Effect of SARS-CoV-2 S protein on the proteolytic cleavage of the epithelial Na+ channel ENaC.

Severe cases of COVID-19 are characterized by development of acute respiratory distress syndrome (ARDS). Water accumulation in the lungs is thought to occur as consequence of an exaggerated inflammatory response. A possible mechanism could involve decreased activity of the epithelial Na+ channel, ENaC, expressed in type II pneumocytes. Reduced transepithelial Na+ reabsorption could contribute to lung edema due to reduced alveolar fluid clearance. This hypothesis is based on the observation of the presence of a novel furin cleavage site in the S protein of SARS-CoV-2 that is identical to the furin cleavage site present in the alpha subunit of ENaC. Proteolytic processing of αENaC by furin-like proteases is essential for channel activity. Thus, competition between S protein and αENaC for furin-mediated cleavage in SARS-CoV-2-infected cells may negatively affect channel activity. Here we present experimental evidence showing that coexpression of the S protein with ENaC in a cellular model reduces channel activity. In addition, we show that bidirectional competition for cleavage by furin-like proteases occurs between 〈ENaC and S protein. In transgenic mice sensitive to lethal SARS-CoV-2, however, a significant decrease in gamma ENaC expression was not observed by immunostaining of lungs infected as shown by SARS-CoV2 nucleoprotein staining.

Immunomodulatory Activity of Diterpenes over Innate Immunity and Cytokine Production in a Human Alveolar Epithelial Cell Line Infected with Mycobacterium tuberculosis.

BACKGROUND: Mexico has the largest number of the genus salvia plant species, whose main chemical compounds of this genus are diterpenes, these chemical compounds have shown important biological activities such as: antimicrobial, anti-inflammatory and immunomodulatory. OBJECTIVE: This study aimed to evaluate the immunomodulatory activity of three diterpenes: 1) icetexone, 2) anastomosine and 3) 7,20-dihydroanastomosine, isolated from Salvia ballotiflora, over innate immunity and cytokine production in a human alveolar epithelial cell line infected with Mycobacterium tuberculosis. METHODS: The immunomodulatory activity of diterpenes over innate immunity included reactive oxygen and nitrogen species (ROS and RNS) induction in response to infection; cytokine production included TNF-α and TGF-ß induction in response to infection. RESULTS: The diterpenes anastomosine and 7,20-dihydroanastomosine showed a statically significant (p < 0.01) increase of RNS after 36 h of infection and treatment of 2.0 µg/mL. Then, the ROS induction in response to infection showed a consistent statically significant (p < 0.01) increase after 12 h of diterpenes treatments. The cell cultures showed an anti-inflammatory effect, in the case of TGF-ß induction, in response to infection when treated with the diterpenes. On the other hand, there was not any significant effect on TNF-α release. CONCLUSION: The diterpenes anastomosine and 7,20-dihydroanastomosine increased the production of RNS after 36 h of infection and treatment. Besides, the three diterpenes increased the production of ROS after 12 h. This RNS and ROS modulation can be considered as an in vitro correlation of innate immunity in response to Mycobacterium tuberculosis infection; and an indicator of the damage of epithelial lung tissue. This study also showed an anti-inflammatory immune response by means of TGF-ß modulation when compared with control group.

Swertiamarin attenuates paraquat-induced pulmonary epithelial-like cell apoptosis via NOX4-mediated regulation of redox and mitochondrial function

Abstract The aim of the present study was to investigate the effect of swertiamarin (STM) in attenuating paraquat (PQ)-induced human lung alveolar epithelial-like cell (A549) apoptosis and the underlying mechanisms. A549 cells were pretreated with different concentrations of STM for 2 hr and then cultured with or without PQ (700 µM) for 24 hr. Cell survival was determined using the CCK8 assay. Morphological changes, MDA content, inflammatory factors, fibrogenesis parameters, apoptosis rates, redox status and mitochondrial membrane potential (MMP) were evaluated. The expression of several genes involved in the modulation of redox status was measured by Western blotting. Cell viability and MMP were decreased, but the apoptosis rate and DCFH oxidation were elevated by PQ exposure. STM pretreatment notably increased cell viability and MMP and reduced the apoptosis rate and DCFH oxidation. Furthermore, TLR4- NOX4 signaling was significantly inhibited by STM. The downregulation of NOX4 by siRNA exerted the same protective effects as STM. This study provides the first evidence that STM attenuates PQ-induced pulmonary epithelial-like cell apoptosis via NOX4-mediated regulation of redox and mitochondrial function

Unlike Chloroquine, Mefloquine Inhibits SARS-CoV-2 Infection in Physiologically Relevant Cells.

Despite the development of specific therapies against severe acute respiratory coronavirus 2 (SARS-CoV-2), the continuous investigation of the mechanism of action of clinically approved drugs could provide new information on the druggable steps of virus-host interaction. For example, chloroquine (CQ)/hydroxychloroquine (HCQ) lacks in vitro activity against SARS-CoV-2 in TMPRSS2-expressing cells, such as human pneumocyte cell line Calu-3, and likewise, failed to show clinical benefit in the Solidarity and Recovery clinical trials. Another antimalarial drug, mefloquine, which is not a 4-aminoquinoline like CQ/HCQ, has emerged as a potential anti-SARS-CoV-2 antiviral in vitro and has also been previously repurposed for respiratory diseases. Here, we investigated the anti-SARS-CoV-2 mechanism of action of mefloquine in cells relevant for the physiopathology of COVID-19, such as Calu-3 cells (that recapitulate type II pneumocytes) and monocytes. Molecular pathways modulated by mefloquine were assessed by differential expression analysis, and confirmed by biological assays. A PBPK model was developed to assess mefloquine's optimal doses for achieving therapeutic concentrations. Mefloquine inhibited SARS-CoV-2 replication in Calu-3, with an EC50 of 1.2 µM and EC90 of 5.3 µM. It reduced SARS-CoV-2 RNA levels in monocytes and prevented virus-induced enhancement of IL-6 and TNF-α. Mefloquine reduced SARS-CoV-2 entry and synergized with Remdesivir. Mefloquine's pharmacological parameters are consistent with its plasma exposure in humans and its tissue-to-plasma predicted coefficient points suggesting that mefloquine may accumulate in the lungs. Altogether, our data indicate that mefloquine's chemical structure could represent an orally available host-acting agent to inhibit virus entry.

Renin-angiotensin system blockade on angiotensin-converting enzyme 2 and TMPRSS2 in human type II pneumocytes.

AIMS: Angiotensin-converting enzyme (ACE) 2 is the receptor for severe acute respiratory syndrome coronavirus 2 which causes coronavirus disease 2019 (COVID-19). Viral cellular entry requires ACE2 and transmembrane protease serine 2 (TMPRSS2). ACE inhibitors (ACEIs) or angiotensin (Ang) receptor blockers (ARBs) influence ACE2 in animals, though evidence in human lungs is lacking. We investigated ACE2 and TMPRSS2 in type II pneumocytes, the key cells that maintain lung homeostasis, in lung parenchymal of ACEI/ARB-treated subjects compared to untreated control subjects. MAIN METHODS: Ang II and Ang-(1-7) levels and ACE2 and TMPRSS2 protein expression were measured by radioimmunoassay and immunohistochemistry, respectively. KEY FINDINGS: We found that the ratio Ang-(1-7)/Ang II, a surrogate marker of ACE2 activity, as well as the amount of ACE2-expressing type II pneumocytes were not different between ACEI/ARB-treated and untreated subjects. ACE2 protein content correlated positively with smoking habit and age. The percentage of TMPRSS2-expressing type II pneumocytes was higher in males than females and in subjects under 60 years of age but it was not different between ACEI/ARB-treated and untreated subjects. However, there was a positive association of TMPRSS2 protein content with age and smoking in ACEI/ARB-treated subjects, with high TMPRSS2 protein levels most evident in ACEI/ARB-treated older adults and smokers. SIGNIFICANCE: ACEI/ARB treatment influences human lung TMPRSS2 but not ACE2 protein content and this effect is dependent on age and smoking habit. This finding may help explain the increased susceptibility to COVID-19 seen in smokers and older patients with treated cardiovascular-related pathologies.

Two-Step In Vitro Model to Evaluate the Cellular Immune Response to SARS-CoV-2.

The cellular immune response plays an important role in COVID-19, caused by SARS-CoV-2. This feature makes use of in vitro models' useful tools to evaluate vaccines and biopharmaceutical effects. Here, we developed a two-step model to evaluate the cellular immune response after SARS-CoV-2 infection-induced or spike protein stimulation in peripheral blood mononuclear cells (PBMC) from both unexposed and COVID-19 (primo-infected) individuals (Step1). Moreover, the supernatants of these cultures were used to evaluate its effects on lung cell lines (A549) (Step2). When PBMC from the unexposed were infected by SARS-CoV-2, cytotoxic natural killer and nonclassical monocytes expressing inflammatory cytokines genes were raised. The supernatant of these cells can induce apoptosis of A549 cells (mock vs. Step2 [mean]: 6.4% × 17.7%). Meanwhile, PBMCs from primo-infected presented their memory CD4+ T cells activated with a high production of IFNG and antiviral genes. Supernatant from past COVID-19 subjects contributed to reduce apoptosis (mock vs. Step2 [ratio]: 7.2 × 1.4) and to elevate the antiviral activity (iNOS) of A549 cells (mock vs. Step2 [mean]: 31.5% × 55.7%). Our findings showed features of immune primary cells and lung cell lines response after SARS-CoV-2 or spike protein stimulation that can be used as an in vitro model to study the immunity effects after SARS-CoV-2 antigen exposure.

TLR-9 Plays a Role in Mycobacterium leprae-Induced Innate Immune Activation of A549 Alveolar Epithelial Cells.

The respiratory tract is considered the main port of entry of Mycobacterium leprae, the causative agent of leprosy. However, the great majority of individuals exposed to the leprosy bacillus will never manifest the disease due to their capacity to develop protective immunity. Besides acting as a physical barrier, airway epithelium cells are recognized as key players by initiating a local innate immune response that orchestrates subsequent adaptive immunity to control airborne infections. However, to date, studies exploring the interaction of M. leprae with the respiratory epithelium have been scarce. In this work, the capacity of M. leprae to immune activate human alveolar epithelial cells was investigated, demonstrating that M. leprae-infected A549 cells secrete significantly increased IL-8 that is dependent on NF-κB activation. M. leprae was also able to induce IL-8 production in human primary nasal epithelial cells. M. leprae-treated A549 cells also showed higher expression levels of human ß-defensin-2 (hßD-2), MCP-1, MHC-II and the co-stimulatory molecule CD80. Furthermore, the TLR-9 antagonist inhibited both the secretion of IL-8 and NF-κB activation in response to M. leprae, indicating that bacterial DNA sensing by this Toll-like receptor constitutes an important innate immune pathway activated by the pathogen. Finally, evidence is presented suggesting that extracellular DNA molecules anchored to Hlp, a histone-like protein present on the M. leprae surface, constitute major TLR-9 ligands triggering this pathway. The ability of M. leprae to immune activate respiratory epithelial cells herein demonstrated may represent a very early event during infection that could possibly be essential to the generation of a protective response.

Inflammatory response in human alveolar epithelial cells after TiO2 NPs or ZnO NPs exposure: Inhibition of surfactant protein A expression as an indicator for loss of lung function.

The increasing use of metal oxide nanoparticles (MONPs) as TiO2 NPs or ZnO NPs has led to environmental release and human exposure. The respiratory system, effects on lamellar bodies and surfactant protein A (SP-A) of pneumocytes, can be importantly affected. Exposure of human alveolar epithelial cells (A549) induced differential responses; a higher persistence of TiO2 in cell surface and uptake (measured by Atomic Force Microscopy) and sustained inflammatory response (by means of TNF-α, IL-10, and IL-6 release) and ROS generation were observed, whereas ZnO showed a modest response and low numbers in cell surface. A reduction in SP-A levels at 24 h of exposure to TiO2 NPs (concentration-dependent) or ZnO NPs (the higher concentration) was also observed, reversed by blocking the inflammatory response (by the inhibition of IL-6). Loss of SP-A represents a relevant target of MONPs-induced inflammatory response that could contribute to cellular damage and loss of lung function.

Transbronchial biopsies' histopathological findings leading to successful late steroid therapy in Covid-19 acute respiratory failure.

We present results from clinical, radiologic, gas exchange, lung mechanics, and fibre-optic bronchoscopy-guided transbronchial biopsies in a case of acute respiratory failure due to SARS-CoV-2 (Covid-19). This report highlights the pulmonary, immunological, and inflammatory changes found during acute diffuse alveolar damage and the later organizing phase. An early diffuse alveolar damage pattern with predominant epithelial involvement with active recruitment of T cells and monocytes was observed followed by a late organizing pattern with pneumocyte hyperplasia, inflammatory infiltration, prominent endotheliitis, and secondary germinal centers. The patient's deterioration paralleling the late immuno-pathological findings based the decision to administer intravenous corticosteroids, resulting in clinical, gasometric, and radiologic improvement. We believe that real-time clinicopathological correlation, along with the description of the immunological processes at play, will contribute to the full clinical picture of Covid-19 and might lead to a more rational approach in the precise timing of anti-inflammatory, anti-cytokine, or steroid therapies.

Low-dose chlorine exposure impairs lung function, inflammation and oxidative stress in mice.

AIM: To explore the different consequences of acute and chronic exposure to chlorine gas (Cl2) on the functional and histological parameters of health mice. MAIN METHODS: Firstly, male BALB/c mice were acute exposed to 3.3 or 33.3 or 70.5 mg/m3 Cl2. We analyzed the lung function, the inflammatory cells in the bronchoalveolar lavage, cell influx in the peribrochoalveolar space and mucus production. In a second phase, mice were chronic exposed to 70.5 mg/m3 Cl2. Besides the first phase analyses, we also evaluated the epithelial cells thickness, collagen deposition in the airways, immunohistochemistry stain for IL-1ß, iNOS, IL-17 and ROCK-2 and the levels of IL-5, IL-13, IL-17, IL-1ß and TNF-α in lung homogenate. KEY FINDINGS: Acute exposure to chlorine impaired the lung function, increased the number of inflammatory cells in the BALF and in the airways, also increased the mucus production. Furthermore, when chlorine was exposed chronically, increased the airway remodeling with collagen deposition and epithelial cells thickness, positive cells for IL-1ß, iNOS, IL-17 in the airways and in the alveolar walls and ROCK-2 in the alveolar walls, lung inflammation with increased levels of IL-5, IL-13, IL-1ß and TNF-α in the lung homogenate, and also, induced the acid mucus production by the nasal epithelium. SIGNIFICANCE: Acute and chronic exposure to low dose of chlorine gas worsens lung function, induces oxidative stress activation and mucus production and contributes to augmenting inflammation in health mice.

In vitro cytotoxicity study of superparamagnetic iron oxide and silica nanoparticles on pneumocyte organelles.

Inhalation is the main route of nanoparticles (NP) exposure during manufacturing. Although many mechanisms of toxicity have been described, the interaction of NP with relevant pneumocytes organelles is not widely understood. Considering that the physicochemical properties of NP influence their toxicological responses, the objective of this study was to evaluate whether exposure to different NP, crystalline Fe3O4 NP and amorphous SiO2 NP could alter pneumocytes organelles in alveolar epithelial cells. To achieve this goal, cell viability, ultrastructural changes, lysosomal damage, mitochondrial membrane potential (MMP), lipid droplets (LD) formation and cytokines production were evaluated by MTT, electron microscopy, lysotracker red staining, JC-1, Oil Red staining and Milliplex® assay respectively. Both NP were observed within lamellar bodies (LB), lysosomes, and cytoplasm causing morphological changes. Exposure to SiO2 NP at 6 h induced lysosomal activation, but not Fe3O4 NP. MMP decreased and LD increased at the highest concentrations after both NP exposure. Pro-inflammatory cytokines were released only after SiO2 NP exposure at 48 h. These results indicate that SiO2 NP have a greater impact than Fe3O4 NP on organelles responsible for energy, secretion, degradation and metabolism in pneumocytes leading to the development of respiratory disorders or the exacerbation of preexisting conditions. Therefore, the established biocompatibility for amorphous NP has to be reconsidered.

Nicotine promotes the intracellular growth of Mycobacterium tuberculosis in epithelial cells.

Several epidemiological studies have identified the cigarette smoke as a risk factor for the infection and development of tuberculosis. Nicotine is considered the main immunomodulatory molecule of the cigarette. In the present study, we evaluated the effect of nicotine in the growth of M. tuberculosis. Lung epithelial cells and macrophages were infected with M. tuberculosis and/or treated with nicotine. The results show that nicotine increased the growth of M. tuberculosis mainly in type II pneumocytes (T2P) but not in airway basal epithelial cells nor macrophages. Further, it was observed that nicotine decreased the production of ß-defensin-2, ß-defensin-3, and the cathelicidin LL-37 in all the evaluated cells at 24 and 72 h post-infection. The modulation of the expression of antimicrobial peptides appears to be partially mediated by the nicotinic acetylcholine receptor α7 since the blockade of this receptor partially reverted the production of antimicrobial peptides. In summary, it was found that nicotine decreases the production of HBD-2, HBD-3, and LL-37 in T2P during the infection with M. tuberculosis promoting its intracellular growth.

TLR-9 Plays a Role in Mycobacterium leprae-Induced Innate Immune Activation of A549 Alveolar Epithelial Cells

The respiratory tract is considered the main port of entry of Mycobacterium leprae, the causative agent of leprosy. However, the great majority of individuals exposed to the leprosy bacillus will never manifest the disease due to their capacity to develop protective immunity. Besides acting as a physical barrier, airway epithelium cells are recognized as key players by initiating a local innate immune response that orchestrates subsequent adaptive immunity to control airborne infections. However, to date, studies exploring the interaction of M. leprae with the respiratory epithelium have been scarce. In this work, the capacity of M. leprae to immune activate human alveolar epithelial cells was investigated, demonstrating that M. leprae-infected A549 cells secrete significantly increased IL-8 that is dependent on NF-kB activation. M. leprae was also able to induce IL-8 production in human primary nasal epithelial cells. M. leprae-treated A549 cells also showed higher expression levels of human b-defensin-2 (hbD-2), MCP-1, MHC-II and the co-stimulatory molecule CD80. Furthermore, the TLR-9 antagonist inhibited both the secretion of IL-8 and NF-kB activation in response to M. leprae, indicating that bacterial DNA sensing by this Toll-like receptor constitutes an important innate immune pathway activated by the pathogen. Finally, evidence is presented suggesting that extracellular DNA molecules anchored to Hlp, a histone-like protein present on the M. leprae surface, constitute major TLR-9 ligands triggering this pathway. The ability of M. leprae to immune activate respiratory epithelial cells herein demonstrated may represent a very early event during infection that could possibly be essential to the generation of a protective response.(AU)

Surfactant in SARS-CoV-2 ­ a therapeutic option based on underlying lung cell damage? / Surfactante em SARS-CoV-2 ­ uma opção terapêutica baseada no dano celular subjacente aos pneumócitos?

Introduction: the severe acute respiratory syndrome ­ coronavirus 2 (SARS Cov-2), leads to a diffuse alveolar deterioration due infection of type II pneumocytes. The type II pneumocytes are involved in synthesis and secretion of pulmonary surfactant in pulmonary alveoli. Objective: the purpose of this study is to discuss the indication of surfactant replacement as a potential adjunctive treatment modality for SARS CoV-2, similarly treatment to neonatal respiratory distress syndrome. Methodology: we argue that SARS can be triggered by surfactant deficiency secondary to production deficiency determined by type 2 pneumocyte injuries. In this sense, we carried out a bibliographic review. Conclusion: thus, the replacement of human surfactant could be a potential treatment modality for SARS CoV-2, in the same way that it is indicated for the treatment of neonatal respiratory distress syndrome.

Introdução: a síndrome respiratória aguda grave ­ coronavírus 2 (SARS Cov-2), leva a uma deterioração alveolar difusa devido à infecção do pneumócitos tipo II. Os pneumócitos tipo II estão envolvidos na síntese e secreção de surfactante pulmonar nos alvéolos pulmonares. Objetivo: o objetivo deste estudo é discutir a indicação de reposição de surfactante como uma potencial modalidade de tratamento adjuvante para SARS CoV-2, similarmente ao tratamento da síndrome do desconforto respiratório neonatal. Metodologia: argumentamos que a SARS pode ser desencadeada pela deficiência de surfactante, secundária à deficiência da sua produção determinada por lesões de pneumócitos tipo 2. Nesse sentido, realizamos uma revisão bibliográfica. Conclusão: o uso de surfactante humana pode ser uma potencial modalidade de tratamento para a SARS CoV-2, da mesma forma que é indicada para o tratamento da síndrome do desconforto respiratório neonatal.

SARS-CoV-2: generalidades bioquímicas y métodos de diagnóstico / SARS-CoV-2: biochemical aspects and diagnostic methods

Resumen El 31 de diciembre de 2019 la comisión municipal de salud de Wuhan (provincia de Hubei, China) informa sobre un inusitado brote de casos de neumonía en la ciudad. Posteriormente se determina que se trata de un nuevo coronavirus designado inicialmente como 2019-nCoV y posteriormente, SARS-CoV-2. El SARS-CoV-2 infecta y se replica en los neumocitos y macrófagos del sistema respiratorio específicamente en el parénquima pulmonar en donde reside el receptor celular ACE-2. Esta revisión describe aspectos relacionados con la transmisión, prevención, generalidades bioquímicas del SARS-CoV-2 y métodos diagnósticos del COVID-19. Inicialmente se describe la forma de transmisión del virus y algunas recomendaciones generales para su prevención. Posteriormente, se hace una descripción detallada de los aspectos bioquímicos del SARS-CoV-2, su ciclo infeccioso y la estructura de la proteína S, la cual está involucrada con el proceso de ingreso del virus a la célula. Finalmente, se describen los métodos y pruebas de laboratorio para el diagnóstico del COVID-19.

Abstract On December 31, 2019, Wuhan Municipal Health Commission (Hubei Province, China) reports on an unusual outbreak of pneumonia cases in the city. Subsequently it is determined that it is a new coronavirus initially designated as 2019-nCoV and later, SARS-CoV-2. SARS-CoV-2 infects and replicates in pneumocytes and macrophages of the respiratory system specifically in the lung parenchyma where the ACE-2 cell receptor resides. This review describes aspects related to the transmission, prevention, biochemical generalities of SARS-CoV-2 and diagnostic methods of COVID-19. Initially, it describes the form of virus transmission and general recommendations for its prevention. Subsequently, a detailed description is made of the biochemical aspects of SARS-CoV-2, its infectious cycle and the structure of protein S, which is involved in the process of entry of the virus into the cell. Finally, the methods and laboratory tests for the diagnosis of COVID-19 are described.

Presencia y Expresión del Receptor ACE2 (Target de SARS-CoV-2) en Tejidos Humanos y Cavidad Oral. Posibles Rutas de Infección en Órganos Orales / Presence and Expression of ACE2 Receptor (Target of SARS-CoV-2) in Human Tissues and Oral Cavity. Possible Routes Infection in Oral Organs

RESUMEN: Un nuevo coronavirus (SARS-CoV-2) ha sido reconocido como el agente etiológico de una misteriosa neumonía originada en Wuhan, China. La OMS ha nombrado a la nueva enfermedad como COVID-19 y, además, la ha declarado pandemia. Taxonómicamente, SARS-CoV-2 pertenece al género de los betacoronavirus junto con SARS-CoV y MERS-CoV. SARS-CoV-2 utiliza la enzima convertidora de la angiotensina 2 (ACE2) como el receptor objetivo para el ingreso en una célula huésped. La expresión de ACE2 en células de tejidos humanos podría indicar un potencial riesgo de reconocimiento por parte del virus y, por ende, ser susceptibles a la infección. Mediante algunas técnicas de laboratorio y de bioinformática, se ha visto una alta presencia de ACE2 en células epiteliales alveolares tipo II de pulmón y en enterocitos del intestino delgado. En la cavidad oral, se ha podido identificar la presencia de ACE2, principalmente, en células epiteliale s de glándulas salivales y células epiteliales de la lengua. Además, se ha reportado la manifestación de algunos síntomas, como sequedad bucal y ambligeustia, los que podrían estar relacionadas con una infección de SARS-CoV-2 en estos órganos. Sin embargo, son necesarios mayores estudios que evidencien esta situación.

ABSTRACT: A novel coronavirus (SARS-CoV-2) has been recognized as a etiologic agent of a mysterious pneumonia originating in Wuhan, China. WHO has named the new disease as COVID-19 and, in addition, has declared it a pandemic. Taxonomically, SARS-CoV-2 belongs to the betacoronavirus genus along with SARS-CoV and MERS-CoV. SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as the target receptor for entry into a host cell. The expression of ACE2 in cells of human tissues could indicate a potential risk of recognition by the virus and, therefore, be susceptible to infection. Through some laboratory and bioinformatics techniques, high presence of ACE2 has been seen in type II alveolar epithelial cells of the lung and enterocytes of the small intestine. In oral cavity, mainly presence of ACE2 has been identified in epithelial cells of salivary glands and epithelial cells of tongue. In addition, manifestation of some symptoms, such as dry mouth and amblygeustia, have been reported, which could be related to a SARS-CoV-2 infection in these organs. However, further studies are needed to prove this situation.

Interplay between alveolar epithelial and dendritic cells and Mycobacterium tuberculosis.

The innate response plays a crucial role in the protection against tuberculosis development. Moreover, the initial steps that drive the host-pathogen interaction following Mycobacterium tuberculosis infection are critical for the development of adaptive immune response. As alveolar Mϕs, airway epithelial cells, and dendritic cells can sense the presence of M. tuberculosis and are the first infected cells. These cells secrete mediators, which generate inflammatory signals that drive the differentiation and activation of the T lymphocytes necessary to clear the infection. Throughout this review article, we addressed the interaction between epithelial cells and M. tuberculosis, as well as the interaction between dendritic cells and M. tuberculosis. The understanding of the mechanisms that modulate those interactions is critical to have a complete view of the onset of an infection and may be useful for the development of dendritic cell-based vaccine or immunotherapies.

Mycobacterium tuberculosis-infected alveolar epithelial cells modulate dendritic cell function through the HIF-1α-NOS2 axis.

Tuberculosis kills more than 1 million people every year, and its control depends on the effective mechanisms of innate immunity, with or without induction of adaptive immune response. We investigated the interaction of type II alveolar epithelial cells (AEC-II) infected by Mycobacterium tuberculosis with dendritic cells (DCs). We hypothesized that the microenvironment generated by this interaction is critical for the early innate response against mycobacteria. We found that AEC-II infected by M. tuberculosis induced DC maturation, which was negatively regulated by HIF-1α-inducible NOS2 axis, and switched DC metabolism from an early and short peak of glycolysis to a low energetic status. However, the infection of DCs by M. tuberculosis up-regulated NOS2 expression and inhibited AEC-II-induced DC maturation. Our study demonstrated, for the first time, that HIF-1α-NOS2 axis plays a negative role in the maturation of DCs during M. tuberculosis infection. Such modulation might be useful for the exploitation of molecular targets to develop new therapeutic strategies against tuberculosis.

Histoplasma capsulatum chemotypes I and II induce IL-8 secretion in lung epithelial cells in distinct manners.

The cell wall is one of the most important structures of pathogenic fungi, enabling initial interaction with the host and consequent modulation of immunological responses. Over the years, some researchers have shown that cell wall components of Histoplasma capsulatum vary among fungal isolates, and one of the major differences is the presence or absence of α-(1,3)-glucan, classifying wild-type fungi as chemotypes II or I, respectively. The present work shows that an isolate of H. capsulatum chemotype I induced lower levels of interleukin (IL)-8 secretion by the lung epithelial cell line A549, when compared to chemotype II yeasts. Thus, we expected that the absence of α-glucan in spontaneous variant yeasts, which were isolated from chemotype II cultures, would modify IL-8 secretion by A549 cells, but surprisingly, these fungi promoted similar levels of IL-8 secretion as their wild-type counterpart. Furthermore, when using a specific inhibitor for Syk activation, we observed that this inhibitor reduced IL-8 levels in A549 cell cultures infected with wild type chemotype I fungi. This inhibitor failed to reduce this cytokine levels in A549 cell cultures infected with chemotype II and their spontaneous variant yeasts, which also do not present α-glucan on their surface. The importance of SFKs and PKC δ in this event was also analyzed. Our results show that different isolates of H. capsulatum modulate distinct cell signaling pathways to promote cytokine secretion in host epithelial cells, emphasizing the existence of various mechanisms for Histoplasma pathogenicity.