A model for COVID-19-induced dysregulation of ACE2 shedding by ADAM17

JG26 attenuates ADAM17 metalloproteinase-mediated ACE2 receptor processing and SARS-CoV-2 infection in vitro

BACKGROUND

ADAM17 is a metalloprotease implicated in the proteolysis of angiotensin-converting enzyme 2 (ACE2), known to play a critical role in the entry and spread of SARS-CoV-2. In this context, ADAM17 results as a potential novel target for controlling SARS-CoV-2 infection.

METHODS

In this study, we investigated the impact on ACE2 surface expression and the antiviral efficacy against SARS-CoV-2 infection of the selective ADAM17 inhibitor JG26 and its dimeric (compound 1) and glycoconjugate (compound 2) derivatives using Calu-3 human lung cells.

RESULTS

None of the compounds exhibited cytotoxic effects on Calu-3 cells up to a concentration of 25 µM. Treatment with JG26 resulted in partial inhibition of both ACE2 receptor shedding and SARS-CoV-2 infection, followed by compound 1.

CONCLUSION

JG26, an ADAM17 inhibitor, demonstrated promising antiviral activity against SARS-CoV-2 infection, likely attributed to reduced sACE2 availability, thus limiting viral dissemination.

Density functional theory and enzyme studies support interactions between angiotensin receptor blockers and angiotensin converting enzyme-2: Relevance to coronavirus 2019

The binding affinities and interactions between eight drug candidates, both commercially available (candesartan; losartan; losartan carboxylic acid; nirmatrelvir; telmisartan) and newly synthesized benzimidazole-N-biphenyltetrazole (ACC519T), benzimidazole bis-N,N'-biphenyltetrazole (ACC519T(2) and 4-butyl-N,N-bis([2-(2H-tetrazol-5-yl)biphenyl-4-yl]) methyl (BV6), and the active site of angiotensin-converting enzyme-2 (ACE2) were evaluated for their potential as inhibitors against SARS-CoV-2 and regulators of ACE2 function through Density Functional Theory methodology and enzyme activity assays, respectively. Notably, telmisartan and ACC519T(2) exhibited pronounced binding affinities, forming strong interactions with ACE2's active center, favorably accepting proton from the guanidinium group of arginine273. The ordering of candidates by binding affinity and reactivity descriptors, emerged as telmisartan > ACC519T(2) > candesartan > ACC519T > losartan carboxylic acid > BV6 > losartan > nirmatrelvir. Proton transfers among the active center amino acids revealed their interconnectedness, highlighting a chain-like proton transfer involving tyrosine, phenylalanine, and histidine. Furthermore, these candidates revealed their potential antiviral abilities by influencing proton transfer within the ACE2 active site. Furthermore, through an in vitro pharmacological assays we determined that candesartan and the BV6 derivative, 4-butyl-N,N0-bis[20-2Htetrazol-5-yl)bipheyl-4-yl]methyl)imidazolium bromide (BV6(K+)2) also contain the capacity to increase ACE2 functional activity. This comprehensive analysis collectively underscores the promise of these compounds as potential therapeutic agents against SARS-CoV-2 by targeting crucial protein interactions.

Aprotinin (I): Understanding the Role of Host Proteases in COVID-19 and the Importance of Pharmacologically Regulating Their Function

Proteases are produced and released in the mucosal cells of the respiratory tract and have important physiological functions, for example, maintaining airway humidification to allow proper gas exchange. The infectious mechanism of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), takes advantage of host proteases in two ways: to change the spatial conformation of the spike (S) protein via endoproteolysis (e.g., transmembrane serine protease type 2 (TMPRSS2)) and as a target to anchor to epithelial cells (e.g., angiotensin-converting enzyme 2 (ACE2)). This infectious process leads to an imbalance in the mucosa between the release and action of proteases versus regulation by anti-proteases, which contributes to the exacerbation of the inflammatory and prothrombotic response in COVID-19. In this article, we describe the most important proteases that are affected in COVID-19, and how their overactivation affects the three main physiological systems in which they participate: the complement system and the kinin-kallikrein system (KKS), which both form part of the contact system of innate immunity, and the renin-angiotensin-aldosterone system (RAAS). We aim to elucidate the pathophysiological bases of COVID-19 in the context of the imbalance between the action of proteases and anti-proteases to understand the mechanism of aprotinin action (a panprotease inhibitor). In a second-part review, titled "Aprotinin (II): Inhalational Administration for the Treatment of COVID-19 and Other Viral Conditions", we explain in depth the pharmacodynamics, pharmacokinetics, toxicity, and use of aprotinin as an antiviral drug.

The rs11684747 and rs55790676 SNPs of ADAM17 influence tuberculosis susceptibility and plasma levels of TNF, TNFR1, and TNFR2

Introduction

The proteolytic activity of A Disintegrin and Metalloproteinase 17 (ADAM17) regulates the release of tumor necrosis factor (TNF) and TNF receptors (TNFRs) from cell surfaces. These molecules play important roles in tuberculosis (TB) shaping innate immune reactions and granuloma formation.

Methods

Here, we investigated whether single nucleotide polymorphisms (SNPs) of ADAM17 influence TNF and TNFRs levels in 224 patients with active TB (ATB) and 118 healthy close contacts. Also, we looked for significant associations between SNPs of ADAM17 and ATB status. TNF, TNFR1, and TNFR2 levels were measured in plasma samples by ELISA. Four SNPs of ADAM17 (rs12692386, rs1524668, rs11684747, and rs55790676) were analyzed in DNA isolated from peripheral blood leucocytes. The association between ATB status, genotype, and cytokines was analyzed by multiple regression models.

Results

Our results showed a higher frequency of rs11684747 and rs55790676 in close contacts than ATB patients. Coincidentally, heterozygous to these SNPs of ADAM17 showed higher plasma levels of TNF compared to homozygous to their respective ancestral alleles. Strikingly, the levels of TNF and TNFRs distinguished participant groups, with ATB patients displaying lower TNF and higher TNFR1/TNFR2 levels compared to their close contacts.

Conclusion

These findings suggest a role for SNPs of ADAM17 in genetic susceptibility to ATB.

Combination of spironolactone and DPP-4 inhibitors for treatment of SARS-CoV-2 infection: a literature review

Coronavirus disease 2019 (COVID-19) is still causing hospitalization and death, and vaccination appears to become less effective with each emerging variant. Spike, non-spike, and other possible unrecognized mutations have reduced the efficacy of recommended therapeutic approaches, including monoclonal antibodies, plasma transfusion, and antivirals. SARS-CoV-2 binds to angiotensin-converting enzyme 2 (ACE2) and probably dipeptidyl peptidase 4 (DPP-4) to initiate the process of endocytosis by employing host proteases such as transmembrane serine protease-2 (TMPRSS-2) and ADAM metallopeptidase domain 17 (ADAM17). Spironolactone reduces the amount of soluble ACE2 and antagonizes TMPRSS-2 and ADAM17. DPP-4 inhibitors play immunomodulatory roles and may block viral entry. The efficacy of treatment with a combination of spironolactone and DPP-4 inhibitors does not appear to be affected by viral mutations. Therefore, the combination of spironolactone and DPP-4 inhibitors might improve the clinical outcome for COVID-19 patients by decreasing the efficiency of SARS-CoV-2 entry into cells and providing better anti-inflammatory, antiproliferative, and antifibrotic effects than those achieved using current therapeutic approaches such as antivirals and monoclonal antibodies.

Involvement of Matrix Metalloproteinases in COVID-19: Molecular Targets, Mechanisms, and Insights for Therapeutic Interventions

MMPs are enzymes involved in SARS-CoV-2 pathogenesis. Notably, the proteolytic activation of MMPs can occur through angiotensin II, immune cells, cytokines, and pro-oxidant agents. However, comprehensive information regarding the impact of MMPs in the different physiological systems with disease progression is not fully understood. In the current study, we review the recent biological advances in understanding the function of MMPs and examine time-course changes in MMPs during COVID-19. In addition, we explore the interplay between pre-existing comorbidities, disease severity, and MMPs. The reviewed studies showed increases in different MMP classes in the cerebrospinal fluid, lung, myocardium, peripheral blood cells, serum, and plasma in patients with COVID-19 compared to non-infected individuals. Individuals with arthritis, obesity, diabetes, hypertension, autoimmune diseases, and cancer had higher MMP levels when infected. Furthermore, this up-regulation may be associated with disease severity and the hospitalization period. Clarifying the molecular pathways and specific mechanisms that mediate MMP activity is important in developing optimized interventions to improve health and clinical outcomes during COVID-19. Furthermore, better knowledge of MMPs will likely provide possible pharmacological and non-pharmacological interventions. This relevant topic might add new concepts and implications for public health in the near future.

Role of Angiotensin II in Cardiovascular Diseases: Introducing Bisartans as a Novel Therapy for Coronavirus 2019

Cardiovascular diseases (CVDs) are the main contributors to global morbidity and mortality. Major pathogenic phenotypes of CVDs include the development of endothelial dysfunction, oxidative stress, and hyper-inflammatory responses. These phenotypes have been found to overlap with the pathophysiological complications of coronavirus disease 2019 (COVID-19). CVDs have been identified as major risk factors for severe and fatal COVID-19 states. The renin-angiotensin system (RAS) is an important regulatory system in cardiovascular homeostasis. However, its dysregulation is observed in CVDs, where upregulation of angiotensin type 1 receptor (AT1R) signaling via angiotensin II (AngII) leads to the AngII-dependent pathogenic development of CVDs. Additionally, the interaction between the spike protein of severe acute respiratory syndrome coronavirus 2 with angiotensin-converting enzyme 2 leads to the downregulation of the latter, resulting in the dysregulation of the RAS. This dysregulation favors AngII/AT1R toxic signaling pathways, providing a mechanical link between cardiovascular pathology and COVID-19. Therefore, inhibiting AngII/AT1R signaling through angiotensin receptor blockers (ARBs) has been indicated as a promising therapeutic approach to the treatment of COVID-19. Herein, we review the role of AngII in CVDs and its upregulation in COVID-19. We also provide a future direction for the potential implication of a novel class of ARBs called bisartans, which are speculated to contain multifunctional targeting towards COVID-19.

Highlights on molecular targets in the management of COVID-19: Possible role of pharmacogenomics

By the end of 2022, there had been a reduction in new cases and deaths caused by coronavirus disease 2019 (COVID-19). At the same time, new variants of the severe acute respiratory syndrome coronavirus 2 virus were being discovered. Critically ill patients with COVID-19 have been found to have high serum levels of proinflammatory cytokines, especially interleukin (IL)-6. COVID-19-related mortality has been attributed in most cases to the cytokine storm caused by increased levels of inflammatory cytokines. Dexamethasone in low doses and immunomodulators such as IL-6 inhibitors are recommended to overcome the cytokine storm. This current narrative review highlights the place of other therapeutic choices such as proteasome inhibitors, protease inhibitors and nuclear factor kappa B inhibitors in the treatment of patients with COVID-19.

Evaluation of the Relationship Between Serum miR-200b-3p and miR-214-3p Expression Levels with Soluble ACE2 and TMPRSS2 in COVID-19 Patients

Background

The emergence and rapid global spread of the coronavirus disease 2019 (COVID-19) has presented a significant global health challenge. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects human host cells through the interaction of angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2), which serve as main regulators for viral entry. Specifically, ACE2 and TMPRSS2 genes are influenced by two microRNAs: miR-200b-3p and miR-214-3p, respectively. The objective of this study was to explore the association between the serum levels of miR-200b-3p and miR-214-3p and the presence of circulating ACE2 and TMPRSS2 in severe and non-severe cases of COVID-19.

Objectives

This study sought to examine the potential utility of microRNAs as biomarkers for assessing disease severity and progression. Additionally, the study aimed to elucidate the interplay between microRNAs and the ACE2 and TMPRSS2 proteins, which play crucial roles in facilitating SARS-CoV-2 viral entry and infection.

Methods

This practical-foundational study involved the collection of samples from 61 hospitalized patients with confirmed COVID-19 and 31 healthy individuals. Subsequently, the enzyme-linked immunosorbent assay (ELISA) technique was utilized to measure the concentrations of ACE2 and TMPRSS2 in the blood samples. Additionally, the expression levels of serum miR-200b-3p and miR-214-3p were analyzed using real-time polymerase chain reaction (PCR). The statistical analysis of the data was conducted using GraphPad Prism software (version 8.02) and SPSS software (version 19.0), ensuring the accurate interpretation of results.

Results

The findings revealed significant increases in the peripheral blood concentrations of ACE2 and TMPRSS2 in patients with non-severe COVID-19, compared to healthy individuals (P < 0.001 and P < 0.01, respectively). Similarly, patients with severe COVID-19 exhibited higher serum levels of ACE2 and TMPRSS2 than healthy subjects (P < 0.0001). Additionally, the serum levels of miR-200b-3p and miR-214-3p were decreased in both non-severe and severe COVID-19 patients, compared to healthy individuals (P < 0.01 and P < 0.0001, respectively). Moreover, a decrease in the serum levels of both miR-200b-3p and miR-214-3p was observed in patients with severe COVID-19, compared to those with non-severe cases (P < 0.001). Furthermore, this study identified a negative correlation between miR-200b-3p and ACE2 serum levels and between miR-214-3p and TMPRSS2 peripheral blood levels.

Conclusions

The above-mentioned findings suggest that miR-200b-3p and miR-214-3p might be potential biomarkers for disease severity and prognosis in COVID-19 patients.

Antiviral Potential of Small Molecules Cordycepin, Thymoquinone, and N6, N6-Dimethyladenosine Targeting SARS-CoV-2 Entry Protein ADAM17

COVID-19 is an acute respiratory disease caused by SARS-CoV-2 that has spawned a worldwide pandemic. ADAM17 is a sheddase associated with the modulation of the receptor ACE2 of SARS-CoV-2. Studies have revealed that malignant phenotypes of several cancer types are closely relevant to highly expressed ADAM17. However, ADAM17 regulation in SARS-CoV-2 invasion and its role on small molecules are unclear. Here, we evaluated the ADAM17 inhibitory effects of cordycepin (CD), thymoquinone (TQ), and N6, N6-dimethyladenosine (m⁶₂A), on cancer cells and predicted the anti-COVID-19 potential of the three compounds and their underlying signaling pathways by network pharmacology. It was found that CD, TQ, and m⁶₂A repressed the ADAM17 expression upon different cancer cells remarkably. Moreover, CD inhibited GFP-positive syncytia formation significantly, suggesting its potential against SARS-CoV-2. Pharmacological analysis by constructing CD-, TQ-, and m⁶₂A-based drug-target COVID-19 networks further indicated that ADAM17 is a potential target for anti-COVID-19 therapy with these compounds, and the mechanism might be relevant to viral infection and transmembrane receptors-mediated signal transduction. These findings imply that ADAM17 is of potentially medical significance for cancer patients infected with SARS-CoV-2, which provides potential new targets and insights for developing innovative drugs against COVID-19.

Circulating angiotensin converting enzyme 2 and COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered a widespread outbreak since December 2019. The SARS-CoV-2 infection-related illness has been dubbed the coronavirus disease 2019 (COVID-19) by the World Health Organization. Asymptomatic and subclinical infections, a severe hyper-inflammatory state, and mortality are all examples of clinical signs. After attaching to the angiotensin converting enzyme 2 (ACE2) receptor, the SARS-CoV-2 virus can enter cells through membrane fusion and endocytosis. In addition to enabling viruses to cling to target cells, the connection between the spike protein (S-protein) of SARS-CoV-2 and ACE2 may potentially impair the functionality of ACE2. Blood pressure is controlled by ACE2, which catalyzes the hydrolysis of the active vasoconstrictor octapeptide angiotensin (Ang) II to the heptapeptide Ang-(1-7) and free L-Phe. Additionally, Ang I can be broken down by ACE2 into Ang-(1-9) and metabolized into Ang-(1-7). Numerous studies have demonstrated that circulating ACE2 (cACE2) and Ang-(1-7) have the ability to restore myocardial damage in a variety of cardiovascular diseases and have anti-inflammatory, antioxidant, anti-apoptotic, and anti-cardiomyocyte fibrosis actions. There have been some suggestions for raising ACE2 expression in COVID-19 patients, which might be used as a target for the creation of novel treatment therapies. With regard to this, SARS-CoV-2 is neutralized by soluble recombinant human ACE2 (hrsACE2), which binds the viral S-protein and reduces damage to a variety of organs, including the heart, kidneys, and lungs, by lowering Ang II concentrations and enhancing conversion to Ang-(1-7). This review aims to investigate how the presence of SARS-CoV-2 and cACE2 are related. Additionally, there will be discussion of a number of potential therapeutic approaches to tip the ACE/ACE-2 balance in favor of the ACE-2/Ang-(1-7) axis.

Immunomodulatory role of metalloproteinase ADAM17 in tumor development

ADAM17 is a member of the a disintegrin and metalloproteinase (ADAM) family of transmembrane proteases involved in the shedding of some cell membrane proteins and regulating various signaling pathways. More than 90 substrates are regulated by ADAM17, some of which are closely relevant to tumor formation and development. Besides, ADAM17 is also responsible for immune regulation and its substrate-mediated signal transduction. Recently, ADAM17 has been considered as a major target for the treatment of tumors and yet its immunomodulatory roles and mechanisms remain unclear. In this paper, we summarized the recent understanding of structure and several regulatory roles of ADAM17. Importantly, we highlighted the immunomodulatory roles of ADAM17 in tumor development, as well as small molecule inhibitors and monoclonal antibodies targeting ADAM17.

Association of COVID-19 with hepatic metabolic dysfunction

The coronavirus disease 2019 (COVID-19) pandemic continues to be a global problem with over 438 million cases reported so far. Although it mostly affects the respiratory system, the involvement of extrapulmonary organs, including the liver, is not uncommon. Since the beginning of the pandemic, metabolic com-orbidities, such as obesity, diabetes, hypertension, and dyslipidemia, have been identified as poor prognostic indicators. Subsequent metabolic and lipidomic studies have identified several metabolic dysfunctions in patients with COVID-19. The metabolic alterations appear to be linked to the course of the disease and inflammatory reaction in the body. The liver is an important organ with high metabolic activity, and a significant proportion of COVID-19 patients have metabolic comorbidities; thus, this factor could play a key role in orchestrating systemic metabolic changes during infection. Evidence suggests that metabolic dysregulation in COVID-19 has both short- and long-term metabolic implications. Furthermore, COVID-19 has adverse associations with metabolic-associated fatty liver disease. Due to the ensuing effects on the renin-angiotensin-aldosterone system and ammonia metabolism, COVID-19 can have significant implications in patients with advanced chronic liver disease. A thorough understanding of COVID-19-associated metabolic dysfunction could lead to the identification of important plasma biomarkers and novel treatment targets. In this review, we discuss the current understanding of metabolic dysfunction in COVID-19, focusing on the liver and exploring the underlying mechanistic pathogenesis and clinical implications.

Potential Similarities in Sex Difference in Key Genes and Their Expression, Network, EQTL and Pathways between COVID-19 and Chronic Kidney Disease Based on Mouse Model

COVID-19 and chronic kidney disease (CKD) share similarity in sex bias and key genes in the disease pathway of sex difference. We investigated the sex difference of molecular pathways of four key players of these two diseases using an existing large set of whole genome expression profiles from the kidneys of female and male mouse models. Our data show that there is little to no correlation at the whole genome expression level between female and male mice among these four genes. There are considerable sex differences among genes in upstream regulation, Ace2 complex interaction, and downstream pathways. Snap25 and Plcb4 may play important roles in the regulation of the expression level of Adam17, Tmprss2, and Cd146 in females. In males, Adh4 is a candidate gene for the regulation of Adam17, while Asl, Auts2, and Rabger1 are candidates for Tmprss2. Within the Ace2 complex, Cd146 directly influences the expression level of Adam17 and Ace2 in the female, while in the male Adam potentially has a stronger influence on Ace2 than that of Tmprss2. Among the top 100 most related genes, only one or two genes from four key genes and 11 from the control B-Actin were found to be the same between sexes. Among the top 10 sets of genes in the downstream pathway of Ace2, only two sets are the same between the sexes. We concluded that these known key genes and novel genes in CKD may play significant roles in the sex difference in the CKD and COVID-19 disease pathways.

The Correlation Between Immune Invasion and SARS-COV-2 Entry Protein ADAM17 in Cancer Patients by Bioinformatic Analysis

SARS-Cov-2 caused the COVID-19 pandemic worldwide. ADAM17 functions as a disintegrin and transmembrane metalloproteinase domain protein involved in the regulation of SARS-CoV-2 receptor ACE2. However, its impact on cancer patients infected with COVID-19 and its correlation with immune cell infiltration is unclear. This study compared ADAM17 expression between normal and tumor tissues based on GEPIA. The correlations between ADAM17 expression and immune cell infiltration and immunomodulators were investigated. Besides, treated drugs for targeting ADAM17 were searched in the TISDB database. We found that ADAM17 was highly conserved in many species and was mainly expressed in lung, brain, female tissues, bone marrow and lymphoid tissues. It was also highly expressed in respiratory epithelial cells of rhinitis and bronchus. ADAM17 expression in tumors was higher than that in several paired normal tissues and was negatively correlated with the prognosis of patients with malignant tumors. Interestingly, ADAM17 expression significantly correlated with immunomodulators and immune cell infiltration in normal and tumor tissues. Moreover, eight small molecules targeting ADAM17 only demonstrate therapeutic significance. These findings imply important implications for ADAM17 in cancer patients infected with COVID-19 and provide new clues for development strategy of anti-COVID-19.

The atlas of ACE2 expression in fetal and adult human hearts reveals the potential mechanism of heart injured patients infected with SARS-CoV-2

Numerous studies have shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect host cells through binding to angiotensin I converting enzyme 2 (ACE2) expressing in various tissues and organs. In this study, we deeply analyzed the single-cell expression profiles of ACE2 in fetal and adult human hearts to explore the potential mechanism of SARS-CoV-2 harming the heart. The molecular docking software was used to simulate the binding of SARS-CoV-2 and its variant spike protein with ACE2. The genes closely related to ACE2 in renin-angiotensin system (RAS) were identified by constructing a protein-protein interaction network. Through the analysis of single-cell transcription profiles at different stages of human embryos, we found that the expression level of ACE2 in ventricular myocytes was increased with embryonic development. The results of single-cell sequencing analysis showed that the expression of ACE2 in ventricular myocytes was upregulated in heart failure induced by dilated cardiomyopathy compared with normal hearts. The upregulation of ACE2 increases the risk of infection with SARS-CoV-2 in fetal and adult human hearts. We also further confirmed the expression of ACE2 and ACE2-related genes in normal and SARS-CoV-2-infected human pluripotent stem cell-derived cardiomyocytes. In addition, the pathway analysis revealed that ACE2 may regulate the differently expressed genes in heart failure through calcium signaling pathway and Wnt signaling pathway.

How tetraspanin-mediated cell entry of SARS-CoV-2 can dysregulate the shedding of the ACE2 receptor by ADAM17

COVID-19, the respiratory infection caused by the novel coronavirus SARS-CoV-2, presents a clinical picture consistent with the dysregulation of many of the pathways mediated by the metalloprotease ADAM17. ADAM17 is a sheddase that plays a key role in the modulation of ACE2, the receptor which also functions as the point of attachment leading to cell entry by the virus. This work investigates the possibility that ADAM17 dysregulation and attachment of the SARS-CoV-2 virion to the ACE2 receptor are linked events, with the latter causing the former. Tetraspanins, the transmembrane proteins that function as scaffolds for the construction of viral entry platforms, are mooted as key components in this connection.

Can bacterial lysates be useful in prevention of viral respiratory infections in childhood? The results of experimental OM-85 studies

Respiratory tract infections (RTI) are mainly viral in origin and among the leading cause of childhood morbidity globally. Associated wheezing illness and asthma are still a clear unmet medical need. Despite the continuous progress in understanding the processes involved in their pathogenesis, preventive measures and treatments failed to demonstrate any significant disease-modifying effect. However, in the last decades it was understood that early-life exposure to microbes, may reduce the risk of infectious and allergic disorders, increasing the immune response efficacy. These results suggested that treatment with bacterial lysates (BLs) acting on gut microbiota, could promote a heterologous immunomodulation useful in the prevention of recurrent RTIs and of wheezing inception and persistence. This hypothesis has been supported by clinical and experimental studies showing the reduction of RTI frequency and severity in childhood after oral BL prophylaxis and elucidating the involved mechanisms. OM-85 is the product whose anti-viral effects have been most extensively studied in vitro, animal, and human cell studies and in translational animal infection/disease models. The results of the latter studies, describing the potential immune training-based activities of such BL, leading to the protection against respiratory viruses, will be reported. In response to human rhinovirus, influenza virus, respiratory syncytial virus and severe acute respiratory coronavirus-2, OM-85 was effective in modulating the structure and the functions of a large numbers of airways epithelial and immune cells, when administered both orally and intranasally.