Early humoral defence: Contributing to confining COVID-19 to conducting airways?

Early airway responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection are of interest since they could decide whether coronavirus disease-19 (COVID-19) will proceed to life-threatening pulmonary disease stages. Here I discuss endothelial-epithelial co-operative in vivo responses producing first-line, humoral innate defence opportunities in human airways. The pseudostratified epithelium of human nasal and tracheobronchial airways are prime sites of exposure and infection by SARS-CoV-2. Just beneath the epithelium runs a profuse systemic microcirculation. Its post-capillary venules respond conspicuously to mucosal challenges with autacoids, allergens and microbes, and to mere loss of epithelium. By active venular endothelial gap formation, followed by transient yielding of epithelial junctions, non-sieved plasma macromolecules move from the microcirculation to the mucosal surface. Hence, plasma-derived protein cascade systems and antimicrobial peptides would have opportunity to operate jointly on an unperturbed mucosal lining. Similarly, a plasma-derived, dynamic gel protects sites of epithelial sloughing-regeneration. Precision for this indiscriminate humoral molecular response lies in restricted location and well-regulated duration of plasma exudation. Importantly, the endothelial responsiveness of the airway microcirculation differs distinctly from the relatively non-responsive, low-pressure pulmonary microcirculation that non-specifically, almost irreversibly, leaks plasma in life-threatening COVID-19. Observations in humans of infections with rhinovirus, coronavirus 229E, and influenza A and B support a general but individually variable early occurrence of plasma exudation in human infected nasal and tracheobronchial airways. Investigations are warranted to elucidate roles of host- and drug-induced airway plasma exudation in restriction of viral infection and, specifically, whether it contributes to variable disease responses following exposure to SARS-CoV-2.

Airways exudation of plasma macromolecules: Innate defense, epithelial regeneration, and asthma.

This review discusses in vivo airway aspects of plasma exudation in relation to current views on epithelial permeability and epithelial regeneration in health and disease. Microvascular-epithelial exudation of bulk plasma proteins characteristically occurs in asthmatic patients, being especially pronounced in those with severe and exacerbating asthma. Healthy human and guinea pig airways challenged by noninjurious histamine-leukotriene-type autacoids also respond through prompt mucosal exudation of nonsieved plasma macromolecules. Contrary to current beliefs, epithelial permeability in the opposite direction (ie, absorption of inhaled molecules) has not been increased in patients with asthma and allergic rhinitis or in acutely exuding healthy airways. A slightly increased subepithelial hydrostatic pressure produces such unidirectional outward perviousness to macromolecules. Lack of increased absorption permeability in asthmatic patients can further be reconciled with occurrence of epithelial shedding, leaving small patches of denuded basement membrane. Counteracting escalating barrier breaks, plasma exudation promptly covers the denuded patches. Here it creates and sustains a biologically active barrier involving a neutrophil-rich, fibrin-fibronectin net. Furthermore, in the plasma-derived milieu, all epithelial cell types bordering the denuded patch dedifferentiate and migrate from all sides to cover the denuded basement membrane. However, this speedy epithelial regeneration can come at a cost. Guinea pig in vivo studies demonstrate that patches of epithelial denudation regeneration are exudation hot spots evoking asthma-like features, including recruitment/activation of granulocytes, proliferation of fibrocytes/smooth muscle cells, and basement membrane thickening. In conclusion, nonsieved plasma macromolecules can operate on the intact airway mucosa as potent components of first-line innate immunity responses. Exuded plasma also takes center stage in epithelial regeneration. When exaggerated, epithelial regeneration can contribute to the inception and development of asthma.

In vivo observations provide insight into roles of eosinophils and epithelial cells in asthma.

Observations in vivo in patients, supported by guinea-pig in vivo data, take centre stage in this perspective. Its objective is to highlight dichotomies between asthma features observed in vivo and accepted views involving cell/molecular biology research paradigms. For example, increased bronchial epithelial permeability is now considered a major paradigm and trait of asthma, yet, absorption of inhaled tracers has not been increased in vivo in asthma. Such maintained barrier function in exudative asthma reflects in vivo asymmetry of the epithelial lining as barrier between outside and inside world of molecules and cells. In desquamatory asthma, maintained epithelial tightness may be explained by in vivo demonstrations of exceedingly patchy epithelial loss, prompt creation of plasma-derived provisional barriers, and high-speed epithelial regeneration. Acknowledged protein/peptide secretion by epithelial cells in vitro is contrasted here with a dominant, unidirectional movement in vivo of plasma-derived proteins/peptides (including antimicrobial peptides) to the surface of an intact epithelial lining. Furthermore, longstanding claims that epithelium-produced adenosine is a mediator of asthma are eroded by observations in vivo in asthmatics. Notions concerning activation/fate of mucosal tissue eosinophils illustrate additional distinctions between accepted views and in vivo patient observations. Finally, in vitro-based paradigms preaching defect epithelial regeneration and increased permeability in pathogenesis of asthma are contrasted with experimental in vivo observations of exaggerated epithelial regeneration, which is multipathogenic in its own right. In conclusion, unexpected and challenging in vivo observations in recent decades underpin novel insights into mucosal mechanisms in asthma.

Does a Novice Technician Produce Results Similar to That of an Experienced DXA Technician When Assessing Body Composition and Bone Mineral Density?

Dual-energy X-ray absorptiometry is a commonly used clinical assessment tool for body composition and bone mineral density, which is gaining popularity in athletic cohorts. Results from body composition scans are useful for athletic populations to track training and nutritional interventions, while bone mineral density scans are valuable for athletes at risk of developing stress fractures due to low bone mineral density. However, no research has ascertained if a novice technician (accredited but not experienced) could produce similar results to an experienced technician. Two groups of recreational athletes were scanned, one by an experienced technician, one by a novice technician. All participants were scanned twice with repositioning between scans. The experienced technician's reliability (intraclass correlation coefficient = .989-.998; percentage change in mean = -0.01 to 0.10), precision (typical error as coefficient of variation percentage = 0.01-0.47; SEM% = 0.61-1.39), and sensitivity to change (smallest real difference percentage = 1.70-3.85) were similar; however, superior to those of the novice technician. The novice technician results were reliability (intraclass correlation coefficient = .985-.997; percentage change in mean = -0.03 to 0.23), precision (typical error as coefficient of variation percentage = 0.03-0.75; SEM% = 1.06-2.12), and sensitivity to change (smallest real difference percentage = 2.73-5.86). Extensive experience, while valuable, is not a necessary requirement to produce quality results when undertaking whole-body dual-energy X-ray absorptiometry scanning.

Reliability and Precision of the Nana Protocol to Assess Body Composition Using Dual Energy X-Ray Absorptiometry.

The Nana positioning protocol is widely used to position participants to minimize technical error when undertaking body composition scanning and analysis with a Dual energy X-Ray absorptiometry (DXA) machine. Once biological and technical errors are accounted for, the only variation in test-retest results is from statistical fluctuation or machine error. Therefore, the aim of this study is to assess the test-retest reliability of the Nana positioning protocol and establish the smallest real difference percentage (SRD%). A gender-balanced group of 30 participants (15 males, 15 females) underwent two scans in succession using the Nana positioning protocol, with repositioning between scans. Percentage change in mean with typical error, Intraclass Correlation Coefficients (ICC), and standard error measurement percentage (SEM%) were used to identify the test-retest reliability and error rate of these protocols. Additionally, SRD% was calculated to assess the point at which clinically important changes occurred in a participant. The reliabilities of the whole body and regional scans were excellent. Percentage change in mean ranged between 0.00% and 0.23%. High reproducibility of the Nana positioning protocol was evident through an ICC ranging between 0.966-1.000. Additionally, typical error, SEM%, and SRD% were all low. Interestingly, fat mass was associated with the largest fluctuations observed to be associated with any of the parameters assessed. When all sources of biological and technical errors have been accounted for, the Nana positioning protocol has excellent test-retest reliability and produces low SEM% and SRD%.

Well-controlled mucosal exudation of plasma proteins in airways with intact and regenerating epithelium.

Superficial, systemic microcirculations, distinct from the pulmonary circulation, supply the mucosae of human nasal and conducting airways. Non-injurious, inflammatory challenges of the airway mucosa cause extravasation without overt mucosal oedema. Instead, likely reflecting minimal increases in basolateral hydrostatic pressure, circulating proteins/peptides of all sizes are transmitted paracellularly across the juxtaposed epithelial barrier. Thus, small volumes of extravasated, unfiltered bulk plasma appear on the mucosal surface at nasal and bronchial sites of challenge. Importantly, the plasma-exuding mucosa maintains barrier integrity against penetrability of inhaled molecules. Thus, one-way epithelial penetrability, strict localization, and well-controlled magnitude and duration are basic characteristics of the plasma exudation response in human intact airways. In vivo experiments in human-like airways demonstrate that local plasma exudation is also induced by non-sanguineous removal of epithelium over an intact basement membrane. This humoral response results in a protective, repair-promoting barrier kept together by a fibrin-fibronectin net. Plasma exudation stops once the provisional barrier is substituted by a new cellular cover consisting of speedily migrating repair cells, which may emanate from all types of epithelial cells bordering the denuded patch. Exuded plasma on the surface of human airways reflects physiological microvascular-epithelial cooperation in first line mucosal defense at sites of intact and regenerating epithelium.

dsRNA-induced expression of thymic stromal lymphopoietin (TSLP) in asthmatic epithelial cells is inhibited by a small airway relaxant.

RATIONALE: Thymic Stromal Lymphopoietin (TSLP) is considered a hub cytokine that activates dendritic cells and T-cells producing asthma-like Th2-inflammation. Viral stimuli, a major cause of asthma exacerbations, have been shown to induce overexpression of TSLP in asthmatic epithelium. Capsazepine has multiple effects and is of interest because it relaxes human small airways. Here we have explored effects of capsazepine on viral surrogate (dsRNA)-induced TSLP and other cytokines (TNF-alpha, IL-8) in human bronchial epithelial cells (HBEC) from healthy and asthmatic donors. METHODS: HBEC obtained from healthy and asthmatic subjects were grown and stimulated with dsRNA. Cells pre-treated with capsazepine (3-30 µM), dexamethasone (0.1-10 µM) or an IkappaB-kinase inhibitor (PS1145, 30 µM) were also exposed to dsRNA (10 µg/ml). Cells and supernatants were harvested for analyses of gene expression (RT-qPCR) and protein production (ELISA,Western blot). RESULTS: dsRNA-induced TSLP, TNF-alpha, and IL-8 in asthmatic and non-asthmatic HBEC. Dexamethasone attenuated gene expression and protein release whereas capsazepine dose-dependently, and similar to a non-relaxant NFkB inhibitor (PS1145), completely inhibited dsRNA-induced TSLP and TNF-alpha in both healthy and asthmatic HBEC. Capsazepine reduced dsRNA-induced IL-8 and it prevented dsRNA-induced loss of the NF-κB repressor protein IkBα. CONCLUSION: Additional to its human small airway relaxant effects we now demonstrate that capsazepine has potent anti-inflammatory effects on viral stimulus-induced cytokines in HBEC from healthy as well as asthmatic donors. Based on these data we suggest that exploration of structure-activity amongst the multifaceted capsazepinoids is warranted in search for compounds of therapeutic value in viral-induced, steroid-resistant asthma.