells, and extensive evidence of inflammation and endothelial dysfunction has been found in advanced COVID-19. Endothelial cells play a critical role in many physiological processes, such as controlling blood fluidity, leukocyte activation, adhesion, platelet adhesion and aggregation, and transmigration. Therefore, it is reasonable to think that endothelial dysfunction leads to vascular dysfunction, immune thrombosis, and inflammation associated with COVID-19. This article summarizes the association of endothelial dysfunction and SARS-CoV-2 infection and its therapeutic strategies.

COVID-19 and Cardiovascular Disease: From Bench to Bedside

A pandemic of historic impact, coronavirus disease 2019 (COVID-19) has potential consequences on the cardiovascular health of millions of people who survive infection worldwide. Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), the etiologic agent of COVID-19, can infect the heart, vascular tissues, and circulating cells through ACE2 (angiotensin-converting enzyme 2), the host cell receptor for the viral spike protein. Acute cardiac injury is a common extrapulmonary manifestation of COVID-19 with potential chronic consequences. This update provides a review of the clinical manifestations of cardiovascular involvement, potential direct SARS-CoV-2 and indirect immune response mechanisms impacting the cardiovascular system, and implications for the management of patients after recovery from acute COVID-19 infection.

SARS-CoV-2 mediated neuroinflammation and the impact of COVID-19 in neurological disorders

SARS-CoV-2 is a novel coronavirus that severely affects the respiratory system, is the cause of the COVID-19 pandemic, and is projected to result in the deaths of 2 million people worldwide. Recent reports suggest that SARS-CoV-2 also affects the central nervous system along with other organs. COVID-19-associated complications are observed in older people with underlying neurological conditions like stroke, Alzheimer's disease, and Parkinson's disease. Hence, we discuss SARS-CoV-2 viral replication and its inflammation-mediated infection. This review also focuses on COVID-19 associated neurological complications in individuals with those complications as well as other groups of people. Finally, we also briefly discuss the current therapies available to treat patients, as well as ongoing available treatments and vaccines for effective cures with a special focus on the therapeutic potential of a small 5 amino acid peptide (PHSCN), ATN-161, that inhibits SARS-CoV-2 spike protein binding to both integrin α5β1 and α5β1/hACE2.

Role of the Immune Microenvironment in SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) first emerged in December 2019 in Wuhan, China, and has since spread rapidly worldwide. As researchers seek to learn more about COVID-19, the disease it causes, this novel virus continues to infect and kill. Despite the socioeconomic impacts of SARS-CoV-2 infections and likelihood of future outbreaks of other pathogenic coronaviruses, options to prevent or treat coronavirus infections remain limited. In current clinical trials, potential coronavirus treatments focusing on killing the virus or on preventing infection using vaccines largely ignore the host immune response. The relatively small body of current research on the virus indicates pathological responses by the immune system as the leading cause for much of the morbidity and mortality caused by COVID-19. In this review, we investigated the host innate and adaptive immune responses against COVID-19, collated information on recent COVID-19 experimental data, and summarized the systemic immune responses to and histopathology of SARS-CoV-2 infection. Finally, we summarized the immune-related biomarkers to define patients with high-risk and worst-case outcomes, and identified the possible usefulness of inflammatory markers as potential immunotherapeutic targets. This review provides an overview of current knowledge on COVID-19 and the symptomatological differences between healthy, convalescent, and severe cohorts, while offering research directions for alternative immunoregulation therapeutic targets.