Intranasal administration of Escherichia coli Nissle expressing the spike protein of SARS-CoV-2 induces long-term immunization and prevents spike protein-mediated lung injury in mice.

While current anti-Spike protein (SP) vaccines have been pivotal in managing the pandemic, their limitations in delivery, storage, and the inability to provide mucosal immunization (preventing infections) highlight the ongoing necessity for research and innovation. To tackle these constraints, our research group developed a bacterial-based vaccine using a non-pathogenic E. coli Nissle 1917 (EcN) strain genetically modified to express the SARS-CoV-2 spike protein on its surface (EcN-pAIDA1-SP). We intranasally delivered the EcN-pAIDA1-SP in two doses and checked specific IgG/IgA production as well as the key immune mediators involved in the process. Moreover, following the initial and booster vaccine doses, we exposed both immunized and non-immunized mice to intranasal delivery of SARS-CoV-2 SP to assess the effectiveness of EcN-pAIDA1-SP in protecting lung tissue from the inflammation damage. We observed detectable levels of anti-SARS-CoV-2 spike IgG in serum samples and IgA in bronchoalveolar lavage fluid two weeks after the initial treatment, with peak concentrations in the respective samples on the 35th day. Moreover, immunoglobulins displayed a progressively enhanced avidity index, suggesting a selective binding to the spike protein. Finally, the pre-immunized group displayed a decrease in proinflammatory markers (TLR4, NLRP3, ILs) following SP challenge, compared to the non-immunized groups, along with better preservation of tissue morphology. Our probiotic-based technology provides an effective immunobiotic tool to protect individuals against disease and control infection spread.

Exploring Influenza A Virus-Induced Lung Injury and Immune Response Based on Humanized Lung-on-Chip.

BACKGROUND: Influenza is an important respiratory tract pathogen that causes substantial seasonal and pandemic morbidity and mortality. The aim of this study was to systematically analyze the transcriptome characteristics of peripheral blood mononuclear cells (PBMCs) after influenza A virus infection by constructing a human lung microarray model composed of PBMCs to simulate the influenza A virus infection process. METHODS: A human lung microarray model was constructed using alveolar epithelial cells, vascular endothelial cells, alveolar macrophages and PBMCs, for simulation of the process of influenza A virus infection. The transcriptome characteristics of PBMCs after influenza A virus infection were analyzed by a single-cell RNA sequencing system. RESULTS: The study could realistically mimic the structure and physiological functions of the alveoli in vitro using immunofluorescence staining and expression of the specific marker. After the influenza A virus infected the upper lung chip channels, the epithelial cells underwent a high inflammatory response and spread to endothelial cells. Under experimental conditions, the Influenza A virus infection did not compromise the integrity of epithelial cells, but caused damage to endothelial cells and barrier dysfunction. Single-cell RNA sequencing of PBMCs showed that B and cluster of differentiation 4 (CD4) T cells played important immunomodulatory roles in response to influenza A virus infection, including significantly activating type I interferon signaling pathway, regulating cytokine and chemokine signaling pathway. Especially genes involved in cellular communication were significantly highly expressed post-infection. CONCLUSIONS: All these results suggested that the interactions among immune cells played a crucial role in endothelial cell injury and immune cell recruitment after influenza virus infection. This lung-on-chip infection model combined with single-cell RNA sequencing provided a unique platform that can closely investigate the lung immune response to influenza A virus infection and new therapeutic strategies for influenza.

Fibroblast growth factor 10 protects against particulate matter-induced lung injury by inhibiting oxidative stress-mediated pyroptosis via the PI3K/Akt/Nrf2 signaling pathway.

Particulate matter (PM) is a major environmental contaminant that causes and worsens respiratory diseases. Fibroblast growth factor 10 (FGF10), a paracrine fibroblast growth factor that specifically stimulates repair and regeneration after injury, has been shown to protect against PM-induced lung injury. However, the underlying mechanisms are still unclear. In this study, the protective effects of FGF10 were investigated using a PM-induced lung injury mouse model in vivo and BEAS-2B cells in vitro. According to the findings, FGF10 treatment alleviated PM-induced oxidative damage and pyroptosis in vivo and in vitro. Mechanistically, FGF10 activated antioxidative Nrf2 signaling. Inhibition of PI3K signaling with LY294002 or Nrf2 signaling with ML385 revealed that FGF10-mediated lung protection was mediated by the PI3K/Akt/Nrf2 pathway. These results collectively indicate that FGF10 inhibits oxidative stress-mediated pyroptosis via the PI3K/Akt/Nrf2 pathway, suggesting a possible therapy for PM-induced lung injury.

Targeting chronic COVID-19 lung injury; Tofacitinib can be used against tissue-resident memory T cells.

Post-Covid pulmonary fibrosis is evident following severe COVID-19. There is an urgent need to identify the cellular and pathophysiological characteristics of chronic lung squeals of Covid-19 for the development of future preventive and/or therapeutic interventions. Tissue-resident memory T (TRM) cells can mediate local immune protection against infections and cancer. Less beneficially, lung TRM cells cause chronic airway inflammation and fibrosis by stimulating pathologic inflammation. The effects of Janus kinase (JAK), an inducer pathway of cytokine storm, inhibition on acute Covid-19 cases have been previously evaluated. Here, we propose that Tofacitinib by targeting the CD8+ TRM cells could be a potential candidate for the treatment of chronic lung diseases induced by acute SARS-CoV-2 infection.

Ultrastructural findings of lung injury due to Vaccine-induced Immune Thrombotic Thrombo- cytopenia (VITT) following COVID-19 vaccination: a scanning electron microscopic study.

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare new syndrome occurring after the ChAdOx1 nCoV-19 vaccine immunization. Patients with VITT are characterized by a variable clinical presentation, likewise also the outcome of these patients is very variable. Here we report the lung ultrastructural findings in the course of VITT of a 58-year-old male patient. Alveoli were mainly dilated, irregular in shape, and occupied by a reticular network of fibrin, while interalveolar septa appeared thickened. The proliferation of small capillaries gave rise to plexiform structures and pulmonary capillary hemangiomatosis-like features. Near the alveoli occupied by a dense fibrin network, the medium-sized arteries showed a modified wall and an intraluminal thrombus. This scenario looks quite similar to that found during COVID-19, where the lungs suffer from the attack of the antigen-antibodies complexes and the virus respectively. In both diseases, the final outcome is a severe inflammation, activation of the haemostatic system and fibrinolysis.

Neutrophil-Mediated Lung Injury Both via TLR2-Dependent Production of IL-1α and IL-12 p40, and TLR2-Independent CARDS Toxin after Mycoplasma pneumoniae Infection in Mice.

Mycoplasma pneumoniae (Mp) residing extracellularly in the respiratory tract is the primary cause of bacterial community-acquired pneumonia in humans. However, the detailed pathological mechanism of Mp infection, especially inflammation in the lung, remains unclear. This study examined the role of the neutrophils in the inflammation of Mp-induced pneumonia in mice and the mechanism of neutrophil infiltration into the lungs in the Mp-induced pneumonia. We observed massive infiltration of neutrophils in the bronchoalveolar lavage fluid (BALF) and lung injury after the Mp challenge. The neutrophils were shown to contribute to lung injury in Mp pneumonia but were not involved in eliminating Mp, suggesting that neutrophils are detrimental to the host in Mp pneumonia. Mp also induced the production of inflammatory cytokines and chemokines in the BALF in a toll-like receptor 2 (TLR2)-dependent manner. Particularly, both interleukin (IL)-1α and IL-12 p40 played a crucial role in neutrophil infiltration into the BALF in a coordinated manner. Both IL-1α and IL-12 p40 were released from the alveolar macrophages depending on the TLR2 and reactive oxygen species. In addition, the community-acquired respiratory distress syndrome (CARDS) toxin from Mp were found to induce neutrophil infiltration into BALF in a TLR2-independent and IL-1α-dependent manner. Collectively, the TLR2-dependent production of both IL-1α and IL-12 p40, and CARDS toxin have been elucidated to play an important role in neutrophil infiltration into the lungs subsequently leading to the lung injury upon Mp infection in mice. These data will aid in the development of therapeutics and vaccines for Mp pneumonia. IMPORTANCE Although Mp-induced pneumonia is usually a self-limiting disease, refractory life-threatening pneumonia is often induced. In addition, the development of alternative therapeutic strategies for Mp is expected because of the emergence of antibiotic-resistant Mp. However, the lack of knowledge regarding the pathogenesis of Mp-induced pneumonia, especially inflammation upon the Mp infection, makes it tedious to design novel therapeutics and vaccines. For example, although neutrophil infiltration is widely recognized as one of the characteristics of Mp-induced pneumonia, the precise role of neutrophils in the aggravation of Mp pneumonia remains unclear. This study showed that the infiltration of neutrophils in the lungs is detrimental to the host in Mp-induced pneumonia in mice. Furthermore, the TLR2-dependent IL-1α and IL-12 p40 production, and CARDS toxin play important roles in neutrophil infiltration into the lung, following lung injury. Our findings apply to the rational design of novel therapeutics and vaccines against Mp.

Increased Monocyte-Derived CD11b+ Macrophage Subpopulations Following Cigarette Smoke Exposure Are Associated With Impaired Bleomycin-Induced Tissue Remodelling.

Rationale: The accumulation of macrophages in the airways and the pulmonary interstitium is a hallmark of cigarette smoke-associated inflammation. Notably, pulmonary macrophages are not a homogenous population but consist of several subpopulations. To date, the manner in which cigarette smoke exposure affects the relative composition and functional capacity of macrophage subpopulations has not been elucidated. Methods: Using a whole-body cigarette smoke exposure system, we investigated the impact of cigarette smoke on macrophage subpopulations in C57BL/6 mice using flow cytometry-based approaches. Moreover, we used bromodeoxyuridine labelling plus Il1a-/- and Il1r1-/- mice to assess the relative contribution of local proliferation and monocyte recruitment to macrophage accumulation. To assess the functional consequences of altered macrophage subpopulations, we used a model of concurrent bleomycin-induced lung injury and cigarette smoke exposure to examine tissue remodelling processes. Main Results: Cigarette smoke exposure altered the composition of pulmonary macrophages increasing CD11b+ subpopulations including monocyte-derived alveolar macrophages (Mo-AM) as well as interstitial macrophages (IM)1, -2 and -3. The increase in CD11b+ subpopulations was observed at multiple cigarette smoke exposure timepoints. Bromodeoxyuridine labelling and studies in Il1a-/- mice demonstrated that increased Mo-AM and IM3 turnover in the lungs of cigarette smoke-exposed mice was IL-1α dependent. Compositional changes in macrophage subpopulations were associated with impaired induction of fibrogenesis including decreased α-smooth muscle actin positive cells following intratracheal bleomycin treatment. Mechanistically, in vivo and ex vivo assays demonstrated predominant macrophage M1 polarisation and reduced matrix metallopeptidase 9 activity in cigarette smoke-exposed mice. Conclusion: Cigarette smoke exposure modified the composition of pulmonary macrophage by expanding CD11b+ subpopulations. These compositional changes were associated with attenuated fibrogenesis, as well as predominant M1 polarisation and decreased fibrotic activity. Overall, these data suggest that cigarette smoke exposure altered the composition of pulmonary macrophage subpopulations contributing to impaired tissue remodelling.

Mesenchymal stem cell therapy for severe COVID-19.

The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has placed a global public burden on health authorities. Although the virological characteristics and pathogenesis of COVID-19 has been largely clarified, there is currently no specific therapeutic measure. In severe cases, acute SARS-CoV-2 infection leads to immune disorders and damage to both the adaptive and innate immune responses. Having roles in immune regulation and regeneration, mesenchymal stem cells (MSCs) serving as a therapeutic option may regulate the over-activated inflammatory response and promote recovery of lung damage. Since the outbreak of the COVID-19 pandemic, a series of MSC-therapy clinical trials has been conducted. The findings indicate that MSC treatment not only significantly reduces lung damage, but also improves patient recovery with safety and good immune tolerance. Herein, we summarize the recent progress in MSC therapy for COVID-19 and highlight the challenges in the field.

Enhanced eosinophil-mediated inflammation associated with antibody and complement-dependent pneumonic insults in critical COVID-19.

Despite the worldwide effect of the coronavirus disease 2019 (COVID-19) pandemic, the underlying mechanisms of fatal viral pneumonia remain elusive. Here, we show that critical COVID-19 is associated with enhanced eosinophil-mediated inflammation when compared to non-critical cases. In addition, we confirm increased T helper (Th)2-biased adaptive immune responses, accompanying overt complement activation, in the critical group. Moreover, enhanced antibody responses and complement activation are associated with disease pathogenesis as evidenced by formation of immune complexes and membrane attack complexes in airways and vasculature of lung biopsies from six fatal cases, as well as by enhanced hallmark gene set signatures of Fcγ receptor (FcγR) signaling and complement activation in myeloid cells of respiratory specimens from critical COVID-19 patients. These results suggest that SARS-CoV-2 infection may drive specific innate immune responses, including eosinophil-mediated inflammation, and subsequent pulmonary pathogenesis via enhanced Th2-biased immune responses, which might be crucial drivers of critical disease in COVID-19 patients.

Effects of fatty acid nitroalkanes on signal transduction pathways and airway macrophage activation.

Fatty acid nitroalkenes are reversibly-reactive electrophiles that are endogenously detectable at nM concentrations and display anti-inflammatory, pro-survival actions. These actions are elicited through the alteration of signal transduction proteins via a Michael addition on nucleophilic cysteine thiols. Nitrated fatty acids (NO2-FAs), like 9- or 10-nitro-octadec-9-enolic acid, will act on signal transduction proteins directly or on key regulatory proteins to cause an up-regulation or down-regulation of the protein's expression, yielding an anti-inflammatory response. These responses have been characterized in many organ systems, such as the cardiovascular system, with the pulmonary system less well defined. Macrophages are one of the most abundant immune cells in the lung and are essential in maintaining lung homeostasis. Despite this, macrophages can play a role in both acute and chronic lung injury due to up-regulation of anti-inflammatory signal transduction pathways and down-regulation of pro-inflammatory pathways. Through their propensity to alter signal transduction pathways, NO2-FAs may be able to reduce macrophage activation during pulmonary injury. This review will focus on the implications of NO2-FAs on macrophage activation in the lung and the signal transduction pathways that may be altered, leading to reduced pulmonary injury.

Extracellular vesicles of P. gingivalis-infected macrophages induce lung injury.

Periodontal diseases are common inflammatory diseases that are induced by infection with periodontal bacteria such as Porphyromonas gingivalis (Pg). The association between periodontal diseases and many types of systemic diseases has been demonstrated; the term "periodontal medicine" is used to describe how periodontal infection/inflammation may impact extraoral health. However, the molecular mechanisms by which the factors produced in the oral cavity reach multiple distant organs and impact general health have not been elucidated. Extracellular vesicles (EVs) are nano-sized spherical structures secreted by various types of cells into the tissue microenvironment, and influence pathophysiological conditions by delivering their cargo. However, a detailed understanding of the effect of EVs on periodontal medicine is lacking. In this study, we investigated whether EVs derived from Pg-infected macrophages reach distant organs in mice and influence the pathophysiological status. EVs were isolated from human macrophages, THP-1 cells, infected with Pg. We observed that EVs from Pg-infected THP-1 cells (Pg-inf EVs) contained abundant core histone proteins such as histone H3 and translocated to the lungs, liver, and kidneys of mice. Pg-inf EVs also induced pulmonary injury, including edema, vascular congestion, inflammation, and collagen deposition causing alveoli destruction. The Pg-inf EVs or the recombinant histone H3 activated the NF-κB pathway, leading to increase in the levels of pro-inflammatory cytokines in human lung epithelial A549 cells. Our results suggest a possible mechanism by which EVs produced in periodontal diseases contribute to the progression of periodontal medicine.

Long-term survivors of murine sepsis are predisposed to enhanced LPS-induced lung injury and proinflammatory immune reprogramming.

Millions of people who survive sepsis each year are rehospitalized and die due to late pulmonary complications. To prevent and treat these complications, biomarkers and molecular mediators must be identified. Persistent immune reprogramming in the form of immunoparalysis and impaired host defense is proposed to mediate late pulmonary complications after sepsis, particularly new pulmonary infections. However, immune reprogramming may also involve enhanced/primed responses to secondary stimuli, although their contribution to long-term sepsis complications remains understudied. We hypothesize that enhanced/primed immune responses in the lungs of sepsis survivors are associated with late pulmonary complications. To this end, we developed a murine sepsis model using cecal ligation and puncture (CLP) followed 3 wk later by administration of intranasal lipopolysaccharide to induce inflammatory lung injury. Mice surviving sepsis exhibit enhanced lung injury with increased alveolar permeability, neutrophil recruitment, and enhanced Ly6Chi monocyte Tnf expression. To determine the mediators of enhanced lung injury, we performed flow cytometry and RNA sequencing of lungs 3 wk after CLP, prior to lipopolysaccharide. Sepsis survivor mice showed expanded Ly6Chi monocytes populations and increased expression of many inflammatory genes. Of these, S100A8/A9 was also elevated in the circulation of human sepsis survivors for months after sepsis, validating our model and identifying S100A8/A9 as a potential biomarker and therapeutic target for long-term pulmonary complications after sepsis. These data provide new insight into the importance of enhanced/primed immune responses in survivors of sepsis and establish a foundation for additional investigation into the mechanisms mediating this response.

Viral Respiratory Pathogens and Lung Injury.

Several viruses target the human respiratory tract, causing different clinical manifestations spanning from mild upper airway involvement to life-threatening acute respiratory distress syndrome (ARDS). As dramatically evident in the ongoing SARS-CoV-2 pandemic, the clinical picture is not always easily predictable due to the combined effect of direct viral and indirect patient-specific immune-mediated damage. In this review, we discuss the main RNA (orthomyxoviruses, paramyxoviruses, and coronaviruses) and DNA (adenoviruses, herpesviruses, and bocaviruses) viruses with respiratory tropism and their mechanisms of direct and indirect cell damage. We analyze the thin line existing between a protective immune response, capable of limiting viral replication, and an unbalanced, dysregulated immune activation often leading to the most severe complication. Our comprehension of the molecular mechanisms involved is increasing and this should pave the way for the development and clinical use of new tailored immune-based antiviral strategies.

Methamphetamine facilitates pulmonary and splenic tissue injury and reduces T cell infiltration in C57BL/6 mice after antigenic challenge.

Methamphetamine (METH) is a strong addictive central nervous system stimulant. METH abuse can alter biological processes and immune functions necessary for host defense. The acquisition and transmission of HIV, hepatitis, and other communicable diseases are possible serious infectious consequences of METH use. METH also accumulates extensively in major organs. Despite METH being a major public health and safety problem globally, there are limited studies addressing the impact of this popular recreational psychostimulant on tissue adaptive immune responses after exposure to T cell dependent [ovalbumin (OVA)] and independent [lipopolysaccharide (LPS)] antigens. We hypothesized that METH administration causes pulmonary and splenic tissue alterations and reduces T cell responses to OVA and LPS in vivo, suggesting the increased susceptibility of users to infection. Using a murine model of METH administration, we showed that METH causes tissue injury, apoptosis, and alters helper and cytotoxic T cell recruitment in antigen challenged mice. METH also reduces the expression and distribution of CD3 and CD28 molecules on the surface of human Jurkat T cells. In addition, METH decreases the production of IL-2 in these T-like cells, suggesting a negative impact on T lymphocyte activation and proliferation. Our findings demonstrate the pleotropic effects of METH on cell-mediated immunity. These alterations have notable implications on tissue homeostasis and the capacity of the host to respond to infection.

Carvacrol and PPARγ agonist, pioglitazone, affects inhaled paraquat-induced lung injury in rats.

Exposed rats to normal saline and paraquat (PQ) aerosol as control and PQ group, rats exposed to PQ and treated with 20 and 80 mg/kg/day carvacrol, 5 and 10 mg/kg/day pioglitazone, low dose of pioglitazone + carvacrol and 0.03 mg/kg/day dexamethasone (Dexa) for 16 days after the end of PQ exposure were studied (n = 6 in each group). Lung pathological changes, tracheal responsiveness to methacholine and ovalbumin (OVA) as well as transforming growth factor beta (TGF-ß) and interleukin (IL)-6 level in the lung tissue homogenize as well as TGF-ß, IL-6, oxidant and antioxidant levels oxidant and antioxidants were increased in PQ group (p < 0.01 to p < 0.001). Lung pathological changes, tracheal responsiveness to methacholine and OVA as well as TGF-ß, IL-6 oxidant and antioxidant levels were improved in all treated groups except lung pathological changes in treated group with low dose of pioglitazone (p < 0.05 to p < 0.001). The effects of low dose of pioglitazone and carvacrol alone were significantly lower than in the combination group of low dose of pioglitazone + carvacrol (p < 0.05 to p < 0.001). Carvacrol treatment improved inhaled PQ-induced lug injury similar to the effects of dexamethasone. The synergic effect of carvacrol and pioglitazone suggests PPAR-γ receptor mediated effects of carvacrol on inhaled PQ-induced lung injury.

Activation of classical and alternative complement pathways in the pathogenesis of lung injury in COVID-19.

Lung inflammation and damage is prominent in people infected with SARS-Cov-2 and a major determinant of morbidity and mortality. We report the deposition of complement components in the lungs of people who succumbed to COVID-19 consistent with the activation of the classical and the alternative pathways. Our study provides strong rationale for the expansion of trials involving the use of complement inhibitors to treat patients with COVID-19.

Survival and Pulmonary Injury After Neonatal Sepsis: PD1/PDL1's Contributions to Mouse and Human Immunopathology.

Morbidity and mortality associated with neonatal sepsis remains a healthcare crisis. PD1-/- neonatal mice endured experimental sepsis, in the form of cecal slurry (CS), and showed improved rates of survival compared to wildtype (WT) counterparts. End-organ injury, particularly of the lung, contributes to the devastation set forth by neonatal sepsis. PDL1-/- neonatal mice, in contrast to PD1-/- neonatal mice did not have a significant improvement in survival after CS. Because of this, we focused subsequent studies on the impact of PD1 gene deficiency on lung injury. Here, we observed that at 24 h post-CS (but not at 4 or 12 h) there was a marked increase in pulmonary edema (PE), neutrophil influx, myeloperoxidase (MPO) levels, and cytokine expression sham (Sh) WT mice. Regarding pulmonary endothelial cell (EC) adhesion molecule expression, we observed that Zona occludens-1 (ZO-1) within the cell shifted from a membranous location to a peri-nuclear location after CS in WT murine cultured ECs at 24hrs, but remained membranous among PD1-/- lungs. To expand the scope of this inquiry, we investigated human neonatal lung tissue. We observed that the lungs of human newborns exposed to intrauterine infection had significantly higher numbers of PD1+ cells compared to specimens who died from non-infectious causes. Together, these data suggest that PD1/PDL1, a pathway typically thought to govern adaptive immune processes in adult animals, can modulate the largely innate neonatal pulmonary immune response to experimental septic insult. The potential future significance of this area of study includes that PD1/PDL1 checkpoint proteins may be viable therapeutic targets in the septic neonate.

Trauma-induced lung injury is associated with infiltration of activated TLR expressing myeloid cells.

INTRODUCTION: Traumatic injury with hemorrhage (TH) induces an inflammatory response in the lung resulting in lung injury involving activation of immune cells including myeloid cells (i.e., monocytes, granulocytes and macrophages), in part through TLRs. TLRs, via the recognition of damage associated molecular patterns (DAMPs), are a key link between tissue injury and inflammation. Nonetheless, the role of TLRs in myeloid cell activation and TH-induced lung injury remains ill defined. METHODS: C57BL/6 male mice were subjected to TH or sham treatment (n = 4-6 /group). Lung tissues were collected two hrs. after injury. Single cells were isolated from the lungs by enzymatic digestion and myeloid cell TLR expression and activation (i.e., cytokine production) were assessed using flow cytometry techniques. RESULTS: The injury was associated with a profound change in the lung myeloid cell population. TH markedly increased lung CD11b+ monocyte numbers and Gr1+ granulocyte numbers as compared to sham mice. The number of cells expressing TLR2, TLR4, and TLR9 were increased 4-7 fold in the TH mice. Activation for elevated cytokine (TNFα, IL-10) production was observed in the lung monocyte population of the TH mice. CONCLUSIONS: Trauma-induced lung injury is associated with infiltration of the lungs with TLR expressing myeloid cells that are activated for elevated cytokine responses. This elevation in TLR expression may contribute to DAMP-mediated pulmonary complications of an inflammatory nature and warrants further investigation.

The pulmonary metatranscriptome prior to pediatric HCT identifies post-HCT lung injury.

Lung injury after pediatric allogeneic hematopoietic cell transplantation (HCT) is a common and disastrous complication that threatens long-term survival. To develop strategies to prevent lung injury, novel tools are needed to comprehensively assess lung health in HCT candidates. Therefore, this study analyzed biospecimens from 181 pediatric HCT candidates who underwent routine pre-HCT bronchoalveolar lavage (BAL) at the University Medical Center Utrecht between 2005 and 2016. BAL fluid underwent metatranscriptomic sequencing of microbial and human RNA, and unsupervised clustering and generalized linear models were used to associate microbiome gene expression data with the development of post-HCT lung injury. Microbe-gene correlations were validated using a geographically distinct cohort of 18 pediatric HCT candidates. The cumulative incidence of post-HCT lung injury varied significantly according to 4 pre-HCT pulmonary metatranscriptome clusters, with the highest incidence observed in children with pre-HCT viral enrichment and innate immune activation, as well as in children with profound microbial depletion and concomitant natural killer/T-cell activation (P < .001). In contrast, children with pre-HCT pulmonary metatranscriptomes containing diverse oropharyngeal taxa and lacking inflammation rarely developed post-HCT lung injury. In addition, activation of epithelial-epidermal differentiation, mucus production, and cellular adhesion were associated with fatal post-HCT lung injury. In a separate validation cohort, associations among pulmonary respiratory viral load, oropharyngeal taxa, and pulmonary gene expression were recapitulated; the association with post-HCT lung injury needs to be validated in an independent cohort. This analysis suggests that assessment of the pre-HCT BAL fluid may identify high-risk pediatric HCT candidates who may benefit from pathobiology-targeted interventions.

The Immunopathological and Histological Landscape of COVID-19-Mediated Lung Injury.

A complete understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) physiopathology and related histopathologic lesions is necessary to improve treatment and outcome of coronavirus disease 2019 (COVID-19) patients. Many studies have focused on autopsy findings in COVID-19-related deaths to try and define any possible specific pattern. Histopathologic alterations are principally found within lungs and blood vessels, and these abnormalities also seem to have the highest clinical impact. Nevertheless, many of the morphological data collected so far are non-specific, fickle, and possibly associated with other co-existing factors. The aim of this minireview is to describe the main histopathological features related to COVID-19 and the mechanism known as "cytokine storm".